Three-Dimensional Hydrodynamical Simulations of the Supernovae-Driven Gas Loss in the Dwarf Spheroidal Galaxy Ursa Minor

Abstract

As is usual in dwarf spheroidal galaxies, today the Local Group galaxy Ursa Minor is depleted of its gas content. How this galaxy lost its gas is still a matter of debate. To study the history of gas loss in Ursa Minor, we conducted the first three-dimensional hydrodynamical simulations of this object, assuming that the gas loss was driven by galactic winds powered only by type II supernovae (SNe II). The initial gas setup and supernova (SN) rates used in our simulations are mainly constrained by the inferred star formation history and the observed velocity dispersion of Ursa Minor. After 3 Gyr of evolution, we found that the gas removal efficiency is higher when the SN rate is increased, and also when the initial mean gas density is lowered. The derived mass-loss rates are systematically higher in the central regions (< 300 pc), even though such a relationship has not been strictly linear in time and in terms of the galactic radius. The filamentary structures induced by Rayleigh-Taylor instabilities and the concentric shells related to the acoustic waves driven by SNe can account for the inferred mass losses from the simulations. Our results suggest that SNe II are able to transfer most of the gas from the central region outward to the galactic halo. However, other physical mechanisms must be considered in order to completely remove the gas at larger radii.

High-resolution three-dimensional simulations of gas removal from ultrafaint dwarf galaxies

“…Our results strengthen previous findings in the literature (e.g. Marcolini et al 2006;Caproni et al 2015) that such a criterion could be too simplistic, and that perhaps the role of stellar feedback in the regulation of star formation in dwarf galaxies needs to be reconsidered. In the past, it has been also pointed out that the compression due to a large accumulation of energy from nearby OB associations might lead to very high gas densities, with very rapid cooling and dissipation of such energy and, consequently, inefficient effects of feedback (e.g.…”

Gas Removal in the Ursa Minor Galaxy: Linking Hydrodynamics and Chemical Evolution Models

“…As in Caproni et al (2015), the Cartesian grid of the computational domain is assumed to be invariant in time, which means the effects of cosmological expansion in our simulations were neglected. We simulated a cubic region of 3 kpc × 3 kpc × 3 kpc (∼ 1.6R t , the tidal radius of Ursa Minor; Irwin & Hatzidimitriou 1995), in which a grid with 256 points in each Cartesian direction was adopted.…”

“…where n is the number density of the gas and Λ(T ), obtained from the interpolation of the precomputed tables provided by Wiersma, Schaye & Smith (2009). To compute the values of Λ(T ), we follow Caproni et al (2015), adopting [Fe/H] ∼ −2.13, the median metallicity of Ursa Minor (Kirby et al 2011). We used in our simulation the same initial gas density and pressure profiles of the models Mgh19SN1 and Mgh19SN10 found in Caproni et al (2015).…”

“…To compute the values of Λ(T ), we follow Caproni et al (2015), adopting [Fe/H] ∼ −2.13, the median metallicity of Ursa Minor (Kirby et al 2011). We used in our simulation the same initial gas density and pressure profiles of the models Mgh19SN1 and Mgh19SN10 found in Caproni et al (2015). They were fully determined imposing hydrostatic equilibrium between an initial, isothermal gas with sound speed, c s0 , of 11.5 km −1 , and a cored, static dark-matter (DM) gravitational potential, Φ h (Binney & Tremaine 1987;Mac Low & Ferrara 1999):…”

“…We show in Figure 1 the initial spatial distribution of the number density, temperature, and radial velocity, v rad , on xy plane at z = 0. The last quantity is defined as (Caproni et al 2015): Figure 2. Supernova rates adopted in our hydrodynamical simulation of the gas in dSph galaxy Ursa Minor.…”