AbstractsAstronomy & Space Science

Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

by Coral Rose Wheeler

Institution: University of California – Irvine
Year: 2016
Keywords: Astrophysics; Astronomy; dwarf galaxies; galactic dynamics; galaxies; Local Group; star formation
Posted: 02/05/2017
Record ID: 2081625
Full text PDF: http://www.escholarship.org/uc/item/06x8m9xw


We study dwarf satellite galaxy quenching using observations from the Geha et al. (2012) NSA/SDSS catalog together with CDM cosmological simulations to facilitate selection and interpretation. We show that fewer than 30% of dwarfs (M* ~ 108.5-109.5 Msun) identified as satellites within massive host halos (Mhost ~ 1012.5-1014 Msun) are quenched. We conclude that whatever the action triggering environmental quenching of dwarf satellites, the process must be highly inefficient. We investigate a series of simple, one-parameter quenching models in order to understand what is required to explain the low quenched fraction and conclude that either the quenching timescale is very long (> 9.5 Gyr, a “slow starvation” scenario) or that the environmental trigger is not well matched to accretion within the virial volume. We further present FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dark matter halos, two each at the mass of classical dwarf galaxies (Mvir ~ 1010 Msun) and ultra-faint galaxies (Mvir ~ 109 Msun). The resulting central galaxies lie on an extrapolated abundance matching relation from M* ~ 106 to 104 Msun without a break. Our dwarfs with M* ~ 106 Msun each have 1-2 well-resolved satellites with M* = 3 - 200 x 103 Msun. Even our isolated ultra-faint galaxies have star-forming subhalos. We combine our results with the ELVIS simulations to show that targeting the ~ 50 kpc regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by ~35% compared to random pointings.The well-resolved ultra-faint galaxies in our simulations (M* ~ 3 - 30 x 103 Msun) form withinMpeak ~ 0.5 - 3 x 109 Msun halos. Each has a uniformly ancient stellar population (> 10 Gyr) owing to reionization-related quenching. More massive systems, in contrast, all have late-time star formation. Our results suggest that Mhalo ~ 5 x 109 Msun is a probable dividing line between halos hosting reionization “fossils” and those hosting dwarfs that can continue to form stars in isolation after reionization.Finally, we perform a systematic Bayesian analysis of rotation vs. dispersion support (vrot/sigma) in 40 dwarf galaxies throughout the Local Volume (LV) over a stellar mass range 103.5 Msun < M* < 108 Msun. We find that the stars in 80% of the LV dwarf galaxies studied – both satellites and isolated systems – are dispersion-supported. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally-supported stellar disks, while gas-poor dwarf spheroidals (dSphs) are kinematically distinct in having dispersion supported stars. We apply the same Bayesian analysis to four of the FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dwarf galaxies (109 Msun < Mvir < 1010 Msun) and show that the simulated isolated dIrr galaxies have stellar ellipticities and stellar vrot/sigma ratios that are consistent with the observed population of dIrrs and dSphs without the need to subject these dwarfs to any external perturbations or…