Clustering of red galaxies around the z=1.53 quasar 3C270.1

TL;DR

This study identifies a potential galaxy cluster around the z=1.53 quasar 3C270.1 by detecting an excess of red galaxies with properties suggesting both passive ellipticals and dusty starbursts, supporting hierarchical galaxy formation models.

Contribution

It provides observational evidence of a proto-cluster around a high-redshift quasar using multi-wavelength photometry and SED analysis, highlighting the diversity of galaxy types in early cluster formation.

Findings

Excess of 11 extremely red objects near the quasar.

Most EROs are consistent with passive elliptical galaxies.

One ERO shows signs of dust-enshrouded starburst activity.

Abstract

In the paradigm of hierarchical galaxy formation, luminous radio galaxies mark mass assembly peaks that should contain clusters of galaxies. Observations of the z=1.53 quasar 3C270.1 with the Spitzer Space Telescope at 3.6-24 micron and with the 6.5-m MMT in the z'- and Y-bands allow detection of potential cluster members via photometric redshifts. Compared with nearby control fields, there is an excess of 11 extremely red objects (EROs) at 1.33 < z_phot < 1.73, consistent with a proto-cluster around the quasar. The spectral energy distributions (SEDs) of 3/4 of the EROs are better fitted with passive elliptical galaxies than withdust-reddened starbursts, and of four sources well-detected on an archival HST snapshot image, all have undisturbed morphologies. However, one ERO, not covered by the HST image, is a double source with 0.8" separation on the z' image and a marginal (2sigma) 24 micron detection indicating a dust-enshrouded starburst. The EROs are more luminous than L* (H = -23.6 AB mag at z=1.5).