arXiv:The dark matter content of a gravitationally bound halo | Astronomical Informant

arXiv:The dark matter content of a gravitationally bound halo is known to be affected by the galaxy and gas it hosts. We characterise this response for haloes spanning over four orders of magnitude in mass in the hydrodynamical simulation suites IllustrisTNG and EAGLE using their default astrophysical models and respective gravity-only counterparts. We present simple fitting functions in the quasi-adiabatic relaxation framework that accurately capture the dark matter response over the full range of halo mass and halo-centric distance we explore. We also study the dependence of this response on several halo and galaxy properties beyond total mass. We show that commonly employed schemes, which consider the relative change in radius $r_f/r_i-1$ of a spherical dark matter shell to be a function of only the relative change in its mass $M_i/M_f-1$, do not accurately describe the measured response of most haloes in IllustrisTNG and EAGLE. Rather, $r_f/r_i$ additionally explicitly depends upon halo-centric distance $r_f/R_{\rm vir}$ for haloes with virial radius $R_{\rm vir}$, being very similar between IllustrisTNG and EAGLE. We also identify a previously unmodelled effect, likely driven by feedback-related outflows, in which shells having $r_f/r_i\simeq1$ (i.e., no relaxation) have $M_i/M_f$ significantly different from unity. Our results are immediately applicable to a number of semi-analytical tools for modelling galactic and large-scale structure (baryonification schemes, rotation curves, total mass profiles, etc.). We discuss how these results can be extended to build a deeper physical understanding of the connection between dark matter and baryons at small scales.

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