Ongoing growth of the brightest cluster galaxies via major dry mergers in the last ~6 Gyr

Abstract

Brightest Cluster Galaxies (BCGs) might have been assembled relatively late (z<1) via mergers. By exploiting the high-resolution HST/ACS imaging, we find four BCGs (COSMOS-P 125516, 102810, 036694 and 089357) in major dry merging in 29 X-ray clusters at $0.3\le z\le 0.6$ in the Cosmological Evolutionary Survey (COSMOS). These BCGs show prominent but quiescent double nuclei with a magnitude difference of $\delta m<1.5$ and a projected separation of $r_p<$ 10 kpc. Clear signatures of interaction such as extended plumes and/or significant asymmetries are also observed in their residual images. We infer a major merger rate of $0.55\pm 0.27$ merger per Gyr at $z\sim 0.43$ assuming the merger time-scale estimate of Kitzbichler & White (2008). This inferred rate is significantly higher than the rate in the local Universe ($0.12\pm 0.03$ at $z\sim 0.07$) presented in Liu et al. (2009). We estimate that present-day BCGs increase their luminosity (mass) by $\sim 35\pm 15$ per cent $(f_{mass}/0.5)$ via major dry mergers since $z=0.6$, where $f_{mass}$ is the mean mass fraction of companion galaxies accreted onto the central ones. Although the statistical uncertainty due to our small sample size is relatively large, our finding is consistent with both recent observational and theoretical results. Furthermore, in conjunction with our previous findings in Liu et al. (2009), the discovery of these intermediate-redshift merging BCGs is clear evidence of ongoing assembly of BCGs via major dry mergers over the last $\sim$6 Gyr.

8 pages, 4 figures and 1 table, accepted for publication in MNRAS

References in corpus (15)

• The hierarchical formation of the brightest cluster galaxies
• COSMOS Photometric Redshifts with 30-bands for 2-deg2
• Photometric redshift and classification for the XMM-COSMOS sources
• How special are Brightest Group and Cluster Galaxies?
• The XMM-Newton wide-field survey in the COSMOS field: VI. Statistical properties of clusters of galaxies
• The luminosities, sizes and velocity dispersions of Brightest Cluster Galaxies: Implications for formation history
• A calibration of the relation between the abundance of close galaxy pairs and the rate of galaxy mergers
• Ongoing Assembly of Massive Galaxies by Major Merging in Large Groups and Clusters from the SDSS
• Photometric Redshifts of Galaxies in COSMOS
• Photometric Properties and Scaling Relations of Early Type Brightest Cluster Galaxies
• X-ray Selected Intermediate-Redshift Groups of Galaxies
• The Late Stellar Assembly of Massive Cluster Galaxies Via Major Merging
• An imaging survey of a uniform sample of Brightest Cluster Galaxies and Intracluster Light
• An Extremely Massive Dry Galaxy Merger in a Moderate Redshift Cluster
• On the Formation of cD Galaxies and their Parent Clusters

Cited by in corpus (2)

• Hot Jupiters from Coplanar High-eccentricity Migration
• The XXL survey XV: Evidence for dry merger driven BCG growth in XXL-100-GC X-ray clusters