The Sphere of Influence of the Bright Central Galaxies in the Diffuse Light of SDSS Clusters

TL;DR

This study investigates the transition between bright central galaxies and intracluster light in SDSS clusters, revealing a BCG sphere of influence of about 200 kpc through stacking and component decomposition of stellar mass profiles.

Contribution

It introduces a physically-motivated method to decompose BCG+ICL profiles and identifies a large BCG sphere of influence, linking it to dark matter halo properties.

Findings

The BCG-ICL transition occurs around 200 kpc.

Outer ICL likely originates from satellite stripping.

The BCG sphere of influence extends to approximately 200 kpc.

Abstract

The bright central galaxies (BCGs) dominate the inner portion of the diffuse cluster light, but it is still unclear where the intracluster light (ICL) takes over. To investigate the BCG-ICL transition, we stack the images of ${\sim}3000$ clusters between $0.2{<}z{<}0.3$ in the SDSS $gri$ bands, and measure their BCG+ICL stellar surface mass profile $\Sigma_{*}^{\texttt{B+I}}$ down to $3{\times}10^4\,M_{\odot}/\mathrm{kpc}^{2}$ at $R{\simeq}1\,\mathrm{Mpc}$ (${\sim}32$ mag/arcsec$^2$ in the $r$-band). We develop a physically-motivated method to decompose $\Sigma_{*}^{\texttt{B+I}}$ into three components, including an inner de Vaucouleurs' profile, an outer ICL that follows the dark matter distribution measured from weak lensing, and an intriguing transitional component between 70 and 200 kpc. To investigate the origin of this transition, we split the clusters into two subsamples by their BCG stellar mass $M_*^{\mathrm{BCG}}$ (mass enclosed roughly within 50 kpc) while making sure they have the same distribution of satellite richness. The $\Sigma_{*}^{\texttt{B+I}}$ profiles of the two subsamples differ by more than a factor of two at $R{<}50\,\mathrm{kpc}$, consistent with their 0.34 dex difference in $M_*^{\mathrm{BCG}}$, whereas on scales beyond 400 kpc the two profiles converge to the same amplitudes, suggesting a satellite-stripping origin of the outer ICL. Remarkably, however, the discrepancy between the two $\Sigma_{*}^{\texttt{B+I}}$ profiles persist at above $50\%$ level on all scales below 200 kpc, thereby revealing the BCG sphere of influence with radius $R_{\mathrm{SOI}}{\simeq}$ 200 kpc. Finally, we speculate that the surprisingly large sphere of influence of the BCG is tied to the elevated escape velocity profile within $r_s$, the characteristic radius of the dark matter haloes.