The Transition Region between Brightest Cluster Galaxies and Intracluster Light in Galaxy Groups and Clusters
Emanuele Contini, Hou-Zun Chen, Qiusheng Gu
Abstract
Abstract We take advantage of a state-of-art semianalytic model of galaxy formation, and the model presented by Contini & Gu, to investigate the mass distribution of brightest cluster galaxies (BCGs) and intracluster light (ICL) by addressing two points: (1) the region of transition between a BCG-dominated distribution and an ICL-dominated one, and (2) the relation between the total BCG+ICL mass and the ICL mass alone. We find the transition radius to be independent of both BCG+ICL and halo masses, with an average of 60 ± 40 kpc, in good agreement with previous observational measurements, but given the large scatter it can be considered as a sort of physical separation between the two components only on a cluster scale. From the analysis of the M ICL – M BCG+ICL relation, we construct a method able to extract the ICL mass directly from knowledge of the BCG+ICL mass. Given the large scatter in low-mass systems, such a method under/overpredicts the true value of the ICL in a significant way, up to a factor of three in the worst cases. On the other hand, for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>BCG</mml:mi> <mml:mo>+</mml:mo> <mml:mi>ICL</mml:mi> </mml:mrow> </mml:msub> <mml:mo>></mml:mo> <mml:mn>12</mml:mn> </mml:math> or <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>Halo</mml:mi> </mml:mrow> </mml:msub> <mml:mo>></mml:mo> <mml:mn>14</mml:mn> </mml:math> (where masses are in units of M ⊙ ), the difference between the true value and the one extracted from the M ICL – M BCG+ICL relation ranges between ±30%. We therefore suggest this relation as a reliable test for observational works aiming to isolate the ICL from the BCG, for systems hosted by haloes on a cluster scale.