Ferah Munshi

REPRODUCING THE STELLAR MASS/HALO MASS RELATION IN SIMULATED ΛCDM GALAXIES: THEORY VERSUS OBSERVATIONAL ESTIMATES

We examine the present-day total stellar-to-halo mass (SHM) ratio as a function of halo mass for a new sample of simulated field galaxies using fully cosmological, ?CDM, high-resolution SPH + N-body simulations. These simulations include an explicit treatment of metal line cooling, dust and self-shielding, H2-based star formation (SF), and supernova-driven gas outflows. The 18 simulated halos have masses ranging from a few times 108 to nearly 1012 M ?. At z = 0, our simulated galaxies have a baryon content and morphology typical of field galaxies. Over a stellar mass range of 2.2 ? 103-4.5 ? 1010 M ? we find extremely good agreement between the SHM ratio in simulations and the present-day predictions from the statistical abundance matching technique presented in Moster et?al. This improvement over past simulations is due to a number systematic factors, each decreasing the SHM ratios: (1) gas outflows that reduce the overall SF efficiency but allow for the formation of a cold gas component; (2)?estimating the stellar masses of simulated galaxies using artificial observations and photometric techniques similar to those used in observations; and (3) accounting for a systematic, up to 30% overestimate in total halo masses in DM-only simulations, due to the neglect of baryon loss over cosmic times. Our analysis suggests that stellar mass estimates based on photometric magnitudes can underestimate the contribution of old stellar populations to the total stellar mass, leading to stellar mass errors of up to 50% for individual galaxies. These results highlight that implementing a realistic high density threshold for SF considerably reduces the overall SF efficiency due to more effective feedback. However, we show that in order to reduce the perceived tension between the SF efficiency in galaxy formation models and in real galaxies, it is very important to use proper techniques to compare simulations with observations.

IN-N-OUT: The GAS CYCLE from DWARFS to SPIRAL GALAXIES

We examine the scalings of galactic outflows with halo mass across a suite of twenty high-resolution cosmological zoom galaxy simulations covering halo masses from 10^9.5 - 10^12 M_sun. These simulations self-consistently generate outflows from the available supernova energy in a manner that successfully reproduces key galaxy observables including the stellar mass-halo mass, Tully-Fisher, and mass-metallicity relations. We quantify the importance of ejective feedback to setting the stellar mass relative to the efficiency of gas accretion and star formation. Ejective feedback is increasingly important as galaxy mass decreases; we find an effective mass loading factor that scales as v_circ^(-2.2), with an amplitude and shape that is invariant with redshift. These scalings are consistent with analytic models for energy-driven wind, based solely on the halo potential. Recycling is common: about half the outflow mass across all galaxy masses is later re-accreted. The recycling timescale is typically about 1 Gyr, virtually independent of halo mass. Recycled material is re-accreted farther out in the disk and with typically about 2-3 times more angular momentum. These results elucidate and quantify how the baryon cycle plausibly regulates star formation and alters the angular momentum distribution of disk material across the halo mass range where most of cosmic star formation occurs.

Effects of inclination on measuring velocity dispersion and implications for black holes

The relation of central black hole mass and stellar spheroid velocity dispersion (the M-

The Pressure of the Star-forming Interstellar Medium in Cosmological Simulations

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Multimessenger Signatures of Massive Black Holes in Dwarf Galaxies

relation) is one of the best-known and tightest correlations linking black holes and their host galaxies. There has been much scrutiny concerning the difficulty of obtaining accurate black hole measurements, and rightly so; however, it has been taken for granted that measurements of velocity dispersion are essentially straightforward. We examine five disk galaxies from cosmological SPH simulations and find that line-of-sight effects due to galaxy orientation can affect the measured

The Very Short Period M Dwarf Binary SDSS J001641–000925

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by 30%, and consequently black hole mass predictions by up to 1.0 dex. Face-on orientations correspond to systematically lower velocity dispersion measurements, while more edge-on orientations give higher velocity dispersions, due to contamination by disk stars when measuring line of sight quantities. We caution observers that the uncertainty of velocity dispersion measurements is at least 20 km/s, and can be much larger for moderate inclinations. This effect may account for some of the scatter in the locally measured M-

Going, going, gone dark: Quantifying the scatter in the faintest dwarf galaxies

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ERRATUM: “THE PRESSURE OF THE STAR-FORMING ISM IN COSMOLOGICAL SIMULATIONS” (2014, ApJL, 781, L14)

relation, particularly at the low-mass end. We provide a method for correcting observed

Testing the Effectiveness of the H-alpha/UV flux Ratio in Determining Star Formation Rates in Dwarf Galaxies

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