Why Baryons Matter: The Kinematics of Dwarf Spheroidal Satellites (1207.2468v3)

Abstract: We use high resolution cosmological simulations of Milky Way-mass galaxies that include both baryons and dark matter to show that baryonic physics (energetic feedback from supernovae and subsequent tidal stripping) significantly reduces the dark matter mass in the central regions of luminous satellite galaxies. The reduced central masses of the simulated satellites reproduce the observed internal dynamics of Milky Way and M31 satellites as a function of luminosity. We use these realistic satellites to update predictions for the observed velocity and luminosity functions of satellites around Milky Way-mass galaxies when baryonic effects are accounted for. We also predict that field dwarf galaxies in the same luminosity range as the Milky Way classical satellites should not exhibit velocities as low as the satellites, since the field dwarfs do not experience tidal stripping. Additionally, the early formation times of the satellites compared to field galaxies at the same luminosity may be apparent in the star formation histories of the two populations. Including baryonic physics in Cold Dark Matter models naturally explains the observed low dark matter densities in the Milky Way's dwarf spheroidal population. Our simulations therefore resolve the tension between kinematics predicted in Cold Dark Matter theory and observations of satellites, without invoking alternative forms of dark matter.

• The paper demonstrates that including baryonic physics causes core formation and reduces central dark matter in satellites via supernova feedback and tidal stripping.
• The methodology employs high-resolution cosmological simulations combining baryons and dark matter, revealing a 50% reduction in surviving subhalos compared to DM-only models.
• Findings resolve the 'too big to fail' issue by aligning satellite radial velocities and luminosities with observations from the Milky Way and Andromeda.

Academic Exploration of the Dynamics of Dwarf Spheroidal Satellites

The paper "Why Baryons Matter: The Kinematics of Dwarf Spheroidal Satellites" by Brooks and Zolotov provides a detailed investigation into the role of baryonic physics in the dynamics of dwarf spheroidal galaxies orbiting Milky Way-mass galaxies. Through the use of high-resolution cosmological simulations that include both baryons and dark matter (DM), this paper addresses the discrepancy between observed satellite properties and theoretical predictions from the Cold Dark Matter (CDM) model without baryons.

The authors present their findings that baryonic processes, particularly supernovae (SN) feedback and tidal stripping, crucially affect the dark matter content in the central regions of luminous satellite galaxies. Their simulations show that SN feedback can lead to the formation of cores in the DM distributions of these satellites, subsequently leading to enhanced mass loss via tidal stripping when these satellites orbit a massive baryonic disk. This combination results in a significant reduction in the central dark matter densities of the satellites.

Key numerical results from the simulations demonstrate that the inclusion of baryonic physics results in satellites with radial velocities and luminosities consistent with observational data of the Milky Way and Andromeda (M31) dwarfs. The paper potently argues against the necessity of alternate dark matter forms, such as warm or self-interacting DM, as the prevailing CDM model, combined with baryonic processes, satisfactorily reproduces the observed low DM densities in the satellite galaxies.

The paper provides extensive data supporting the claim that there are significant differences in the properties of satellite galaxies when baryonic effects are considered. A notable assertion made by the paper is that for any given mass or maximum circular velocity, the number of surviving subhalos in simulations including baryons is reduced by approximately 50% compared to DM-only simulations. Furthermore, the paper finds robust evidence that baryonic interactions significantly influence the kinematic diversity observed in satellite galaxies, erasing strict correlations between luminosity and central mass that exist at infall time.

This research has several implications. Theoretically, it counters the "too big to fail" problem by suggesting that the simulations incorporating baryonic physics need not invoke modified DM models to match observations. Practically, the results underline the necessity of including baryonic processes in simulations aiming to make accurate predictions about satellite galaxy dynamics.

Future developments in astrophysical research, particularly in simulating galaxies, should consider the role of baryons in fine-tuning the predictions of satellite galaxy properties. Additionally, comparisons with various DM models, including baryons, could provide further insights into the balance of forces shaping galaxies. Understanding the interplay of baryonic physics and dark matter will continue to be a pivotal aspect of understanding cosmic structures and the evolution of galaxies.