A Photometrically Detected Forming Cluster of Galaxies at Redshift 1.6 in the GOODS Field

TL;DR

This paper reports the photometric discovery of a forming galaxy cluster at redshift 1.6 in the GOODS field, analyzing its properties, galaxy populations, and mass estimates, indicating an early stage of cluster formation.

Contribution

First photometric detection and characterization of a forming galaxy cluster at z=1.6 using the GOODS-MUSIC catalog and (2+1)D density estimation technique.

Findings

Identified a significant galaxy overdensity at z~1.6.

Member galaxies differ from field galaxies, supporting the structure's reality.

Estimated cluster mass range is 1.3x10^14 to 5.7x10^14 Msun.

Abstract

We report the discovery of a localized overdensity at z~1.6 in the GOODS-South Field, presumably a poor cluster in the process of formation. The three-dimensional galaxy density has been estimated on the basis of well calibrated photometric redshifts from the multiband photometric GOODS-MUSIC catalog using the (2+1)D technique. The density peak is embedded in the larger scale overdensity of galaxies known to exist at z=1.61 in the area. The properties of the member galaxies are compared to those of the surrounding field and we found that the two populations are significantly different supporting the reality of the structure. The reddest galaxies, once evolved according to their best fit models, have colors consistent with the red sequence of lower redshift clusters. The estimated M_200 total mass of the cluster is in the range 1.3 x 10^14 - 5.7x 10^14 Msun, depending on the assumed bias factor b. An upper limit for the 2-10 keV X-ray luminosity, based on the 1Ms Chandra observations, is L_X=0.5 x 10^43 erg s^-1, suggesting that the cluster has not yet reached the virial equilibrium.