The different growth pathways of Brightest Cluster Galaxies and the Intra-Cluster Light

Abstract

We study the growth pathways of Brightest Central Galaxies (BCGs) and Intra-Cluster Light (ICL) by means of a semi-analytic model. We assume that the ICL forms by stellar stripping of satellite galaxies and violent processes during mergers, and implement two independent models: (1) one considers both mergers and stellar stripping (named STANDARD model), and one considers only mergers (named MERG-ERS model). We find that BCGs and ICL form, grow and overall evolve at different times and with different timescales, but they show a clear co-evolution after redshift z ∼ 0.7 − 0.8. Around 90% of the ICL from stellar stripping is built-up in the innermost 150 Kpc from the halo centre and the dominant contribution comes from disk-like galaxies (B/T<0.4) through a large number of small/intermediate stripping events (M strip /M sat < 0.3). The fractions of stellar mass in BCGs and in ICL over the total stellar mass within the virial radius of the halo evolve differently with time. At high redshift, the BCG accounts for the bulk of the mass, but its contribution gradually decreases with time and stays constant after z ∼ 0.4 − 0.5. The ICL, instead, grows very fast and its contribution keeps increasing down to the present time. The STANDARD and the MERGERS models make very similar predictions in most of the cases, but predict different amounts of ICL associated to other galaxies within the virial radius of the group/cluster other than the BCG, at z = 0. We then suggest that this quantity is a valid observable that can shed light on the relative importance of mergers and stellar stripping for the formation of the ICL.

The Rest-frame H-band Luminosity Function of Red-sequence Galaxies in Clusters at 1.0 < z < 1.3

“…Hence, the growth of the BCGs would correspond to ∼3% (∼1%) of the total red-sequence luminosity, assuming they grow uniformly in time. Similarly, the contribution of the growth of the ICL to the red-sequence luminosity is also not significant; simulations show that most of the ICL assembles after z∼1 and its fraction of mass grows from ∼5%−10% to ∼30%−40% of its z∼0 value between z∼1.15 and z∼0.60 (Contini et al 2014(Contini et al , 2018. They show that the stellar mass growth of the ICL has a BCG mass dependence.…”

“…We are aware that the total magnitude is not an accurate measurement of the stellar component of the BCG. Strictly speaking, the total magnitude measures BCG+ICL as we did not separate the ICL from the outer halo of the BCG, although it is known that the BCG accounts for the bulk of the BCG+ICL mass at z∼1(Contini et al 2018). Here, we simply use the luminosity of the BCGs to show that the effect of BCG growth on the red-sequence luminosity is negligible.…”

The growth of brightest cluster galaxies and intracluster light over the past 10 billion years

“…However, semianalytic models and numerical simulations typically predict substantial late-time growth of the ICL. For example, the semi-analytic models of Contini et al (2014Contini et al ( , 2018, which are based upon the Millennium simulations, predict that the ICL has doubled in stellar mass since z = 0.5. Several recent observational studies concur, suggesting that this growth is driven by the addition of stars from mergers and stripping events (Burke et al 2012;Zhang et al 2016).…”

On the Origin and Evolution of the Intra-Cluster Light: A Brief Review of the Most Recent Developments

“…For a historical survey, I refer the reader to, e.g., the review by Montes M. [2]). Most of the ICL in clusters is considered to be somehow associated with the brightest cluster galaxy (hereafter BCG), which is the galaxy that resides in the center of clusters (for the sake of simplicity, I will call BCGs also those residing in the center of galaxy groups), while a smaller fraction of the total is found, and also predicted, to be around intermediate and massive satellites (e.g., [3][4][5][6]). The BCG and its associated ICL are commonly taken as a whole system (e.g., [7][8][9][10][11][12], just to quote a few of the most recent observational studies), given the actual observational difficulty to separate them (I will fully address this point in Section 2).…”