The no-spin zone: rotation vs dispersion support in observed and simulated dwarf galaxies

Coral Wheeler; Andrew B. Pace; James S. Bullock; Michael Boylan-Kolchin; Jose Onorbe; Oliver D. Elbert; Alex Fitts; Philip F. Hopkins; Dusan Keres

doi:10.1093/mnras/stw2583

paper

The no-spin zone: rotation vs dispersion support in observed and simulated dwarf galaxies

arXiv:1511.01095 · doi:10.1093/mnras/stw2583

Abstract

We perform a systematic Bayesian analysis of rotation vs. dispersion support ( $v_{rot} / σ$ ) in $40$ dwarf galaxies throughout the Local Volume (LV) over a stellar mass range $1 0^{3.5} M_{⊙} < M_{⋆} < 1 0^{8} M_{⊙}$ . We find that the stars in $\sim 80%$ of the LV dwarf galaxies studied -- both satellites and isolated systems -- are dispersion-supported. In particular, we show that $6/10$ *isolated* dwarfs in our sample have $v_{rot} / σ < 1.0$ . All have $v_{rot} / σ ≲ 2.0$ . 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 see no clear trend between $v_{rot} / σ$ and distance to the closest $L_{⋆}$ galaxy, nor between $v_{rot} / σ$ and $M_{⋆}$ within our mass range. We apply the same Bayesian analysis to four FIRE hydrodynamic zoom-in simulations of isolated dwarf galaxies ( $1 0^{9} M_{⊙} < M_{vir} < 1 0^{10} M_{⊙}$ ) and show that the simulated *isolated* dIrr galaxies have stellar ellipticities and stellar $v_{rot} / σ$ ratios that are consistent with the observed population of dIrrs *and* dSphs without the need to subject these dwarfs to any external perturbations or tidal forces. We posit that most dwarf galaxies form as puffy, dispersion-dominated systems, rather than cold, angular momentum-supported disks. If this is the case, then transforming a dIrr into a dSph may require little more than removing its gas.

13 pages, 1 table, 4 figures. Accepted in MNRAS

The no-spin zone: rotation vs dispersion support in observed and simulated dwarf galaxies

Abstract

References in corpus (49)

Cited by in corpus (82)