Forged in fire: cusps, cores and baryons in low-mass dwarf galaxies

Abstract

We present multiple ultra-high resolution cosmological hydrodynamic simulations of M 10 4−6.3 M dwarf galaxies that form within two M vir = 10 9.5−10 M dark matter halo initial conditions. Our simulations rely on the FIRE implementation of star formation feedback and were run with high enough force and mass resolution to directly resolve structure on the ∼ 200 pc scales. The resultant galaxies sit on the M vs. M vir relation required to match the Local Group stellar mass function via abundance matching. They have bursty star formation histories and also form with half-light radii and metallicities that broadly match those observed for local dwarfs at the same stellar mass. We demonstrate that it is possible to create a large (∼ 1 kpc) constant-density dark matter core in a cosmological simulation of an M 10 6.3 M dwarf galaxy within a typical M vir = 10 10 M halo -precisely the scale of interest for resolving the Too Big to Fail problem. However, these large cores are not ubiquitous and appear to correlate closely with the star formation histories of the dwarfs: dark matter cores are largest in systems that form their stars late (z 2), after the early epoch of cusp building mergers has ended. Our M 10 4 M dwarf retains a cuspy dark matter halo density profile that matches that of a dark-matter only run of the same system. Though ancient, most of the stars in our ultra-faint form after reionization; the UV field acts mainly to suppress fresh gas accretion, not to boil away gas that is already present in the proto-dwarf.

Dark matter annihilation and decay from non-spherical dark halos in galactic dwarf satellites

“…However, Hayashi & Chiba (2012) argued that the mass of the dSphs enclosed within inner 300 pc varies depending on their total luminosities, in contrast to the conclusion of Strigari et al (2008). Furthermore, recent high-resolution simulations (e.g., Di Cintio et al 2014a,b; Oñorbe et al 2015) imply that dark halo structures of classical-and UFD-like galaxies are generally different due to the effects of the stellar feedback energy associated with star formation history. Therefore, we believe that log L, log Vmax and log rmax of dSphs do not necessarily have a linear correlation but rather are independent quantities.…”

Breathing Fire: How Stellar Feedback Drives Radial Migration, Rapid Size Fluctuations, and Population Gradients in Low-Mass Galaxies

“…Recently, a number of studies (for example, Read & Gilmore 2005;Governato et al 2012;Di Cintio et al 2014;Chan et al 2015;Oñorbe et al 2015) have shown that including stellar feedback in simulations can significantly alter dwarf galaxies' density profiles, removing dark matter from the central regions and potentially reconciling the predictions of ΛCDM models with observations, at least for galaxies with M star =10 7−9.6 M e (M halo ≈10 10−11.5 M e ). We find similar dynamics for the stellar population, which is not surprising given that both stars and dark matter behave as Figure 9.…”

The VIMOS Ultra Deep Survey

“…At low redshifts the feedback effects have been proposed as the ones that have the major impact on the evolution of dwarf galaxies (see, e.g., Ferrara & Tolstoy 2000;Fujita et al 2004;Mashchenko et al 2008;Sawala et al 2011;Kawata et al 2014;Oñorbe et al 2015;Chen et al 2016;Papastergis & Shankar 2016). Our SHMR measurements, i.e., the higher than expected star formation efficiency, suggest that at z ∼ 3 a positive feedback effects have a significant influence on stellar mass assembly in not only dwarf galaxies (M < 10 9 ), like it is observed locally, but also in more massive ones, which at z = 0 are not observed to be strongly affected.…”