Baryons Matter: Why Luminous Satellite Galaxies Have Reduced Central Masses

Abstract

Using high resolution cosmological hydrodynamical simulations of Milky Way-massed disk galaxies, we demonstrate that supernovae feedback and tidal stripping lower the central masses of bright (−15 < M V < −8) satellite galaxies. These simulations resolve high density regions, comparable to giant molecular clouds, where stars form. This resolution allows us to adopt a prescription for H 2 formation and destruction that ties star formation to the presence of shielded, molecular gas. Before infall, supernova feedback from the clumpy, bursty star formation captured by this physically motivated model leads to reduced dark matter (DM) densities and shallower inner density profiles in the massive satellite progenitors (M vir ≥ 10 9 M ⊙ , M * ≥ 10 7 M ⊙ ) compared to DM-only simulations. The progenitors of the lower mass satellites are unable to maintain bursty star formation histories, due to both heating at reionization and gas loss from initial star forming events, preserving the steep inner density profile predicted by DM-only simulations. After infall, gas stripping from satellites reduces the total central masses of SPH satellites relative to DM-only satellites. Additionally, enhanced tidal stripping after infall due to the baryonic disk acts to further reduce the central DM densities of the luminous satellites. Satellites that enter with cored DM halos are particularly vulnerable to the tidal effects of the disk, exacerbating the discrepancy in the central masses predicted by baryon+DM and DM-only simulations. We show that DM-only simulations, which neglect the highly non-adiabatic evolution of baryons described in this work, produce denser satellites with larger central velocities. We provide a simple correction to the central DM mass predicted for satellites by DM-only simulations. We conclude that DM-only simulations should be used with great caution when interpreting kinematic observations of the Milky Way's dwarf satellites.

Milky Way mass constraints from the Galactic satellite gap

“…Baryonic processes also affect the maximum circular velocity of galactic satellites, especially dwarf spheroidal galaxies (e.g. Zolotov et al 2012;Brooks & Zolotov 2014), which can have important implications for our study. The inclusion of baryons does not affect the maximum circular velocity of massive satellites with V max ∼ 60 km s −1 , but it does lead to an average ∼10 per cent reduction in the maximum circular velocity of satellites with V max 30 km s −1 (Sawala et al in preparation, private communication).…”

In-N-Out: The Gas Cycle From Dwarfs to Spiral Galaxies

“…d Appears in Christensen et al (2012). e Appears in Zolotov et al (2012). Raiteri et al (1996) and distributed across the smoothing sphere.…”

The masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data

“…Comparisons of the satellite populations of observed galaxies (or groups) provide valuable insights as to the relevant physical processes that dominate galaxy formation, as highlighted by the well-known 'missing satellites' (Klypin et al 1999; Moore et al 1999) and 'too big to fail' (Boylan-Kolchin, Bullock & Kaplinghat 2011) problems, which suggest either that our Universe is not well described by a CDM cosmology, or that using numerical simulations to predict observations is more complicated than anticipated. While the former may in fact be true, the latter is now well established, as the formation of galaxies inside dark matter haloes depends strongly on baryonic physics not included in N-body simulations, and the influence of baryons tends to alleviate these problems (Zolotov et al 2012).…”