Day 1622

Monday.

1908.11380
The quenching and morphological evolution of central galaxies is facilitated by the feedback-driven expulsion of circumgalactic gas
Davies, et al

We examine the connection between the properties of the circumgalactic medium (CGM) and the quenching and morphological evolution of central galaxies in the EAGLE and IllustrisTNG simulations. The simulations yield very different median CGM mass fractions, $f_{\rm CGM}$, as a function of halo mass, $M_{200}$, with low-mass haloes being significantly more gas-rich in IllustrisTNG than in EAGLE. Nonetheless, in both cases scatter in $f_{\rm CGM}$ at fixed $M_{200}$ is strongly correlated with the specific star formation rate and the kinematic morphology of central galaxies. The correlations are strongest for $\sim L^\star$ galaxies, corresponding to the mass scale at which expulsive AGN feedback becomes efficient. This feedback elevates the CGM cooling time, preventing gas from accreting onto the galaxy to fuel star formation, and thus establishing a preference for quenched, spheroidal galaxies to be hosted by haloes with low $f_{\rm CGM}$ for their mass. In both simulations, $f_{\rm CGM}$ correlates negatively with the host halo's intrinsic concentration, and hence with its binding energy and formation redshift, primarily because early halo formation fosters the rapid early growth of the central black hole (BH). This leads to a lower $f_{\rm CGM}$ at fixed $M_{200}$ in EAGLE because the BH reaches high accretion rates sooner, whilst in IllustrisTNG it occurs because the central BH reaches the mass threshold at which AGN feedback is assumed to switch from thermal to kinetic injection earlier. Despite these differences, there is consensus from these state-of-the-art simulations that the expulsion of efficiently-cooling gas from the CGM is a crucial step in the quenching and morphological evolution of central galaxies.

1908.11392

VEXAS: the VISTA Extension to Auxiliary Surveys -- Data Release 1: the Southern Galactic Hemisphere

Spiniello, Agnello

We present the first public data release of the VISTA EXtension to Auxiliary Surveys (VEXAS), comprising of 9 cross-matched multi-wavelength photometric catalogs where each object has a match in at least two surveys. We aim at a spatial coverage as uniform as possible in the multi-wavelength sky, with the purpose of providing the astronomical community with reference magnitudes and colours for various scientific uses, including: object classification (e.g. quasars, galaxies, and stars; high-z galaxies, white dwarfs, etc.); photometric redshifts of large galaxy samples; searches of exotic objects such as, for example, extremely red objects and lensed quasars. We have cross-matched the wide-field VISTA catalogs (the VISTA Hemisphere Survey and the VISTA Kilo Degree Infrared Galaxy Survey) with the AllWISE mid-infrared Survey, requiring that a match exists within 10 arcsec. We have further matched this table with X-Ray and radio data (ROSAT, XMM, SUMSS). We also performed a second cross-match between VISTA and AllWISE, with a smaller matching radius (3"), including WISE magnitudes. We have then cross-matched this resulting table ($\approx138\times10^6$ objects) with three photometric wide-sky optical deep surveys (DES, SkyMapper, PanSTARRS). We finally include matches to objects with spectroscopic follow-up by the SDSS and 6dFGS. To demonstrate the power of all-sky multi-wavelength cross-match tables, we show two examples of scientific applications of VEXAS, in particular using the publicly released tables to discover strong gravitational lenses (beyond the reach of previous searches), and to build a statistically large sample of extremely red objects. The VEXAS catalog is currently the widest and deepest, public, optical-to-IR photometric and spectroscopic database in the Southern Hemisphere.

1908.11440

Radio flares from collisions of neutrino stars with interstellar asteroids

Siraj, Loeb

We propose that collisions between neutron stars and interstellar asteroids, such as `Oumuamua, could power observable radio flares in the Milky Way galaxy. We find the rate of such events at $\sim 1 \mathrm{\; Jy}$ to be $\sim 10 \mathrm{\; day^{-1}}$.

1908.11448

Testing the accuracy of halo occupation distribution modeling using hydrodynamic simulations

Beltz-Mohrmann, et al

Halo models provide a simple and computationally inexpensive way to investigate the connection between galaxies and their dark matter haloes. However, these models rely on the assumption that the role of baryons can be easily parametrized in the modelling procedure. We aim to examine the ability of halo occupation distribution (HOD) modelling to reproduce the galaxy clustering found in two different hydrodynamic simulations, Illustris and EAGLE. For each simulation, we measure several galaxy clustering statistics on two different luminosity threshold samples. We then apply a simple five parameter HOD, which was fit to each simulation separately, to the corresponding dark matter only simulations, and measure the same clustering statistics. We find that the halo mass function is shifted to lower masses in the hydrodynamic simulations, resulting in a galaxy number density that is too high when an HOD is applied to the dark matter only simulation. However, the exact way in which baryons alter the mass function is remarkably different in the two simulations. After applying a correction to the halo mass function in each simulation, the HOD is able to accurately reproduce all clustering statistics for the high luminosity sample of galaxies. For the low luminosity sample, we find evidence that in addition to correcting the halo mass function, including spatial, velocity, and assembly bias parameters in the HOD is necessary to accurately reproduce clustering statistics.