Accretion history dependence of the halo depletion radius

Abstract

We investigate the role of the accretion history in shaping the depletion radius of dark matter halos using a large cosmological N-body simulation. We show that the inner depletion radius, rescaled by the virial radius, depends strongly on the recent mass accretion rate (MAR) measured over a dynamical timescale, while exhibiting only weak dependence on halo mass. While this dependence mirrors that of the splashback radius and the two radii are tightly correlated, the depletion radius exhibits a more nuanced response to the detailed accretion mode. Specifically, we find that the dependence on MAR steepens at lower redshifts, aligning with self-similar spherical collapse models yet contrasting with the behavior of the splashback radius. This redshift dependence is largely driven by dynamic events, as it diminishes significantly when halos undergoing recent major mergers are excluded. Furthermore, we identify a dichotomy in the drivers of the depletion radius. For slowly accreting halos, the MAR is the primary dependence, whereas for rapidly accreting halos, other properties (shape, spin, concentration, and formation time of the central subhalo) related to the anisotropic or perturbed accretion mode also play a significant role. These results establish the depletion radius as a sensitive physical probe of the detailed accretion history of dark matter halos, complementary to the splashback radius.

Figures (8)

• Figure 1: Median radial profiles of dark matter halos in different bins of $\Gamma_{\mathrm{dyn}}$. The panels show the density profile (top left), logarithmic density slope (bottom left), radial velocity profile (top right), and mass flow rate (MFR; bottom right), with radial distance scaled by $R_{\mathrm{vir}}$. halos are selected in the mass range $13 \le \log[M_{\mathrm{vir}}/(h^{-1}\mathrm{M}_\odot)] < 13.5$ at $z=0$ and are divided into bins of $\Gamma_{\mathrm{dyn}}$. The corresponding $\Gamma_{\mathrm{dyn}}$ ranges and number of halos in each bin are indicated in the legend. All quantities are normalized by the corresponding virial values.
• Figure 2: Median density slope (top row) and MFR (bottom row) profiles at $z=0$ for halos in different $M_{\mathrm{vir}}$ bins. Each column corresponds to a $\Gamma_{\mathrm{dyn}}$ bin, increasing from left to right. Different line shades denote different halo mass bins, as labeled in the legend. Unfilled and filled circles mark the splashback radius $R_{\mathrm{sp}}$ and the depletion radius $R_{\mathrm{id}}$, respectively, measured from the median profiles.
• Figure 4: Median density slope (top row) and MFR (bottom row) profiles of group-mass dark matter halos at different redshifts. halos are selected at each redshift to have $13 \le \log[M_{\mathrm{vir}}/(h^{-1}\mathrm{M}_\odot)] < 13.5$ and are divided into bins of $\Gamma_{\mathrm{dyn}}$, shown in columns from left to right. Curves of different colors correspond to different redshifts, ranging from $z=3$ (red) to $z=0$ (blue). Radii are scaled by $R_{\mathrm{vir}}$, and physical quantities are normalized by the corresponding virial values at each redshift. $R_{\mathrm{sp}}$ (unfilled circles) and $R_{\mathrm{id}}$ (filled circles) are measured from the median profiles.
• Figure 6: Best-fit parameters $(A, B)$ of the $R_{\mathrm{id}}/R_{\mathrm{vir}}$--$\Gamma_{\mathrm{dyn}}$ relation (Equation \ref{['eq:fitformula']}) as functions of the matter density parameter $\Omega_{\mathrm{m}}$ at each redshift. The orange solid curves show linear fits in $\ln\Omega_{\mathrm{m}}$ to the data points.
• Figure 7: Profiles of slope and MFR for halos excluding recent major mergers, analogous to Figures \ref{['fig:prof_on_m']} and \ref{['fig:prof_on_z']}. The slope profiles remain largely unchanged, whereas the MFR profiles show weaker net infall compared to the full sample, especially for high $\Gamma_{\mathrm{dyn}}$ systems.