Star formation activities in early-type brightest cluster galaxies

TL;DR

This study identifies and analyzes star formation activities in early-type Brightest Cluster Galaxies (BCGs) using SDSS data, revealing their recent minor starbursts, correlation with cluster richness, and differences between optically-selected and X-ray luminous clusters.

Contribution

It provides the first comprehensive analysis of star formation in early-type BCGs, highlighting the impact of cluster environment and cooling flows on star formation activity.

Findings

Star-forming BCGs constitute about 0.5% of the sample.

Recent star formation contributes less than 1% of stellar mass.

Higher SFRs are observed in BCGs within richer clusters.

Abstract

We identify a total of 120 early-type Brightest Cluster Galaxies (BCGs) at 0.1<z<0.4 in two recent large cluster catalogues selected from the Sloan Digital Sky Survey (SDSS). They are selected with strong emission lines in their optical spectra, with both H{\alpha} and [O II]{\lambda}3727 line emission, which indicates significant ongoing star formation. They constitute about ~ 0.5% of the largest, optically-selected, low-redshift BCG sample, and the fraction is a strong function of cluster richness. Their star formation history can be well described by a recent minor and short starburst superimposed on an old stellar component, with the recent episode of star formation contributing on average only less than 1 percent of the total stellar mass. We show that the more massive star-forming BCGs in richer clusters tend to have higher star formation rate (SFR) and specific SFR (SFR per unit galaxy stellar mass). We also compare their statistical properties with a control sample selected from X-ray luminous clusters, and show that the fraction of star-forming BCGs in X-ray luminous clusters is almost one order of magnitude larger than that in optically-selected clusters. BCGs with star formation in cooling flow clusters usually have very flat optical spectra and show the most active star formation, which may be connected with cooling flows.