67 articles on Friday, October 18


arXiv:1910.07523v1 [pdf, other]
A Hubble PanCET Study of HAT-P-11b: A Cloudy Neptune with a Low Atmospheric Metallicity
Comments: Accepted for publication in AJ. 33 pages, 23 figures

We present the first comprehensive look at the $0.35-5$ $\mu$m transmission spectrum of the warm ($\sim 800$ K) Neptune HAT-P-11b derived from thirteen individual transits observed using the Hubble and Spitzer Space Telescopes. Along with the previously published molecular absorption feature in the $1.1-1.7$ $\mu$m bandpass, we detect a distinct absorption feature at 1.15 $\mu$m and a weak feature at 0.95 $\mu$m, indicating the presence of water and/or methane with a combined significance of 4.4 $\sigma$. We find that this planet's nearly flat optical transmission spectrum and attenuated near-infrared molecular absorption features are best-matched by models incorporating a high-altitude cloud layer. Atmospheric retrievals using the combined $0.35-1.7$ $\mu$m HST transmission spectrum yield strong constraints on atmospheric cloud-top pressure and metallicity, but we are unable to match the relatively shallow Spitzer transit depths without under-predicting the strength of the near-infrared molecular absorption bands. HAT-P-11b's HST transmission spectrum is well-matched by predictions from our microphysical cloud models. Both forward models and retrievals indicate that HAT-P-11b most likely has a relatively low atmospheric metallicity ($<4.6 \; Z_{\odot}$ and $<86 \; Z_{\odot}$ at the $2 \sigma$ and $3 \sigma$ levels respectively), in contrast to the expected trend based on the solar system planets. Our work also demonstrates that the wide wavelength coverage provided by the addition of the HST STIS data is critical for making these inferences.


arXiv:1910.07524v1 [pdf, other]
An ALMA survey of the SCUBA-2 CLS UDS field: Physical properties of 707 Sub-millimetre Galaxies
Comments: No comment found

We analyse the physical properties of a large, homogeneously selected sample of ALMA-located sub-mm galaxies (SMGs) detected in the SCUBA-2 CLS 850-$\mu$m map of the UKIDSS/UDS field. This survey, AS2UDS, identified 707 SMGs across the ~1 sq.deg. field, including ~17 per cent which are undetected in the optical/near-infrared to $K$>~25.7 mag. We interpret the UV-to-radio data using a physically motivated model, MAGPHYS and determine a median photometric redshift of z=2.61+-0.08, with a 68th percentile range of z=1.8-3.4 and just ~6 per cent at z>4. The redshift distribution is well fit by a model combining evolution of the gas fraction in halos with the growth of halo mass past a threshold of ~4x10$^{12}$M$_\odot$, thus SMGs may represent the highly efficient collapse of gas-rich massive halos. Our survey provides a sample of the most massive, dusty galaxies at z>~1, with median dust and stellar masses of $M_d$=(6.8+-0.3)x10$^{8}$M$_\odot$ (thus, gas masses of ~10$^{11}$M$_\odot$) and $M_\ast=$(1.26+-0.05)x10$^{11}$M$_\odot$. These galaxies have gas fractions of $f_{gas}=$0.41+-0.02 with depletion timescales of ~150Myr. The gas mass function evolution at high masses is consistent with constraints at lower masses from blind CO-surveys, with an increase to z~2-3 and then a decline at higher redshifts. The space density and masses of SMGs suggests that almost all galaxies with $M_\ast$>~2x10$^{11}$M$_\odot$ have passed through an SMG-like phase. We find no evolution in dust temperature at a constant far-infrared luminosity across z~1.5-4. We show that SMGs appear to behave as simple homologous systems in the far-infrared, having properties consistent with a centrally illuminated starburst. Our study provides strong support for an evolutionary link between the active, gas-rich SMG population at z>1 and the formation of massive, bulge-dominated galaxies across the history of the Universe.


arXiv:1910.07526v1 [pdf, other]
Cross-correlation of the thermal Sunyaev-Zel'dovich effect and weak gravitational lensing: Planck and Subaru Hyper Suprime-Cam first-year data
Comments: 25 pages, 19 figures, submitted to MNRAS

Cross-correlation analysis of the thermal Sunyaev-Zel'dovich (tSZ) effect and weak gravitational lensing (WL) provides a powerful probe of cosmology and astrophysics of the intra-cluster medium. We present the measurement of the cross-correlation of tSZ and WL from Planck and Subaru Hyper-Suprime Cam. The combination enables us to study cluster astrophysics at high redshift. We use the tSZ-WL cross-correlation and the tSZ auto-power spectrum measurements to place a tight constraint on the hydrostatic mass bias, which is a measure of the degree of non-thermal pressure support in galaxy clusters. With the prior on cosmological parameters derived from the analysis of the cosmic microwave background anisotropies by Planck and taking into account foreground contributions both in the tSZ auto-power spectrum and the tSZ-WL cross-correlation, the hydrostatic mass bias is estimated to be $26.9^{+8.9}_{-4.4} \%$ ($68\%$ C.L.), which is consistent with recent measurements by mass calibration techniques.


arXiv:1910.07527v1 [pdf, other]
Transit Signatures of Inhomogeneous Clouds on Hot Jupiters: Insights From Microphysical Cloud Modeling
Comments: 21 pages, 17 figures, submitted to ApJ, revised following comments from referee

We determine the observability in transmission of inhomogeneous cloud cover on the limbs of hot Jupiters through post processing a general circulation model to include cloud distributions computed using a cloud microphysics model. We find that both the east and west limb often form clouds, but that the different properties of these clouds enhances the limb to limb differences compared to the clear case. Using JWST it should be possible to detect the presence of cloud inhomogeneities by comparing the shape of the transit lightcurve at multiple wavelengths because inhomogeneous clouds impart a characteristic, wavelength dependent signature. This method is statistically robust even with limited wavelength coverage, uncertainty on limb darkening coefficients, and imprecise transit times. We predict that the short wavelength slope varies strongly with temperature. The hot limb of the hottest planets form higher altitude clouds composed of smaller particles leading to a strong rayleigh slope. The near infrared spectral features of clouds are almost always detectable, even when no spectral slope is visible in the optical. In some of our models a spectral window between 5 and 9 microns can be used to probe through the clouds and detect chemical spectral features. Our cloud particle size distributions are not log-normal and differ from species to species. Using the area or mass weighted particle size significantly alters the relative strength of the cloud spectral features compared to using the predicted size distribution. Finally, the cloud content of a given planet is sensitive to a species' desorption energy and contact angle, two parameters that could be constrained experimentally in the future.


arXiv:1910.07528v1 [pdf, other]
Deepening the understanding of cosmic-ray diffusion
Comments: 18 pages, 6 figures

For the first time, we characterize the rigidity regimes of the diffusion coefficient $\kappa$ for arbitrary rigidities and guide fields, which we derive as a function of physical and numerical parameters. We show that at turbulence levels above 5\% of the total magnetic field, the approximation of an energy dependence $\kappa\propto E^{1/3}$ as predicted for a Kolmogorov spectrum within Quasi-Linear Theory does not hold. Consequently, a proper description of cosmic-ray propagation can only be achieved by using a turbulence-level dependent diffusion coefficient and can contribute to solving the Galactic cosmic-ray gradient problem.


arXiv:1910.07529v1 [pdf, other]
A Tip of the Red Giant Branch Distance to the Dark Matter Deficient Galaxy NGC 1052-DF4 from Deep Hubble Space Telescope Data
Comments: Submitted to ApJL. Figure 1 shows the color image of the galaxy. The main result is shown in Figure 4

Previous studies have shown that the large, diffuse galaxies NGC1052-DF2 and NGC1052-DF4 both have populations of unusually luminous globular clusters as well as a very low dark matter content. Here we present newly-obtained deep Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging of one of these galaxies, NGC1052-DF4. We use these data to measure an accurate distance of the galaxy from the location of the tip of the red giant branch (TRGB). We find a rapid increase in the number of detected stars fainter than $I_{814}\approx 27.3$, which we identify as the onset of the red giant branch. Using a forward modeling approach that takes the empirically-determined photometric uncertainties into account, we find a TRGB magnitude of $m_{I,\rm TRGB}=27.31 \pm 0.09$. The inferred distance, including the uncertainty in the absolute calibration, is $D_{\rm TRGB}=18.8^{+0.9}_{-1.1}$ Mpc. A standard edge-detection technique gives a very similar result. The TRGB distance of NGC1052-DF4 is consistent with the previously-determined surface brightness fluctuation distance of $D_{\rm SBF}=18.7\pm 1.7$ Mpc to NGC1052-DF2 and confirms that both galaxies are members of the NGC1052 group at $ \approx 19 \ \mathrm{Mpc}$. We conclude that the unusual properties of these galaxies cannot be explained by distance errors. The distance uncertainty can be further reduced with deeper data taken over multiple epochs, which will be obtained for NGC1052-DF2 in a Cycle 27 program.


arXiv:1910.07532v1 [pdf, other]
Normal type Ia supernovae from disruptions of hybrid He-CO white-dwarfs by CO white-dwarfs
Comments: Comments are welcomed

Type Ia supernovae (SNe) are thought to originate from the thermonuclear explosions of carbon-oxygen (CO) white dwarfs (WDs). The proposed progenitors of standard type Ia SNe have been studied for decades and can be, generally, divided into explosions of CO WDs accreting material from stellar non-degenerate companions (single-degenerate; SD models), and those arising from the explosive interaction of two CO WDs (double-degenerate; DD models). However, current models for the progenitors of such SNe fail to reproduce the diverse properties of the observed explosions, nor do they explain the inferred rates and the characteristics of the observed populations of type Ia SNe and their expected progenitors. Here we show that the little-studied mergers of CO-WDs with hybrid Helium-CO (He-CO) WDs can provide for a significant fraction of the normal type Ia SNe. Here we use detailed thermonuclear-hydrodynamical and radiative-transfer models to show that a wide range of mergers of CO WDs with hybrid He-CO WDs can give rise to normal type Ia SNe. We find that such He-enriched mergers give rise to explosions for which the synthetic light-curves and spectra resemble those of observed type Ia SNe, and in particular, they can produce a wide range of peak-luminosities, MB(MR)~ 18.4 to 19.2 (~ 18.5 to 19:45), consistent with those observed for normal type Ia SNe. Moreover, our population synthesis models show that, together with the contribution from mergers of massive double CO-WDs (producing the more luminous SNe), they can potentially reproduce the full range of type Ia SNe, their rate and delay-time distribution.


arXiv:1910.07536v1 [pdf, other]
The dark matter component of the Gaia radially anisotropic substructure
Comments: 29 pages, 14 figures, 6 tables

We study the properties of the dark matter component of the radially anisotropic stellar population recently identified in the Gaia data, using magneto-hydrodynamical simulations of Milky Way-like halos from the Auriga project. We identify 10 simulated galaxies that approximately match the rotation curve and stellar mass of the Milky Way. Four of these have an anisotropic stellar population reminiscent of the Gaia structure. We find an anti-correlation between the dark matter mass fraction of this population in the Solar neighbourhood and its orbital anisotropy. We estimate the local dark matter density and velocity distribution for halos with and without the anisotropic stellar population, and use them to simulate the signals expected in future xenon and germanium direct detection experiments. We find that a generalized Maxwellian distribution fits the dark matter halo integrals of the Milky Way-like halos containing the radially anisotropic stellar population. For dark matter particle masses below approximately 10 GeV, direct detection exclusion limits for the simulated halos with the anisotropic stellar population show a mild shift towards smaller masses compared to the commonly adopted Standard Halo Model.


arXiv:1910.07537v1 [pdf, other]
Analytical calculation of the numerical results of Khatami and Kasen for transient peak time and luminosity
Comments: 3 pages, 1 figure

The diffusion approximation is often used to study supernovae light-curves around peak light, where it is applicable. By analytic arguments and numerical studies of toy models, Khatami & Kasen (2019) recently argued for a new approximate relation between peak bolometric Luminosity, $L_p$, and the time of peak since explosion, $t_p$, for transients involving homologous expansion: $L_p=2/(\beta t_p)^2\int_0 ^{\beta t_{p}} t'Q(t')dt'$, where $Q(t)$ is the heating rate of the ejecta, and $\beta$ is an order unity parameter that is calibrated from numerical calculations. Khatami & Kasen (2019) demonstrated its validity using Monte-Carlo radiation transfer simulations of ejecta with homogenous density and (for most cases considered) constant opacity. Interestingly, constant values of $\beta$ accurately reproduce the numerical calculations for different heating distributions and over a wide range of energy release times. Here we show that the diffusion and the adiabatic loss of energy in homologous expansion is equivalent to a static diffusion equation and provide an analytic solution for the case of uniform density and opacity (extending the results of Pinto & Eastman 2000). Our accurate analytical solutions reproduce and extend the results of Khatami & Kasen (2019) for this case, allowing clarification for the universality of their peak time-luminosity relation as well as new limitations to its use.


arXiv:1910.07538v1 [pdf, other]
Dynamical Relics of the Ancient Galactic Halo
Comments: ApJ, submitted

We search for dynamical substructures in the LAMOST DR3 very metal-poor (VMP) star catalog. After cross-matching with Gaia DR2, there are 3300 VMP stars with available high-quality astrometric information that have halo-like kinematics. We apply a method based on self-organizing maps to find groups clustered in the 4D space of orbital energy and angular momentum. We identify 57 dynamically tagged groups, which we label DTG-1 to DTG-57. Most of them belong to existing substructures in the nearby halo, such as the $Gaia$ Sausage or Sequoia. The stream identified by Helmi et al. is recovered, but the two disjoint portions of the substructure have distinct dynamical properties. The very retrograde substructure Rg5 found previously by Myeong et al. is also retrieved. We report 6 new DTGs with highly retrograde orbits, 2 with very prograde orbits, and 12 with polar orbits. By mapping other datasets (APOGEE halo stars, and catalogs of r-process-enhanced and CEMP stars) onto the trained neuron map, we can associate stars with detailed chemical abundances to the DTGs, and look for associations with chemically peculiar stars. The highly eccentric $Gaia$ Sausage groups contain representatives both of debris from the satellite itself (which is $\alpha$-poor) and the Splashed Disk, sent up into eccentric halo orbits from the encounter (and is $\alpha$-rich). The new prograde substructures also appear to be associated with the Splashed Disk. The DTGs belonging to the $Gaia$ Sausage host two relatively metal-rich $r$-II stars and six CEMP stars in different sub-classes, consistent with the idea that the $Gaia$ Sausage progenitor is a massive dwarf galaxy. Rg5 is dynamically associated with two highly $r$-process-enhanced stars with [Fe/H] $\sim -$3. This finding indicates that its progenitor might be an ultra-faint dwarf galaxy that has experienced $r$-process enrichment from neutron star mergers.


arXiv:1910.07541v1 [pdf, other]
Testing Galaxy Formation Simulations with Damped Lyman-$α$ Abundance and Metallicity Evolution
Comments: submitted to MNRAS, comments are welcome

We examine the properties of damped Lyman-${\alpha}$ absorbers (DLAs) emerging from a single set of cosmological initial conditions in two state-of-the-art cosmological hydrodynamic simulations: Simba and Technicolor Dawn. The former includes star formation and black hole feedback treatments that yield a good match with low-redshift galaxy properties, while the latter uses multi-frequency radiative transfer to model an inhomogeneous ultraviolet background (UVB) self-consistently and is calibrated to match the Thomson scattering optical depth, UVB amplitude, and Lyman-${\alpha}$ forest mean transmission at z $>$ 5. Both simulations are in reasonable agreement with the measured stellar mass and star formation rate functions at z $\geq$ 3, and both reproduce the observed neutral hydrogen cosmological mass density, $\Omega_{\rm HI}(z)$. However, the DLA abundance and metallicity distribution are sensitive to the galactic outflows feedback and the UVB amplitude. Adopting a strong UVB and/or slow outflows under-produces the observed DLA abundance, but yields broad agreement with the observed DLA metallicity distribution. By contrast, faster outflows eject metals to larger distances, yielding more metal-rich DLAs whose observational selection may be more sensitive to dust bias. The DLA metallicity distribution in models adopting an H2-regulated star formation recipe includes a tail extending to [M/H] $\ll$ -3, lower than any DLA observed to date, owing to curtailed star formation in low-metallicity galaxies. Our results show that DLA observations play an important role in constraining key physical ingredients in galaxy formation models, complementing traditional ensemble statistics such as the stellar mass and star formation rate functions.


arXiv:1910.07544v1 [pdf, other]
Massive and old quiescent galaxies at high redshift
Comments: Astronomy & Astrophysics, accepted; 21 pages, 13 figures

Massive quiescent galaxies at high redshift can shed light on the processes of galaxy mass assembly and quenching of the star formation at early epochs. We present observer-frame color-color diagrams designed to identify candidate quiescent galaxies from z=2.5 up to the highest redshifts, that can be then be selected for spectroscopic follow-up observations. The application to the COSMOS2015 catalog shows that, after refining the selection with SED fitting, the number of massive old quiescent galaxies exceeds the forecast of state-of-the-art semi-analytic models, pointing out the need of an improvement of the implemented quenching mechanisms at high redshifts.


arXiv:1910.07547v1 [pdf, other]
The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
Comments: 14 pages, 11 figures. Accepted for publication in MNRAS

We use the Pristine survey CaHK narrow-band photometry, combined with the SDSS ugr photometry, to provide a cleaner sample of blue horizontal branch stars in the Galactic halo out to large distances. We demonstrate a completeness of 91% and a purity of 93% with respect to available spectroscopic classifications. We subsequently use our new clean sample of these standard candles to investigate the substructure in the Galactic halo over the Pristine footprint. Among other features, this allows for a careful tracing of multiple parts of the Sagittarius stream, providing a measurement independent from other tracers used and reaching larger distances. Moreover, we demonstrate with this clean and complete sample that the halo follows a density profile with a negative power-law slope of 3.5 - 4.0. As the relatively shallow SDSS u-band is the limiting factor in this technique, we foresee large potential for combining Pristine survey photometry with the much deeper u-band photometry from the Canada-France-Imaging Survey.


arXiv:1910.07550v1 [pdf, other]
Impact of X-rays on CO emission from high-z galaxies
Comments: accepted for publication in MNRAS

We study the impact of active galactic nuclei (AGN) on the CO Spectral Line Energy Distribution (SLED) of high-$z$ galaxies. In particular, we want to assess if the CO SLED can be used as a probe of AGN activity. To this purpose, we develop a semi-analytical model that takes into account the radiative transfer and the clumpy structure of giant molecular clouds where the CO lines are excited, their distribution in the galaxy disk, and the torus obscuration of the AGN radiation. We study the joint effect on the CO SLED excitation of (i) the X-ray luminosity from the AGN ($L_{X}$), (ii) the size of the molecular disk, (iii) the inclination angle ($\Omega$) of the torus with respect to the molecular disk, and (iv) the GMC mean density. We also discuss the possibility of an enhanced Cosmic Ray Ionization Rate (CRIR). We find that the X-ray Dominated Region (XDR) generated by the AGN in every case enhances the CO SLED for $J>5$, with increasing excitation of high-$J$ CO lines for increasing X-ray luminosity. Because high-$z$ galaxies are compact, the XDR region typically encloses the whole disk, thus its effect can be more important with respect to lower redshift objects. The impact of the XDR can be disentangled from an enhanced CRIR either if $L_X>10^{44} \rm \,erg\, s^{-1}$, or if $\Omega \geq 60^{\circ}$. We finally provide predictions on the CO(7-6)/[CII] and CO(17-16)/[CII] ratios as a function of $L_X$, which can be relevant for ALMA follow up of galaxies and quasars previously detected in [CII].


arXiv:1910.07553v1 [pdf, other]
The void halo mass function: a promising probe of neutrino mass
Comments: 5 pages, 2 figures

Cosmic voids, the underdense regions in the universe, are particularly sensitive to diffuse density components such as cosmic neutrinos. This sensitivity is enhanced by the match between void sizes and the free-streaming scale of massive neutrinos. Using the massive neutrino simulations \texttt{MassiveNuS}, we investigate the effect of neutrino mass on dark matter halos as a function of environment. We find that the halo mass function depends strongly on neutrino mass and that this dependence is more pronounced in voids than in high-density environments. An observational program that measured the characteristic mass of the most massive halos in voids should be able to place novel constraints on the sum of the masses of neutrinos $\sum m_\nu$. The neutrino mass effect in the simulations is quite strong: In a 512$^3$ $h^{-3}$ Mpc$^3$ survey, the mean mass of the 1000 most massive halos in the void interiors is $(4.82 \pm 0.11) \times 10^{12} h^{-1}M_{\odot}$ for $\sum m_\nu = 0.6$ eV and $(8.21 \pm 0.13) \times 10^{12} h^{-1}M_{\odot}$ for $\sum m_\nu = 0.1$ eV. Subaru (SuMIRe), Euclid and WFIRST will have both spectroscopic and weak lensing surveys. Covering volumes at least 50 times larger than our simulations, they should be sensitive probes of neutrino mass through void substructure.


arXiv:1910.07556v1 [pdf, other]
Direct collapse to supermassive black hole seeds: the critical conditions for suppression of $\rm H_2$ cooling
Comments: 10 pages, 5 figures, submitted to MNRAS

Observations of high-redshift quasars imply the presence of supermassive black holes already at z~ 7.5. An appealing and promising pathway to their formation is the direct collapse scenario of a primordial gas in atomic-cooling haloes at z ~ 10 - 20, when the $\rm H_2$ formation is inhibited by a strong background radiation field, whose intensity exceeds a critical value, $J_{\rm crit}$. To estimate $J_{\rm crit}$, idealized spectra have been assumed, with a fixed ratio of $\rm H_{2}$ photo-dissociation rate $k_{\rm H_2}$ to the $\rm H^-$ photo-detachment rate $k_{\rm H^-}$. This assumption, however, could be too narrow in scope as the nature of the background radiation field is not known precisely. In this work we show that the critical condition for suppressing the $\rm H_2$ cooling in the collapsing gas could be described in a more general way by a combination of $k_{\rm H_2}$ and $k_{\rm H^-}$ parameters. By performing a series of cosmological zoom-in simulations with an encompassing set of $k_{\rm H_2}$ and $k_{\rm H^-}$, we examine the gas flow by following evolution of basic parameters of the accretion flow. We test under what conditions the gas evolution is dominated by $\rm H_{2}$ and/or atomic cooling. We confirm the existence of a critical curve in the $k_{\rm H_2}-k_{\rm H^-}$ plane, and provide an analytical fit to it. This curve depends on the conditions in the direct collapse, and reveals domains where the atomic cooling dominates over the molecular cooling. Furthermore, we have considered the effect of $\rm H_{2}$ self-shielding on the critical curve, by adopting three methods for the effective column density approximation in $\rm H_{2}$. We find that the estimate of the characteristic length-scale for shielding can be improved by using $\lambda_{\rm Jeans25}$, which is 0.25 times that of the local Jeans length.


arXiv:1910.07559v1 [pdf, other]
The Nuclear Filaments inside the Circumnuclear Disk in the Central 0.5 pc of the Galactic center
Comments: 6 pages, 4 figures, accepted in ApJL

We present CS(7-6) line maps toward the central parsec of the Galactic Center (GC), conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The primary goal is to find and characterize the gas structure in the inner cavity of the circumnuclear disk (CND) in high resolution (1.3"=0.05 pc). Our large field-of-view mosaic maps -- combining interferometric and single-dish data that recover extended emission - provide a first homogeneous look to resolve and link the molecular streamers in the CND with the neutral nuclear filaments newly detected within the central cavity of the CND. We find that the nuclear filaments are rotating with Keplerian velocities in a nearly face-on orbit with an inclination angle of ~10-20 degree (radius <= 0.5 pc). This is in contrast to the CND which is highly inclined at ~65-80 degree (radius ~2-5 pc). Our analysis suggests a highly warped structure from the CND to the nuclear filaments. This result may hint that the nuclear filaments and the CND were created by different external clouds passing by Sgr A*.


arXiv:1910.07573v1 [pdf, other]
Resilient habitability of nearby exoplanet systems
Comments: 17 pages, 15 figures, comments welcome

We investigate the possibility of finding Earth-like planets in the habitable zone of 34 nearby FGK-dwarfs, each known to host one giant planet exterior to their habitable zone detected by RV. First we simulate the dynamics of the planetary systems in their present day configurations and determine the fraction of stable planetary orbits within their habitable zones. Then, we postulate that the eccentricity of the giant planet is a result of an instability in their past during which one or more other planets were ejected from the system. We simulate these scenarios and investigate whether planets orbiting in the habitable zone survive the instability. Explicitly we determine the fraction of test particles, originally found in the habitable zone, which remain in the habitable zone today. We label this fraction the resilient habitability of a system. We find that for most systems the probability of planets existing [or surviving] on stable orbits in the habitable zone becomes significantly smaller when we include a phase of instability in their history. We present a list of candidate systems with high resilient habitability for future observations. These are: HD 95872, HD 154345, HD 102843, HD 25015, GJ 328, HD 6718 and HD 150706. The known planets in the last two systems have large observational uncertainties on their eccentricities, which propagate into large uncertainties on their resilient habitability. Further observational constraints of these two eccentriciti


arXiv:1910.07574v1 [pdf, other]
Searching for scalar dark matter with compact mechanical resonators
Comments: No comment found

We explore the viability of laboratory-scale mechanical resonators as detectors for ultralight scalar dark matter. The signal we investigate is an atomic strain due to modulation of the fine structure constant and the lepton mass at the Compton frequency of dark matter particles. The resulting stress can drive an elastic body with acoustic breathing modes, producing displacements that are accessible with opto- or electromechanical readout techniques. To address the unknown mass of dark matter particles (which determines their Compton frequency), we consider various resonator designs operating at kHz to MHz frequencies, corresponding to $10^{-12}-10^{-5}$ eV particle mass. Current resonant-mass gravitational wave detectors that have been repurposed as dark matter detectors weigh $\sim \! 10^3$ kg. We find that a large unexplored parameter space can be accessed with ultra-high-$Q$, cryogenically-cooled, cm-scale mechanical resonators possessing $\sim \! 10^7$ times smaller mass.


arXiv:1910.07588v1 [pdf, other]
CHANG-ES XIV: Cosmic-ray propagation and magnetic field strengths in the radio halo of NGC 4631
Comments: 15 pages, 13 figures, accepted to be published in A&A

NGC 4631 is an interacting galaxy that exhibits one of the largest, gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and cosmic-ray propagation properties of its disk and halo emission with new radio continuum data. Radio continuum observations of NGC 4631 were performed with the Karl G. Jansky Very Large Array at C-band (5.99 GHz) in the C and D array configurations, and at L-band (1.57 GHz) in the B, C, and D array configurations. Complementary observations of NGC 4631 with the Effelsberg telescope were performed at 1.42 and 4.85 GHz. The interferometric total intensity data were combined with the single-dish Effelsberg data in order to recover the missing large-scale total power emission. The thermal and nonthermal components of the total radio emission were separated by estimating the thermal contribution through the extinction-corrected H$\alpha$ emission. The H$\alpha$ radiation was corrected for extinction using a linear combination of the observed H$\alpha$ and 24 $\mu$m data. NGC 4631 has a global thermal fraction at 5.99 (1.57) GHz of 14$\pm$3% (5.4$\pm$1.1%). The mean scale heights of the total emission in the radio halo (thick disk) at 5.99 (1.57) GHz are $1.79\pm0.54$ kpc ($1.75\pm0.27$ kpc) and have about the same values for the synchrotron emission. The total magnetic field of NGC 4631 has a mean strength of $\rm{\langle B_{eq}\rangle} \simeq 9 \rm{\mu G}$ in the disk, and a mean strength of $\rm{\langle B_{eq}\rangle}~\simeq 7~\rm{\mu G}$ in the halo. We also studied a double-lobed background radio galaxy southwest of NGC 4631, which is an FR~II radio galaxy according to the distribution of spectral index across the lobes. From the halo scale heights we estimated that the radio halo is escape-dominated with convective cosmic ray propagation, and conclude that there is a galactic wind in the halo of NGC 4631.


arXiv:1910.07590v1 [pdf, other]
CHANG-ES XV: Large-scale magnetic field reversals in the radio halo of NGC 4631
Comments: 8 pages, 7 figures, accepted to be published in A&A

NGC 4631 is an interacting galaxy which exhibits one of the largest gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and polarization properties of its disk and halo emission with new radio continuum data. Radio continuum observations of NGC 4631 were performed with the Karl G. Jansky Very Large Array at C-band (5.99 GHz) in the C & D array configurations, and at L-band (1.57 GHz) in the B, C, & D array configurations. The Rotation Measure Synthesis algorithm was utilized to derive the polarization properties. We detected linearly polarized emission at C-band and L-band. The magnetic field in the halo is characterized by strong vertical components above and below the central region of the galaxy. The magnetic field in the disk is only clearly seen in the eastern side of NGC 4631, where it is parallel to the plane of the major axis of the galaxy. We detected for the first time a large-scale, smooth Faraday depth pattern in a halo of an external spiral galaxy, which implies the existence of a regular (coherent) magnetic field. A quasi-periodic pattern in Faraday depth with field reversals was found in the northern halo of the galaxy. The field reversals in the northern halo of NGC 4631, together with the observed polarization angles, indicate giant magnetic ropes (GMRs) with alternating directions. To our knowledge, this is the first time such reversals are observed in an external galaxy.


arXiv:1910.07595v1 [pdf, other]
X-ray sources in Galactic globular clusters and old open clusters
Comments: 10 pages, to appear in the proceedings of IAU Symposium 351, "Star Clusters: From the Milky Way to the Early Universe", 2019

The features and make up of the population of X-ray sources in Galactic star clusters reflect the properties of the underlying stellar environment. Cluster age, mass, stellar encounter rate, binary frequency, metallicity, and maybe other properties as well, determine to what extent we can expect a contribution to the cluster X-ray emission from low-mass X-ray binaries, millisecond pulsars, cataclysmic variables, and magnetically active binaries. Sensitive X-ray observations with XMM-Newton and certainly Chandra have yielded new insights into the nature of individual sources and the effects of dynamical encounters. They have also provided a new perspective on the collective X-ray properties of clusters, in which the X-ray emissivities of globular clusters and old open clusters can be compared to each other and to those of other environments. I will review our current understanding of cluster X-ray sources, focusing on star clusters older than about 1 Gyr, illustrated with recent results.


arXiv:1910.07599v1 [pdf, other]
Wave heating from proto-neutron star convection and the core-collapse supernova explosion mechanism
Comments: 17 pages, 11 figures. Submitted to MNRAS

Our understanding of the core-collapse supernova explosion mechanism is incomplete. While the favoured scenario is delayed revival of the stalled shock by neutrino heating, it is difficult to reliably compute explosion outcomes and energies, which depend sensitively on the complex radiation hydrodynamics of the post-shock region. The dynamics of the (non-)explosion depend sensitively on how energy is transported from inside and near the proto-neutron star (PNS) to material just behind the supernova shock. Although most of the PNS energy is lost in the form of neutrinos, hydrodynamic and hydromagnetic waves can also carry energy from the PNS to the shock. We show that gravity waves excited by core PNS convection can couple with outgoing acoustic waves that present an appreciable source of energy and pressure in the post-shock region. Using one-dimensional simulations, we estimate the gravity wave energy flux excited by PNS convection and the fraction of this energy transmitted upward to the post-shock region as acoustic waves. We find wave energy fluxes near $10^{51}\,\mathrm{erg}\,\mathrm{s}^{-1}$ are likely to persist for $\sim1\,\mathrm{s}$ post-bounce. The wave pressure on the shock may exceed $10\%$ of the thermal pressure, potentially contributing to shock revival and, subsequently, a successful and energetic explosion. We also discuss how future simulations can better capture the effects of waves, and more accurately quantify wave heating rates.


arXiv:1910.07605v1 [pdf, other]
Near-Infrared Imaging of a Spiral in the CQ Tau Disk
Comments: submitted to AJ

We present $L^\prime$-band Keck/NIRC2 imaging and $H$-band Subaru/AO188+HiCIAO polarimetric observations of CQ Tau disk with a new spiral arm. Apart from the spiral feature our observations could not detect any companion candidates. We traced the spiral feature from the $r^2$-scaled HiCIAO polarimetric intensity image and the fitted result is used for forward modeling to reproduce the ADI-reduced NIRC2 image. We estimated the original surface brightness after throughput correction in $L^\prime$-band to be $\sim126$ mJy/arcsec$^2$ at most. The NIRC2 data correspond to an unexpectedly bright spiral that cannot simply be reproduced by scattered light, which suggests a hot spiral induced by a possible unseen protoplanet in the disk.


arXiv:1910.07619v1 [pdf, other]
Bow Magnetic Morphology Surrounding Filamentary Molecular Clouds? 3D Magnetic Field Structure of Orion-A
Comments: 11 pages, 15 Figures

Using a method based on Faraday rotation measurements, Tahani et al. 2018 find the line-of-sight component of magnetic fields in Orion-A and show that their direction changes from the eastern side of this filamentary structure to its western side. Three possible magnetic field morphologies that can explain this reversal across the Orion-A region are toroidal, helical, and bow-shaped morphologies. In this paper we construct simple models to represent these three morphologies and compare them with the available observational data to find the most probable morphology(ies). To compare the observations with the models, we use probability values and a Monte-Carlo analysis to determine the most likely magnetic field morphology among these three morphologies. We find that the bow morphology has the highest probability values and that our Monte-Carlo analysis suggests that the bow morphology is more likely. We suggest that the bow morphology is the most likely and the most natural of the three morphologies that could explain a magnetic field reversal across the Orion-A filamentary structure (i.e., bow, helical and toroidal morphologies).


arXiv:1910.07627v1 [pdf, other]
Observations and Preliminary Modeling of the Light Curves of Eclipsing Binary Systems NSVS 7322420 and NSVS 5726288
Comments: 10 pages, 9 figures, 4 tables, accepted for publication in the Journal of the American Association of Variable Star Observers

We present new photometric observations of the $\beta$ Lyrae-type eclipsing binary systems NSVS 7322420 and NSVS 5726288. These observations represent the first multi-band photometry performed on these systems. The light curves were analyzed with PHOEBE, a front-end GUI based on the Wilson-Devinney program, to produce models to describe our observations. Our preliminary solutions indicate that NSVS 7322420 is a primary filling semi-detached system with unusual features warranting further study. These features include a pronounced O'Connell effect, a temporal variance in the light curve, and an unusual "kink" in the light curve around the secondary eclipse. The cause of these features is unknown, but one possibility is the transfer of mass between the component stars. Meanwhile, NSVS 5726288 is probably a typical detached system.


arXiv:1910.07656v1 [pdf, other]
Correlated Depletion and Dilution of Lithium and Beryllium Revealed by Subgiants in M 67
Comments: 31 pages with 3 tables, 13 figures Accepted by Ap. J. 10/7/2019

The surface content of lithium (Li) and beryllium (Be) provide insights into the mixing and circulation mechanisms in stellar interiors. The old open cluster, M 67, has been well-studied for Li abundances in both main-sequence and evolved stars. The Be abundances give us a probe to a deeper level in stars. We have taken high-resolution spectra with Keck I with HIRES to determine Be abundances along the subgiant branch of M 67, where there are dramatic depletions of Li. These subgiants range in mass from 1.26 to 1.32 M$_{\odot}$ and have evolved from main-sequence stars that would have occupied the region of the Li-Be dip found in younger clusters. Lithium abundances have been adjusted to the same scale for 103 stars in M 67 by Pace et al. The more massive stars $-$ now the coolest and furthest-evolved from the main-sequence $-$ show a drop in Li by a factor of 400 across the subgiant branch. Our new Be abundances also show a decline, but by a factor of $\sim$50. The two elements decline together with Li showing a steeper decline in these subgiants than it does in the Li-Be dip stars. The relative decline in Be abundance compared to Li is remarkably well fit by the models of Sills & Deliyannis, made specifically for the subgiants in M 67. Those models include the effects of mixing induced by stellar rotation. These M 67 subgiants show the effects of both main-sequence depletion and post-main-sequence dilution of both Li and Be.


arXiv:1910.07664v1 [pdf, other]
Ellipticity of Brightest Cluster Galaxies as tracer of halo orientation and weak-lensing mass bias
Comments: 9 pages, 3 figures, 3 tables

Weak-lensing measurements of the masses of galaxy clusters are commonly based on the assumption of spherically symmetric density profiles. Yet, the cold dark matter model predicts the shapes of dark matter halos to be triaxial. Halo triaxiality, and the orientation of the major axis with respect to the line of sight, are expected to be the leading cause of intrinsic scatter in weak-lensing mass measurements. The shape of central cluster galaxies (Brightest Cluster Galaxies; BCGs) is expected to follow the shape of the dark matter halo. Here we investigate the use of BCG ellipticity as predictor of the weak-lensing mass bias in individual clusters compared to the mean. Using weak lensing masses $M^{\rm WL}_{500}$ from the Weighing the Giants project, and $M_{500}$ derived from gas masses as low-scatter mass proxy, we find that, on average, the lensing masses of clusters with the roundest / most elliptical 25% of BCGs are biased $\sim 20$% high / low compared to the average, as qualitatively predicted by the cold dark matter model. For cluster cosmology projects utilizing weak-lensing mass estimates, the shape of the BCG can thus contribute useful information on the effect of orientation bias in weak lensing mass estimates as well as on cluster selection bias.


arXiv:1910.07680v1 [pdf, other]
Search for Astronomical Neutrinos from Blazar TXS0506+056 in Super-Kamiokande
K. Hagiwara, K. Abe, C. Bronner, Y. Hayato, M. Ikeda, H. Ito, J. Kameda, Y. Kataoka, Y. Kato, Y. Kishimoto, Ll. Marti, M. Miura, S. Moriyama, T. Mochizuki, M. Nakahata, Y. Nakajima, S. Nakayama, T. Okada, K. Okamoto, A. Orii, G. Pronost, H. Sekiya, M. Shiozawa, Y. Sonoda, A. Takeda, A. Takenaka, H. Tanaka, T. Yano, R. Akutsu, T. Kajita, K. Okumura, R. Wang, J. Xia, D. Bravo-Bergu\no, L. Labarga, P. Fernandez, F. d. M. Blaszczyk, E. Kearns, J. L. Raaf, J. L. Stone, L. Wan, T. Wester, J. Bian, N. J. Griskevich, W. R. Kropp, S. Locke, S. Mine, M. B. Smy, H. W. Sobel, V. Takhistov, P. Weatherly, K. S. Ganezer, J. Hill, J. Y. Kim, I. T. Lim, R. G. Park, B. Bodur, K. Scholberg, C. W. Walter, A. Coffani, O. Drapier, M. Gonin, Th. A. Mueller, P. Paganini, T. Ishizuka, T. Nakamura, J. S. Jang, J. G. Learned, S. Matsuno, R. P. Litchfield, A. A. Sztuc, Y. Uchida, V. Berardi, N. F. Calabria, M. G. Catanesi, E. Radicioni, G. De Rosa, G. Collazuol, F. Iacob, L. Ludovici, Y. Nishimura, S. Cao, M. Friend, T. Hasegawa, T. Ishida, T. Kobayashi, T. Nakadaira, K. Nakamura, Y. Oyama, K. Sakashita, T. Sekiguchi, T. Tsukamoto, M. Hasegawa, Y. Isobe, H. Miyabe, Y. Nakano, T. Shiozawa, T. Sugimoto, A. T. Suzuki, Y. Takeuchi, A. Ali, Y. Ashida, S. Hirota, M. Jiang, T. Kikawa, M. Mori, KE. Nakamura, T. Nakaya, R. A. Wendell, L. H. V. Anthony, N. McCauley, A. Pritchard, K. M. Tsui, Y. Fukuda, Y. Itow, T. Niwa, M. Taani, M. Tsukada, P. Mijakowski, K. Frankiewicz, C. K. Jung, C. Vilela, M. J. Wilking, C. Yanagisawa, D. Fukuda, M. Harada, T. Horai, H. Ishino, S. Ito, Y. Koshio, M. Sakuda, Y. Takahira, C. Xu, Y. Kuno, L. Cook, C. Simpson, D. Wark, F. Di Lodovico, S. Molina Sedgwick, B. Richards, S. Zsoldos, S. B. Kim, M. Thiesse, L. Thompson, H. Okazawa, Y. Choi, K. Nishijima, M. Koshiba, M. Yokoyama, A. Goldsack, K. Martens, B. Quilain, Y. Suzuki, M. R. Vagins, M. Kuze, M. Tanaka, T. Yoshida, M. Ishitsuka, R. Matsumoto, K. Ohta, J. F. Martin, C. M. Nantais, H. A. Tanaka, T. Towstego, M. Hartz, A. Konaka, P. de Perio, S. Chen, B. Jamieson, J. Walker, A. Minamino, K. Okamoto, G. Pintaudi
Comments: No comment found

We report a search for astronomical neutrinos in the energy region from several GeV to TeV in the direction of the blazar TXS0506+056 using the Super-Kamiokande detector following the detection of a 100 TeV neutrino from the same location by the IceCube collaboration. Using Super-Kamiokande neutrino data across several data samples observed from April 1996 to February 2018 we have searched for both a total excess above known backgrounds across the entire period as well as localized excesses on smaller time scales in that interval. No significant excess nor significant variation in the observed event rate are found in the blazar direction. Upper limits are placed on the electron and muon neutrino fluxes at 90\% confidence level as $6.03 \times 10^{-7}$ and $4.52 \times 10^{-7}$ to $9.26 \times 10^{-10}$ [${\rm erg}/{\rm cm}^2/{\rm s}$], respectively.


arXiv:1910.07690v1 [pdf, other]
Evolution of the Deterministic Collapse Barrier of the Field Clusters as a Probe of Dark Energy
Comments: submitted for publication in ApJL, 6 figures, 1 table, comments welcome

The collapse barrier, $\delta_{c}$, of the field clusters located in the low-density environment is deterministic rather than diffusive, unlike that of the wall counterparts located in the superclusters. Analyzing the data from the Mira-Titan simulations for eleven different dark energy models including the $\Lambda$CDM cosmology at various redshifts, we investigate the evolution of the deterministic collapse barrier of the field clusters and explore its dependence on the background cosmology. Regardless of the background cosmology, the deterministic $\delta_{c}$ exhibits a universal behavior of having a higher value than the constant spherical collapse barrier height of $\delta_{sc}\approx 1.686$, at $z=0$ but gradually converging down to $\delta_{sc}$ as the dominance of dark energy diminishes with the increment of $z$. A significant difference among different dark energy models, however, is found in its convergence rate as well as in the critical redshift $z_{c}$ at which $\delta_{c}=\delta_{sc}$. Showing that the convergence rate and critical redshifts can distinguish even between the degenerate dark energy models which yield almost identical linear growth factor and cluster mass functions, we suggest that the evolution of the deterministic collapse barrier of the field clusters should be a powerful complementary probe of dark energy.


arXiv:1910.07691v1 [pdf, other]
Near-infrared Monitoring of the Accretion Outburst in the MYSO S255-NIRS3
Comments: 8 pages, 4 figures, 2 tables, accepted to PASJ

We followed-up the massive young stellar object (MYSO) S255-NIRS3 (=S255-IRS1b) during its recent accretion outburst event in the Ks band with Kanata/HONIR for four years after its burst and obtained a long-term light curve. This is the most complete NIR light-curve of the S255-NIRS3 burst event that has ever been presented. The light curve showed a steep increase reaching a peak flux that was 3.4 mag brighter than the quiescent phase and then a relatively moderate year-scale fading until the last observation, similar to that of the accretion burst events such as EXors found in lower-mass young stellar objects. The behavior of the Ks band light curve is similar to that observed in 6.7 GHz class II methanol maser emission, with a sudden increase followed by moderate year-scale fading. However, the maser emission peaks appear 30-50 days earlier than that of the Ks band emission. The similarities confirmed that the origins of the maser emission and the Ks band continuum emission is common as previously shown from another infrared and radio observations by Stecklum et al. (2016); Caratti o Garatti et al. (2017a); Moscadelli et al. (2017). However, the differences in energy transfer paths, such as the exciting/emitting/scattering structures, may cause the delay in the flux-peak dates.


arXiv:1910.07692v1 [pdf, other]
Assessing the Performance of Molecular Gas Clump Identification Algorithms
Comments: 23 pages, 13 figures. Accepted for publication in RAA

The detection of clumps(cores) in molecular clouds is an important issue in sub-millimetre astronomy. However, the completeness of the identification and the accuracy of the returned parameters of the automated clump identification algorithms are still not clear by now. In this work, we test the performance and bias of the GaussClumps, ClumpFind, Fellwalker, Reinhold, and Dendrograms algorithms in identifying simulated clumps. By designing the simulated clumps with various sizes, peak brightness, and crowdedness, we investigate the characteristics of the algorithms and their performance. In the aspect of detection completeness, Fellwalker, Dendrograms, and Gaussclumps are the first, second, and third best algorithms, respectively. The numbers of correct identifications of the six algorithms gradually increase as the size and SNR of the simulated clumps increase and they decrease as the crowdedness increases. In the aspect of the accuracy of retrieved parameters, Fellwalker and Dendrograms exhibit better performance than the other algorithms. The average deviations in clump parameters for all algorithms gradually increase as the size and SNR of clumps increase. Most of the algorithms except Fellwalker exhibit significant deviation in extracting the total flux of clumps. Taken altogether, Fellwalker, Gaussclumps, and Dendrograms exhibit the best performance in detection completeness and extracting parameters. The deviation in virial parameter for the six algorithms is relatively low. When applying the six algorithms to the clump identification for the Rosette molecular cloud, ClumpFind1994, ClumpFind2006, Gaussclumps, Fellwalker, and Reinhold exhibit performance that is consistent with the results from the simulated test.


arXiv:1910.07723v1 [pdf, other]
Detection of Late-Time Optical Emission from SN 1941C in NGC 4136
Comments: 7 pages, 5 figures

We report the detection of broad, high-velocity oxygen emission lines from the site of SN 1941C nearly eight decades after outburst, making it the oldest detected core-collapse supernova/youngest core-collapse supernova remnant with a well determined age. In contrast to the strongly blueshifted emission line profiles observed for all other late-time CCSNe thought to be due to dust extinction of rear hemisphere ejecta, SN 1941C's spectrum exhibits stronger redshifted than blueshifted emissions of [O I] 6300, 6364 [O II] 7319, 7330, and [O III] 4959, 5007. The oxygen emissions exhibit rest frame expansion velocities of -2200 to +4400 km/s. No other significant broad line emissions were detected including Halpha emission. We discuss possible causes for this unusual spectrum and compare SN 1941C's optical and X-ray luminosities to other evolved CCSNe.


arXiv:1910.07746v1 [pdf, other]
Formation of coronal rain triggered by impulsive heating associated with magnetic reconnection
Comments: 9 pages, 6 figures, accepted by A&A

Coronal rain consists of cool plasma condensations formed in coronal loops as a result of thermal instability. The standard models of coronal rain formation assume that the heating is quasi-steady and localised at the coronal loop footpoints. We present an observation of magnetic reconnection in the corona and the associated impulsive heating triggering formation of coronal rain condensations. We analyse combined SDO/AIA and IRIS observations of a coronal rain event following a reconnection between threads of a low-lying prominence flux rope and surrounding coronal field lines. The reconnection of the twisted flux rope and open field lines leads to a release of magnetic twist. Evolution of the emission of one of the coronal loops involved in the reconnection process in different AIA bandpasses suggests that the loop becomes thermally unstable and is subject to the formation of coronal rain condensations following the reconnection and that the associated heating is localised in the upper part of the loop leg. We conclude that in addition to the standard models of thermally unstable coronal loops with heating localised exclusively in the footpoints, thermal instability and subsequent formation of condensations can be triggered by the impulsive heating associated with magnetic reconnection occurring anywhere along a magnetic field line.


arXiv:1910.07754v1 [pdf, other]
Properties of local oscillations in the lower sunspot atmosphere
Comments: 13 pages, 9 figures, accepted to publication in ApJ, 2019

We present a study of wave processes in the sunspot region NOAA 12670 on 2017 August 10 observed by the Goode Solar Telescope in the TiO 7057 A and Ha 6563 A spectral lines. To study the distribution of power oscillations and their dynamics, we applied the pixelized wavelet filtering (PWF) technique. For the first time, the spatial structure of oscillation sources as a footpoints of fine magnetic tubes, anchored in the sunspot umbra was obtained. We found that at the chromosphere level, emission variation is a combination of numerous independent oscillations located in the sources with small angular size. Their spatial shape varies from dots and cellular in the umbra to filaments in the penumbra. Each narrow spectrum harmonic corresponds to its source, without global correlation among themselves. There is weak background as low-frequency oscillation sources are distributed on whole umbra. At the photosphere level we found regions with co-phased broadband oscillations of the whole umbra. Their spectrum includes the ~3-min harmonic, whose maximal value is localized in umbral dots (UDs), and the low frequency part near the ~5-min period. It is shown that the oscillation sources are displaced at different heights with increasing angular size. We assume that the observed spatial distribution of wave sources indicates the existence a slow subphotosphere resonator with a vertical magnetic field in the umbra and wave cutoff frequency due to inclination of the magnetic field line in the penumbra.


arXiv:1910.07760v1 [pdf, other]
What would happen if we were about 1 pc away from a supermassive black hole?
Comments: LaTex2e, 16 pages, no tables, 3 figures

We consider a hypothetic planet with the same mass $m$, radius $R$, angular momentum $\mathbf S$, oblateness $J_2$, semimajor axis $a$, eccentricity $e$, inclination $I$, and obliquity $\varepsilon$ of the Earth orbiting a main sequence star with the same mass $M_\star$ and radius $R_\star$ of the Sun at a distance $r_\bullet \simeq 1\,\mathrm{parsec}\,\left(\mathrm{pc}\right)$ from a supermassive black hole in the center of the hosting galaxy with the same mass $M_\bullet$ of, say, $\mathrm{M87}^\ast$. We preliminarily investigate some dynamical consequences of its presence in the neighbourhood of such a stellar system on the planet's possibility of sustaining complex life over the eons. In particular, we obtain general analytic expressions for the long-term rates of change, doubly averaged over both the planetary and the galactocentric orbital periods $P_\mathrm{b}$ and $P_\bullet$, of $e,\,I,\,\varepsilon$, which are the main quantities directly linked to the stellar insolation. We find that, for certain orbital configurations, the planet's perihelion distance $q=a\left(1-e\right)$ may greatly shrink leading, in some cases, even to an impact with the star. Also $I$ may notably change, with variations of the order even of tens of degrees. On the other hand, $\varepsilon$ does not seem to be particularly affected, being shifted, at most, by $\simeq 0.02\,\mathrm{deg}$ over a Myr. Our results strongly depend the eccentricity $e_\bullet$ of the galactocentric motion.


arXiv:1910.07793v1 [pdf, other]
My companion is bigger than your companion!
Comments: In press in The Observatory, February 2020 issue

We provide an analysis of the mass ratio distribution as gathered from almost all of the 559 orbital solutions derived by Professor Roger Griffin in his long series in the Observatory Magazine about "Spectroscopic Binary Orbits from Photoelectric Radial Velocities". The total distribution we determine is close to a uniform one, with a dearth of the smallest companions and an excess of almost twins. When splitting our sample between main-sequence and red giant primaries, however, we discover a different picture: the excess of twins is limited to the main-sequence stars, for which it appears even more pronounced. The mass-ratio distributions of red giants is characterised by a decline of systems with mass ratio above 0.6 and an excess of systems with a mass ratio around 0.25, which we attribute to post-mass transfer systems. The difference between the two mass-ratio distributions is likely due to the different primary masses they sample.


arXiv:1910.07803v1 [pdf, other]
Forward modeling of galaxy kinematics in slitless spectroscopy
Comments: 13 pages, accepted for publication in A&A

Slitless spectroscopy has long been considered as a complicated and confused technique. Nonetheless, with the advent of Hubble Space Telescope (HST) instruments characterized by a low sky background level and a high spatial resolution (most notably WFC3), slitless spectroscopy has become an adopted survey tool to study galaxy evolution from space. We investigate its application to single object studies to measure not only redshift and integrated spectral features, but also spatially resolved quantities such as galaxy kinematics. We build a complete forward model to be quantitatively compared to actual slitless observations. This model depends on a simplified thin cold disk galaxy description -- including flux distribution, intrinsic spectrum and kinematic parameters -- and on the instrumental signature. It is used to improve redshifts and constrain basic rotation curve parameters, i.e. plateau velocity $v_{0}$ (in $\rm km.s^{-1}$) and central velocity gradient $w_{0}$ (in $\rm km.s^{-1}.arcsec^{-1}$). The model is tested on selected observations from 3D-HST and GLASS surveys, to estimate redshift and kinematic parameters on several galaxies measured with one or more roll angles. Our forward approach allows to mitigate the self-contamination effect, a primary drawback of slitless spectroscopy, and therefore has the potential to increase precision on redshifts. In a limited sample of well-resolved spiral galaxies from HST surveys, it is possible to significantly constrain galaxy rotation curve parameters. This proof-of-concept work is promising for future large slitless spectroscopic surveys such as EUCLID and WFIRST.


arXiv:1910.07804v1 [pdf, other]
Spectral and Timing Properties of the Galactic X-ray transient Swift~J1658.2--4242 using Astrosat Observations
Comments: Accepted for Publication in ApJ, 13 Pages, 14 Figures, 3 Tables

We present the X-ray timing and spectral analysis of the new Galactic X-ray transient Swift J1658.2-4242 observed with LAXPC and SXT instruments onboard {\it Astrosat}. We detect prominent C-type quasi-periodic oscillations (QPOs) of frequencies varying from $\sim 1.5$ Hz to $\sim 6.6$ Hz along with distinct 2nd harmonics and sub-harmonics. The QPO detected at $\sim 1.56$ Hz drifts to a higher centroid frequency of $\sim 1.74$ in the course of the observation, while the QPO detected at $\sim 6.6$\,Hz disappeared during hard flarings. The fractional rms at the QPO and the sub-harmonic frequencies increases with photon energy, while at the 2nd harmonic frequencies the rms seems to be constant. In addition, we have observed soft time lag at QPO and sub-harmonic frequencies up to a time scale of $\sim 35$ ms, however, at the 2nd harmonic frequencies there is weak/zero time lag. We attempt spectral modeling of the broadband data in the 0.7--25 keV band using the doubly absorbed disk plus thermal Comptonization model. Based on the spectral and timing properties, we identified the source to be in the hard intermediate state of black hole X-ray binaries. To quantitatively fit the energy and frequency-dependent fractional rms and time lag, we use a single zone fluctuation propagation model and discuss our results in the context of that model.


arXiv:1910.07813v1 [pdf, other]
From Dark Matter to Galaxies with Convolutional Neural Networks
Comments: 5 pages, 2 figures. Accepted to the Second Workshop on Machine Learning and the Physical Sciences (NeurIPS 2019)

Cosmological simulations play an important role in the interpretation of astronomical data, in particular in comparing observed data to our theoretical expectations. However, to compare data with these simulations, the simulations in principle need to include gravity, magneto-hydrodyanmics, radiative transfer, etc. These ideal large-volume simulations (gravo-magneto-hydrodynamical) are incredibly computationally expensive which can cost tens of millions of CPU hours to run. In this paper, we propose a deep learning approach to map from the dark-matter-only simulation (computationally cheaper) to the galaxy distribution (from the much costlier cosmological simulation). The main challenge of this task is the high sparsity in the target galaxy distribution: space is mainly empty. We propose a cascade architecture composed of a classification filter followed by a regression procedure. We show that our result outperforms a state-of-the-art model used in the astronomical community, and provides a good trade-off between computational cost and prediction accuracy.


arXiv:1910.07818v1 [pdf, other]
Irregular changes in Hα emission line of V423 Aur observed by LAMOST Medium-Resolution Spectrographs
Comments: Accepted for publication in RAA

We obtained 7 spectra of the Be star V423 Aur on Dec. 5th, 2017 using the LAMOST Medium-Resolution Spectrograph with exposures from 600 to 1200 seconds. These spectra show the irregular H{\alpha} emission line profile variations (LPVs). In the seven spectra, from the 4th to 7th, the left part of H{\alpha} profile even show excess. However, no variation can be seen from the follow-up observation of photometry by 1.26-m telescope and High-Resolution spectra by 2.16-m telescope. According to the High-Resolution spectra, we conclude that it is a B7V type star with E(B-V)= 0.709{\pm}0.036 and its vsini is {\sim} 221.8km/s. The short-term H{\alpha} LPVs could be explained as a result of the transient ejection of matter from rotating disk or shell around V423 Aur.


arXiv:1910.07820v1 [pdf, other]
Quantifying Suspiciousness Within Correlated Data Sets
Comments: 7 pages, 4 figures

We propose a principled Bayesian method for quantifying tension between correlated datasets with wide uninformative parameter priors. This is achieved by extending the Suspiciousness statistic, which is insensitive to priors. Our method uses global summary statistics, and as such it can be used as a diagnostic for internal consistency. We show how our approach can be combined with methods that use parameter space and data space to identify the existing internal discrepancies. As an example, we use it to test the internal consistency of the KiDS-450 data in 4 photometric redshift bins, and to recover controlled internal discrepancies in simulated KiDS data. We propose this as a diagnostic of internal consistency for present and future cosmological surveys, and as a tension metric for data sets that have non-negligible correlation, such as LSST and Euclid.


arXiv:1910.07832v1 [pdf, other]
The interstellar medium content of galaxies in the ALMA era
Comments: 10 pages, 7 figures. Proceeding of IAU Symposium No. 352, 2019 "Uncovering early galaxy evolution in the ALMA and JWST era"

The advent of the Atacama Large Millimeter/submillimeter Array (ALMA) has enabled a new era for studies of the formation and assembly of distant galaxies. Cosmological deep field surveys with ALMA and other interferometers have flourished in the last few years covering wide ranges of galaxy properties and redshift, and allowing us to gain critical insights into the physical mechanisms behind the galaxy growth. Here, we present a brief review of recent studies that aim to characterize the interstellar medium properties of galaxies at high redshift ($z>1$), focusing on blank-field ALMA surveys of dust continuum and molecular line emission. In particular, we show recent results from the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) large program.


arXiv:1910.07835v1 [pdf, other]
Determining the mass of the planetary candidate HD 114762 b using Gaia
Comments: 4 figure, 4 tables, submitted to A&A on 17/10/2019

The first planetary candidate discovered with radial velocities around a solar-like star other than the Sun, HD 114762 b, by Latham et al. (1989) was detected with a minimum mass of 11 Mjup. The small v sin(i)~0 km/s otherwise measured by spectral analysis led to suspect that this companion of a late-F sub-giant star better correspond to a massive brown dwarf (BD), or even a low-mass M-dwarf nearly face-on. To our knowledge, the nature of HD 114762 b is still undetermined. Thanks to the first data release DR1 of the Gaia mission, the astrometric noise measured for this system allows us to derive new constraints on the astrometric motion of HD 114762 and on the mass of its companion. We use a method, GASTON, introduced in a preceding paper, able to simulate Gaia data and finding the distribution of inclinations compatible with the astrometric excess noise. With an inclination of 6.23(+1.93)(-1.25) degrees, the mass of the companion is constrained to M_b=107(+31)(-27) Mjup. HD 114762 b thus belong indeed to the M dwarf domain, down to brown dwarfs, with M_b>13.5 Mjup at the 3-sigma level, and is actually not a planet.


arXiv:1910.07855v1 [pdf, other]
Speeding simulation analysis up with yt and Intel Distribution for Python
Comments: 3 pages, 1 figure, published on Intel Parallel Universe Magazine

As modern scientific simulations grow ever more in size and complexity, even their analysis and post-processing becomes increasingly demanding, calling for the use of HPC resources and methods. yt is a parallel, open source post-processing python package for numerical simulations in astrophysics, made popular by its cross-format compatibility, its active community of developers and its integration with several other professional Python instruments. The Intel Distribution for Python enhances yt's performance and parallel scalability, through the optimization of lower-level libraries Numpy and Scipy, which make use of the optimized Intel Math Kernel Library (Intel-MKL) and the Intel MPI library for distributed computing. The library package yt is used for several analysis tasks, including integration of derived quantities, volumetric rendering, 2D phase plots, cosmological halo analysis and production of synthetic X-ray observation. In this paper, we provide a brief tutorial for the installation of yt and the Intel Distribution for Python, and the execution of each analysis task. Compared to the Anaconda python distribution, using the provided solution one can achieve net speedups up to 4.6x on Intel Xeon Scalable processors (codename Skylake).


arXiv:1910.07857v1 [pdf, other]
Chemical and kinematic structure of extremely high-velocity molecular jets in the Serpens Main star-forming region
Comments: 25 pages, 20 figures, Accepted for publication in the Astronomy & Astrophysics

The fastest molecular component to the protostellar outflows -- extremely high-velocity (EHV) molecular jets -- are still puzzling since they are seen only rarely. The first aim is to analyze the interaction between the EHV jet and the slow outflow by comparing their outflow force content. The second aim is to analyze the chemical composition of the different outflow velocity components and to reveal the spatial location of molecules. ALMA 3 mm and 1.3 mm observations of five outflow sources at 130 -- 260 au resolution in the Serpens Main cloud are presented. Observations of CO, SiO, H$_2$CO and HCN reveal the kinematic and chemical structure of those flows. Three velocity components are distinguished: the slow and the fast wing, and the EHV jet. Out of five sources, three have the EHV component. Comparison of outflow forces reveals that only the EHV jet in the youngest source Ser-emb 8 (N) has enough momentum to power the slow outflow. The SiO abundance is generally enhanced with velocity, while HCN is present in the slow and the fast wing, but disappears in the EHV jet. For Ser-emb 8 (N), HCN and SiO show a bow-shock shaped structure surrounding one of the EHV peaks suggesting sideways ejection creating secondary shocks upon interaction with the surroundings. Also, the SiO abundance in the EHV gas decreases with distance from this protostar, whereas that in the fast wing increases. H$_2$CO is mostly associated with low-velocity gas but also appears surprisingly in one of the bullets in the Ser-emb~8~(N) EHV jet. The high detection rate suggests that the presence of the EHV jet may be more common than previously expected. The origin and temporal evolution of the abundances of SiO, HCN and H$_2$CO through high-temperature chemistry are discussed. The data are consistent with a low C/O ratio in the EHV gas versus high C/O ratio in the fast and slow wings.


arXiv:1910.07865v1 [pdf, other]
ALMA observations of PKS 1549-79: a case of feeding and feedback in a young radio quasar
Comments: Accepted for A&A Main Journal

We present CO(1-0) and CO(3-2) ALMA observations of the molecular gas in PKS 1549-79, as well as mm and VLBI 2.3-GHz continuum observations of its radio jet. PKS 1549-79 is one of the closest young, radio-loud quasars caught in an on-going merger in which the AGN is in the first phases of its evolution. We detect three structures tracing the accretion and the outflow of molecular gas: kpc-scale tails of gas accreting onto PKS 1549-79, a circumnuclear disc (CND) in the inner few hundred parsec, and a very broad (>2300 \kms) component detected in CO(1-0) at the position of the AGN. Thus, in PKS 1549-79 we see the co-existence of accretion and the ejection of gas. The line ratio CO(1-0)/CO(3-2) suggests that the gas in the CND has both high densities and high kinetic temperatures. We estimate a mass outflow rate of at least 650 msun/yr. This massive outflow is confined to r < 120 pc, which suggests that the AGN drives the outflow. Considering the amount of molecular gas available in CND and the observed outflow rate, we estimate a time scale of ~10^5 yr over which the AGN would be able to destroy the CND, although gas from the merger may come in from larger radii, rebuilding this disc at the same time. The AGN appears to self-regulate gas accretion onto the super-massive black hole. From a comparison with HST data, we find that the ionised gas outflow is more extended. Nevertheless, the warm outflow is about two orders of magnitude less massive than the molecular outflow. PKS 1549-79 does not seem to follow the scaling relation between bolometric luminosity and the relative importance of warm ionised and molecular outflows claimed to exist for other AGN. We argue that, although PKS 1549-79 hosts a powerful quasar nucleus and an ultra-fast outflow, the radio jet plays a significant role in producing the outflow.


arXiv:1910.07868v1 [pdf, other]
Large-scale structures in the $Λ$CDM Universe: network analysis and machine learning
Comments: 10 pages, 11 figures, submitted to MNRAS

We perform an analysis of the Cosmic Web as a complex network, which is built on a $\Lambda$CDM cosmological simulation. For each of nodes, which are in this case dark matter halos formed in the simulation, we compute 10 network metrics, which characterize the role and position of a node in the network. The relation of these metrics to topological affiliation of the halo, i.e. to the type of large scale structure, which it belongs to, is then investigated. In particular, the correlation coefficients between network metrics and topology classes are computed. We have applied different machine learning methods to test the predictive power of obtained network metrics and to check if one could use network analysis as a tool for establishing topology of the large scale structure of the Universe. Results of such predictions, combined in the confusion matrix, show that it is not possible to give a good prediction of the topology of Cosmic Web (score is $\approx$ 70 $\%$ in average) based only on coordinates and velocities of nodes (halos), yet network metrics can give a hint about the topological landscape of matter distribution.


arXiv:1910.07940v1 [pdf, other]
First results from a large-scale proper motion study of the Galactic Centre
Comments: Accepted for publication in A&A. 13 pages, 17 figures

Proper motion studies of stars in the centre of the Milky Way have been typically limited to the Arches and Quintuplet clusters and to the central parsec. Here, we present the first results of a large-scale proper motion study of stars within several tens of parsecs of Sagittarius A* based on our $0.2''$ angular resolution GALACTICNUCLEUS survey (epoch 2015) combined with NICMOS/HST data from the Paschen-$\alpha$ survey (epoch 2008). This study will be the first extensive proper motion study of the central $\sim 36' \times 16'$ of the Galaxy, which is not covered adequately by any of the existing astronomical surveys such as Gaia because of its extreme interstellar extinction ($A_{V} \gtrsim 30$ mag). Proper motions can help us to disentangle the different stellar populations along the line-of-sight and interpret their properties in combination with multi-wavelength photometry from GALACTICNUCLEUS and other sources. It also allows us to infer the dynamics and interrelationship between the different stellar components of the Galactic Centre (GC). In particular, we use proper motions to detect co-moving groups of stars which can trace low mass or partially dissolved young clusters in the GC that can hardly be discovered by any other means. Our pilot study in this work is on a field in the nuclear bulge associated by HII regions that show the presence of young stars. We detect the first group of co-moving stars coincident with an HII region. Using colour-magnitude diagrams, we infer that the co-moving stars are consistent with being the post-main sequence stars with ages of few Myrs. Simulations show that this group of stars is a real group that can indicate the existence of a dissolving or low to intermediate mass young cluster. A census of these undiscovered clusters will ultimately help us to constrain star formation at the GC in the past few ten Myrs.


arXiv:1910.07941v1 [pdf, other]
Phase-resolved gamma-ray spectroscopy of the Crab pulsar observed by POLAR
Comments: 15 pages, 9 figures, 2 tables, accepted for publication in Journal of High Energy Astrophysics

The POLAR detector is a space based Gamma-Ray Burst (GRB) polarimeter sensitive in the 15-500 keV energy range. Apart from its main scientific goal as a Gamma-Ray Burst polarimeter it is also able to detect photons from pulsars in orbit. By using the six-months in-orbit observation data, significant pulsation from the PSR B0531+21 (Crab pulsar) was obtained. In this work, we present the precise timing analysis of the Crab pulsar, together with a phase-resolved spectroscopic study using a joint-fitting method adapted for wide field of view instruments like POLAR. By using single power law fitting over the pulsed phase, we obtained spectral indices ranging from 1.718 to 2.315, and confirmed the spectral evolution in a reverse S shape which is homogenous with results from other missions over broadband. We will also show, based on the POLAR in-orbit performance and Geant4 Monte-Carlo simulation, the inferred capabilities of POLAR-2, the proposed follow-up mission of POLAR on board the China Space Station (CSS), for pulsars studies.


arXiv:1910.07943v1 [pdf, other]
Chromospheric Synoptic Maps of Polar Crown Filaments
Comments: 18 pages, 10 figures

Polar crown filaments form above the polarity inversion line between the old magnetic flux of the previous cycle and the new magnetic flux of the current cycle. Studying their appearance and their properties can lead to a better understanding of the solar cycle. We use full-disk data of the Chromospheric Telescope (ChroTel) at the Observatorio del Teide, Tenerife, Spain, which were taken in three different chromospheric absorption lines (H-alpha 6563A, CaII-K 3933A, and HeI 10830A), and we create synoptic maps. In addition, the spectroscopic HeI data allow us to compute Doppler velocities and to create synoptic Doppler maps. ChroTel data cover the rising and decaying phase of Solar Cycle 24 on about 1000 days between 2012 and 2018. Based on these data, we automatically extract polar crown filaments with image-processing tools and study their properties. We compare contrast maps of polar crown filaments with those of quiet-Sun filaments. Furthermore, we present a super-synoptic map summarizing the entire ChroTel database. In summary, we provide statistical properties, i.e. number and location of filaments, area, and tilt angle for both the maximum and declining phase of Solar Cycle 24. This demonstrates that ChroTel provides a promising data set to study the solar cycle.


arXiv:1910.07956v1 [pdf, other]
Design, operation and performance of the PAON4 prototype transit interferometer
Comments: 17 pages, 16 figures, submitted to MNRAS

PAON4 is an L-band (1250-1500 MHz) small interferometer operating in transit mode deployed at the Nan\c{c}ay observatory in France, designed as a prototype instrument for Intensity Mapping. It features four 5 meter diameter dishes in a compact triangular configuration, with a total geometric collecting area of ~75m2, and equipped with dual polarisation receivers. A total of 36 visibilities are computed from the 8 independent RF signals by the software correlator over the full 250 MHz RF band. The array operates in transit mode, with the dishes pointed toward a fixed declination, while the sky drifts in front of the instrument. Sky maps for each frequency channel are then reconstructed by combining the time-dependent visibilities from the different baselines observed at different declinations. This paper presents an overview of the PAON4 instrument design and goals, as a prototype for dish arrays to map the Large Scale Structure in radio, using intensity mapping of the atomic hydrogen 21 cm line. We have operated PAON4 over several years and we have used data from observations in different periods to assess the array performances. We present preliminary analysis of a large fraction of this data and discuss crucial issues for this type of instrument, such as the calibration strategy, instrument response stability and noise behaviour.


arXiv:1910.07974v1 [pdf, other]
Detection of pulses from the Vela pulsar at millimeter wavelengths with phased ALMA
Comments: 8 pages, 6 figures, accepted for publication in ApJ letter

We report on the first detection of pulsed radio emission from a radio pulsar with the ALMA telescope. The detection was made in the Band-3 frequency range (85-101 GHz) using ALMA in the phased-array mode developed for VLBI observations. A software pipeline has been implemented to enable a regular pulsar observing mode in the future. We describe the pipeline and demonstrate the capability of ALMA to perform pulsar timing and searching. We also measure the flux density and polarization properties of the Vela pulsar (PSR J0835$-$4510) at mm-wavelengths, providing the first polarimetric study of any ordinary pulsar at frequencies above 32 GHz. Finally, we discuss the lessons learned from the Vela observations for future pulsar studies with ALMA, particularly for searches near the supermassive black hole in the Galactic Center, and the potential of using pulsars for polarization calibration of ALMA.


arXiv:1910.07977v1 [pdf, other]
POLAR measurements of the Crab pulsar
Comments: 8 pages, 7 figures, 1 table; PoS(ICRC 2017) 820

POLAR is a Compton polarimeter sensitive in the 50 to 500 keV energy range. The Crab pulsar is a scientific target for POLAR on board the Chinese space laboratory Tiangong-2 (TG-2). With its large Field of View (FoV), POLAR detected significant pulsed signals from the Crab pulsar which is visible by POLAR in about half of observation time. In this work, we present the preliminary results including the pulse profile, timing and polarization measuring method. First, we show the highly significant pulse profile observed by POLAR which is compared to the results of other detectors including Fermi/LAT and INTEGRAL. And the pulse profile as a function of theta incident angle and as a function of channel number, which indicate that POLAR has a good detection performance, have been showed. Second, we find that the timing of the Crab pulses are accurately measured, which provides a unique verification and calibration to the POLAR timing system. Finally, the potential polarization measurement of the Crab pulsar is also discussed.


arXiv:1910.07981v1 [pdf, other]
Mass bound for primordial black hole from trans-Planckian censorship conjecture
Comments: 6 pages, 2 figures, two columns

The recently proposed trans-Planckian censorship conjecture (TCC) imposes a strong constraint on the inflationary Hubble scale, of which the upper bound could be largely relaxed by considering a non-instantaneous reheating history. In this letter we will show that, if the primordial black holes (PBHs) are collapsed at reentry in the radiation-dominated era from the enhanced curvature perturbations at small scales, the TCC would impose a lower bound on the PBH mass $M_\mathrm{PBH}>\gamma(H_\mathrm{end}/10^9\,\mathrm{GeV})^2\,M_\odot$ regardless of the detail for reheating history, where $\gamma$ is the collapse efficiency factor and $H_\mathrm{end}$ is the Hubble scale at the end of inflation. In particular, the current open window for PBHs to make up all the cold dark matter could be totally ruled out if the inflationary Hubble scale is larger than 10 TeV. For the case of PBHs formed in an early matter-dominated era, an upper mass bound is obtained.


arXiv:1910.07996v1 [pdf, other]
Measurements of Low Temperature Rate Coefficients for the Reaction of CH with CH$_{2}$O and Application to Dark Cloud and AGB Stellar Wind Models
Comments: 17 pages, 9 Figures, 5 Tables, Accepted for publication in The Astrophysical Journal

Rate coefficients have been measured for the reaction of CH radicals with formaldehyde, CH$_{2}$O, over the temperature range 31 - 133 K using a pulsed Laval nozzle apparatus combined with pulsed laser photolysis and laser induced fluorescence spectroscopy. The rate coefficients are very large and display a distinct decrease with decreasing temperature below 70 K, although classical collision rate theory fails to reproduce this temperature dependence. The measured rate coefficients have been parameterized and used as input for astrochemical models for both dark cloud and AGB stellar outflow scenarios. The models predict a distinct change (up to a factor of two) in the abundance of ketene, H$_{2}$CCO, which is the major expected molecular product of the CH + CH$_{2}$O reaction.


arXiv:1910.08005v1 [pdf, other]
Fingerprints of the protosolar cloud collapse in the Solar System I: Distribution of presolar short-lived $^{26}$Al
Comments: ArXiv version

The short-lived radionuclide $^{26}$Al is widely used to determine the relative ages of chondrite components and timescales of physical and thermal events that attended the formation of the Solar System. However, an important assumption for using $^{26}$Al as a chronometer is its homogeneous distribution in the disk. Yet, the oldest components in chondrites, the Ca-Al-rich inclusions (CAIs), which are usually considered as time anchors for this chronometer, show evidence of $^{26}$Al/$^{27}$Al variations independent of radioactive decay. Since their formation epoch may have been contemporaneous with the collapse of the parent cloud that formed the disk, this suggests that $^{26}$Al was heteregeneously distributed in the cloud. We model the collapse of such an heterogeneous cloud, using two different $^{26}$Al distributions (monotonic and non-monotonic), and follow its re-distribution in the first condensates and bulk dust that populate the forming disk. We find that CAIs inherit the $^{26}$Al/$^{27}$Al ratio of the matter infalling at the time of their formation, so that variations of $^{26}$Al/$^{27}$Al among primordial CAIs can be accounted for, independently of radioactive decay. The prevalence of a canonical ratio among them and its necessity for the differentiation of the first planetesimals suggest a (monotonic) scenario where $^{26}$Al sharply rose relatively close to the center of the protosolar cloud and essentially remained at a high level outward (rather than decreased since). As the $ ^{26}$Al abundance would be relatively homogeneous after cessation of infall, this would warrant the use of the Al-Mg chronometer from the formation of "regular" CAIs onward, to chondrules and chondrite accretion.


arXiv:1910.08017v1 [pdf, other]
Edge-on galaxies in the Hubble Ultra Deep Field
Comments: 10 pages, 6 figures

We studied a sample of 58 edge-on spiral galaxies at redshifts $z \sim 1$ selected in the Hubble Ultra Deep Field. For all galaxies we analyzed the 2D brightness distributions in the $V_{606}$ and $i_{775}$ filters and measured the radial ($h_r$) and vertical ($h_z$) exponential scales of the brightness distribution. We obtained evidence that the relative thickness of the disks of distant galaxies, i.e., the ratio of the vertical scale height and radial scale length ($h_z/h_r$), on average, exceeds the relative thickness of the disks of nearby spiral galaxies. The vertical scale height $h_z$ of the stellar disks of galaxies shows no big changes at $z \leq 1$. The possibility of the evolution of the radial scale length $h_r$ for the brightness distribution with redshift is discussed.


arXiv:1910.08021v1 [pdf, other]
Enhanced mass-loss rate evolution of stars with $\gtrsim 18 M_\odot$ and missing optically-observed type II core-collapse supernovae
Comments: Will be submitted in a few days to allow comments by readers

We evolve stellar models with zero age main sequence (ZAMS) mass of $M_{\rm ZAMS} \gtrsim 18 M_\odot$ under the assumption that they experience an enhanced mass-loss rate when crossing the instability strip at high luminosities, and conclude that most of them end as type Ibc supernovae (SNe Ibc) or dust-obscured SNe II. We examine the hydrogen mass in the stellar envelope and the optical depth of the dusty wind at explosion, and crudely estimate that only about a fifth of these stars explode as unobscured SNe II and SNe IIb. About 10-15 percent end as obscured SNe II that are infrared-bright but visibly very faint, and the rest, about 65-70 percent end as SNe Ibc. Our findings have implications to the 'red supergiant problem', referring to the death of observed core-collapse supernovae with $M_{\rm ZAMS} \gtrsim 18 M_\odot$, as we conclude that it is possible that all these stars actually do explode as CCSNe. However, the statistical uncertainties are still too large to decide whether many stars with $M_{\rm ZAMS} \gtrsim 18M_\odot$ do not explode as expected in the neutrino driven explosion mechanism, or whether all of them explode as CCSNe, as expected by the jittering jets explosion mechanism.


arXiv:1910.08027v1 [pdf, other]
A 3D radiation-hydrodynamic AGB binary model
Comments: 20 pages, 10 figures, and 4 tables. Submitted to the ApJ

The origin of the chemically peculiar stars and non-zero eccentricity in evolved close binaries have been long-standing problems in stellar evolution. Answers to these questions may trace back to an intense mass transfer phase. In this work, we use AstroBEAR to solve the 3D radiation-hydrodynamic equations and calculate the mass transfer rate in asymptotic-giant-branch (AGB) binaries that undergo the wind-Roche-lobe-overflow or Bondi-Hoyle-Lyttleton (BHL) accretion. To resolve the dynamics of a circumbinary disk, we implement an azimuthal angle-dependent 3D radiation transfer. We consider optically thin cooling and obtain the number density of the coolants by solving the Saha equation. We use MESA to produce the density and temperature of the boundary condition of the AGB star. Four simulations are carried out to illustrate the transition from the wind-Roche-lobe-overflow to BHL accretion. Both circumbinary disks and spiral structure outflows can appear in the simulations. The resulting mass transfer efficiency in our models is up to a factor of eight times higher than what the standard BHL accretion scenario predicts, and the outflow gains up to $91\%$ of its initial angular momentum when it reaches 1.3 binary separations. Consequently, some AGB binaries may undergo orbit shrinkage, and some will expand. The mass transfer efficiency is closely related to the presence of the circumbinary disks. Circumbinary disks may form when the optical thickness in the equatorial region becomes greater than a critical value. The increase of the optical thickness is due to the deflected wind.


arXiv:1910.08028v1 [pdf, other]
ESA Voyage 2050 white paper -- Faint objects in motion: the new frontier of high precision astrometry
Comments: White paper for the Voyage 2050 long-term plan in the ESA Science Programme. arXiv admin note: substantial text overlap with arXiv:1707.01348

Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of earth-massed habitable worlds around the nearest starts, and also into distant Milky way objects up to the Local Group of galaxies. As we enter the era of the James Webb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry ESA missions: NEAT for M3, micro-NEAT for S1 mission, and Theia for M4 and M5. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this white paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review quickly instrumentation and mission profiles.


arXiv:1910.08034v1 [pdf, other]
LcTools: A Windows-Based Software System for Finding and Recording Signals in Lightcurves from NASA Space Missions
Comments: 28 pages, 31 figures, arXiv-only submission

Since 2009, the Kepler, K2, and TESS missions have produced a vast number of lightcurves for public use. To assist citizen scientists in processing those lightcurves, the LcTools software system was developed. The system provides a set of tools to efficiently search for signals of interest in large sets of lightcurves using automated and manual (visual) techniques. At the heart of the system is a multipurpose lightcurve viewer and signal processor with advanced navigation and display capabilities to facilitate the search for signals. Other applications in the system are available for building lightcurve files in bulk, finding periodic signals automatically, and generating signal reports. This paper describes each application in the system and the methods by which the software can be used to detect and record signals. The software is free and can be obtained from the lead author by request.


arXiv:1910.08043v1 [pdf, other]
Novel pre-burst stage of gamma-ray bursts from machine learning
Comments: 12 latex pages, 12 figures

Gamma-ray bursts (GRBs), as extremely energetic explosions in the universe, are widely believed to consist of two stages: the prompt phase and the subsequent afterglow. Recent studies indicate that some high-energy photons are emitted earlier at source than the prompt phase. Due to the light speed variation, these high-energy photons travel slowly than the low-energy photons, so that they are observed after the prompt low-energy photons at the detector. Based on the data from the Fermi Gamma-ray Space Telescope (FGST), we analyse the photon distribution before the prompt emission in detail and propose the existence of a hitherto unknown pre-burst stage of GRBs by adopting a classification method of machine learning. Analysis on the photons automatically selected by machine learning also produce a light speed variation at $E_{\mathrm{LV}}=\mathrm{3.55\times 10^{17} GeV}$.


arXiv:1910.08046v1 [pdf, other]
The impact of the locally measured Hubble parameter on the mass of Sterile neutrino
Comments: 8 pages, 4 figures

We present a precise analysis to test hypothetical models involving sterile neutrinos beyond the standard flat-$\Lambda$CDM cosmology with the CMB observations from the $Planck$ mission and BAO measurements. This analysis shows that adding the locally measured Hubble parameter $H_{0}$ = $73.00\pm1.75 $ km $\textrm s^{-1}$ Mp$\textrm c^{-1} $ to the data removes the need for the informative physical $m_{sterile}^{thermal}$ prior in CMB constraints of $ m_{\nu,sterile}^{eff}$. Under the constraints from the data containing the locally measured $H_{0}$ we obtain an upper limit $ m_{\nu,sterile}^{eff} < 0.306 $ eV scale mass for the massive sterile neutrino, and an upper limit $\Sigma m_{\nu} < 0.214$ eV scale mass for the three degenerate massive neutrino (95 per cent confidence level). We also obtain the value $\sigma_{8} $ = $0.81^{+0.05}_{-0.06} $ (95 per cent confidence level), which is in compatibility with the constraints from $Planck$ 2015 CMB data at the 1$\sigma$ level. We find that introducing parameter $ m_{\nu,sterile}^{eff}$ to the model of cosmology reduces the $\sigma_{8} $ value and moves it closer to the obtained value for this parameter from the KiDS-450 analysis. Our results show that the locally measured Hubble parameter can increase constraints on $\sigma_{8} $ values.


arXiv:1910.08052v1 [pdf, other]
Measuring the net circular polarization of the stochastic gravitational wave background with interferometers
Comments: 33 pages + appendices, 6 figures

Parity violating interactions in the early Universe can source a stochastic gravitational wave background (SGWB) with a net circular polarization. In this paper, we study possible ways to search for circular polarization of the SGWB with interferometers. Planar detectors are unable to measure the net circular polarization of an isotropic SGWB. We discuss the possibility of using the dipolar anisotropy kinematically induced by the motion of the solar system with respect to the cosmic reference frame to measure the net circular polarization of the SGWB with planar detectors. We apply this approach to LISA, re-assessing previous analyses by means of a more detailed computation and using the most recent instrument specifications, and to the Einstein Telescope (ET), estimating for the first time its sensitivity to circular polarization. We find that both LISA and ET, despite operating at different frequencies, could detect net circular polarization with a signal-to-noise ratio of order one in a SGWB with amplitude $h^2 \Omega_\text{GW} \simeq 10^{-11}$. We also investigate the case of a network of ground based detectors. We present fully analytical, covariant formulas for the detector overlap functions in the presence of circular polarization. Our formulas do not rely on particular choices of reference frame, and can be applied to interferometers with arbitrary angles among their arms.


arXiv:1910.08053v1 [pdf, other]
Predicting the Extreme Ultraviolet Radiation Environment of Exoplanets Around Low-Mass Stars: GJ 832, GJ 176, GJ 436
Comments: 21 pages, 12 figures, accepted to ApJ

Correct estimates of stellar extreme ultraviolet (EUV; 100 - 1170 \AA) flux are important for studying the photochemistry and stability of exoplanet atmospheres, as EUV radiation ionizes hydrogen and contributes to the heating, expansion, and potential escape of a planet's upper atmosphere. Contamination from interstellar hydrogen makes observing EUV emission from M stars particularly difficult, and impossible past 100 pc, and necessitates other means to predict the flux in this wavelength regime. We present EUV -- infrared (100 \AA - 5.5 $\mu$m) synthetic spectra computed with the PHOENIX atmospheric code of three early M dwarf planet hosts: GJ 832 (M1.5 V), GJ 176 (M2.5 V), and GJ 436 (M3.5 V). These one-dimensional semiempirical nonlocal thermodynamic equilibrium models include simple temperature prescriptions for the stellar chromosphere and transition region, from where ultraviolet (UV; 100 - 3008 \AA) fluxes originate. We guide our models with Hubble Space Telescope far- and near-UV spectra and discuss the ability to constrain these models using Galaxy Evolution Explorer UV photometry. Our models closely reproduce the observations and predict the unobservable EUV spectrum at a wavelength resolution of < 0.1 \AA. The temperature profiles that best reproduce the observations for all three stars are described by nearly the same set of parameters, suggesting that early M type stars may have similar thermal structures in their upper atmospheres. With an impending UV observation gap and the scarcity of observed EUV spectra for stars less luminous and more distant than the Sun, upper-atmosphere models such as these are important for providing realistic spectra across short wavelengths and for advancing our understanding of the effects of radiation on planets orbiting M stars.


arXiv:1910.08066v1 [pdf, other]
The impact of the connectivity of the cosmic web on the physical properties of galaxies at its nodes
Comments: 16 pages, 15 figures, submitted to MNRAS

We investigate the impact of the number of filaments connected to the nodes of the cosmic web on the physical properties of their galaxies using the Sloan Digital Sky Survey. We compare these measurements to the cosmological hydrodynamical simulations Horizon-(no)AGN and Simba. We find that more massive galaxies are more connected, in qualitative agreement with theoretical predictions and measurements in dark matter only simulation. The star formation activity and morphology of observed galaxies both display some dependence on the connectivity of the cosmic web at fixed stellar mass: less star forming and less rotation supported galaxies also tend to have higher connectivity. These results qualitatively hold both for observed and virtual galaxies, and can be understood given that the cosmic web is the main source of fuel for galaxy growth. The simulations show the same trends at fixed halo mass, suggesting that the geometry of filamentary infall impacts galaxy properties beyond the depth of the local potential well. Based on simulations, it is also found that AGN feedback is key in reversing the relationship between stellar mass and connectivity at fixed halo mass. Technically, connectivity is a practical observational proxy for past and present accretion (minor mergers or diffuse infall).