Stellar Mass and 3.4 $\mu$m M/L Ratio Evolution of Brightest Cluster Galaxies in COSMOS since z ~ 1.0

TL;DR

This study examines the evolution of stellar mass, star formation rates, and mass-to-light ratios of brightest cluster galaxies since redshift 1, revealing lower star formation activity compared to more massive clusters and passive stellar aging.

Contribution

It provides new insights into the evolution of BCG properties over time and compares star formation activity across different cluster samples, highlighting potential biases.

Findings

Star formation in COSMOS BCGs is similar to that in more massive clusters but is lower by ~1 dex.

The M/L ratio evolution aligns with passive stellar aging.

A correlation between 3.4 μm luminosity and stellar mass is established up to z ~ 1.

Abstract

We investigate the evolution of star formation rates (SFRs), stellar masses, and M/L$_{3.4 \mu m}$ ratios of brightest cluster galaxies (BCGs) in the COSMOS survey since z ~ 1 to determine the contribution of star formation to the growth-rate of BCG stellar mass over time. Through the spectral energy distribution (SED) fitting of the GALEX, CFHT, Subaru, Vista, Spitzer, and Herschel photometric data available in the COSMOS2015 catalog, we estimate the stellar mass and SFR of each BCG. We use a modified version of the iSEDfit package to fit the SEDs of our sample with both stellar and dust emission models, as well as constrain the impact of star formation history assumptions on our results. We find that in our sample of COSMOS BCGs, star formation evolves similarly to that in BCGs in samples of more massive galaxy clusters. However, compared to the latter, the magnitude of star formation in our sample is lower by ~ 1 dex. Additionally, we find an evolution of BCG baryonic mass-to-light ratio (M/L$_{3.4 \mu m}$) with redshift which is consistent with a passively aging stellar population. We use this to build upon Wen et al.'s (2013) low-redshift $\nu$L$_{3.4 \mu m}$-M$_{Stellar}$ relation, quantifying a correlation between $\nu$L$_{3.4 \mu m}$ and M$_{Stellar}$ to z ~ 1. By comparing our results to BCGs in Sunyaev-Zel'dovich and X-ray-selected samples of galaxy clusters, we find evidence that the normalization of star formation evolution in a cluster sample is driven by the mass range of the sample and may be biased upwards by cool cores.