Baryons Matter: Why Luminous Satellite Galaxies Have Reduced Central Masses (1207.0007v3)

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 (Mvir > 10^9 Msun, Mstar > 10^7 Msun) 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, tidal stripping acts to further reduce the central densities of the luminous satellites, particularly those that enter with cored dark matter halos, increasing the discrepancy in the central masses predicted by baryon+DM and DM-only simulations. We show that DM-only simulations, which neglect the baryonic effects 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.

• The paper demonstrates that high-resolution simulations reveal supernova feedback and tidal stripping effectively lower central dark matter densities in luminous satellites.
• It employs detailed hydrodynamical models incorporating H2 formation to accurately trace star formation in Milky Way-mass disk galaxies.
• The findings challenge dark matter–only simulations, urging corrections to better predict the structural properties of satellite galaxies.

Analyzing Reduced Central Masses in Luminous Satellite Galaxies

The research by Adi Zolotov et al., titled "Baryons Matter: Why Luminous Satellite Galaxies Have Reduced Central Masses," investigates the structural dynamics of satellite galaxies influenced by baryonic physics. Utilizing high-resolution cosmological hydrodynamical simulations, the paper elucidates the effects of supernova feedback and tidal stripping on the central masses of satellite galaxies, challenging the conventional expectations established by dark matter-only (DM-only) simulations.

The simulations focus on Milky Way-mass disk galaxies and resolve high-density regions that foster star formation, thereby enabling the authors to deploy a prescription for H$_2$ formation and destruction. This capability anchors the star formation processes to the presence of molecular gas, which is shielded. As a result, in satellite progenitors with notable masses, supernova feedback is effective in reducing dark matter densities and flattening inner density profiles. These findings are in stark contrast with the outcomes of DM-only simulations, which produce steeper inner density profiles.

The analysis discerns a bifurcation in effects based on satellite mass. For massive satellite progenitors (M$_{vir} \ge 10^9 M_{\odot}$, M$_{\star} \ge 10^7 M_{\odot}$), bursts of clumpy star formation drive the formation of shallower dark matter cores, a phenomenon not apparent in low-mass progenitors, which succumb to early gas loss and suppressed star formation post-reionization. After infall, baryonic processes such as gas stripping and tidal effects further act to decrease the central dark matter density in satellites, emphasizing the substantial discrepancy between simulations incorporating baryons and those neglecting them.

The implications of these findings are significant, particularly in the domain of interpreting kinematic observations of dwarf satellites. The results caution against uncritically applying DM-only simulations to real-world scenarios, as they fail to capture the nuanced baryonic influences that lower the central masses predicted for Milky Way's satellite galaxies. As a remedy, the paper suggests a correction method for DM-only simulations, thereby potentially realigning theoretical models with observational data.

In the broader theoretical landscape, the paper resonates with ongoing debates within the cold dark matter (CDM) paradigm, addressing both the "missing satellite problem" and the "core/cusp problem." The baryonic processes highlighted here provide a possible reconciliation avenue, reducing the predicted satellite counts without invoking non-standard cosmologies like warm or self-interacting dark matter.

Looking forward, the research accentuates the need for continued exploration of baryonic physics in galaxy formation models. Future developments in simulation techniques and computational capacities could refine these insights further, potentially furnishing a unified understanding of both galaxy formation and the associated satellite dynamics in the CDM framework. Such advancements would be instrumental in bolstering our theoretical comprehension of galaxy evolution on not only small but also on large cosmic scales.