Galaxy Clusters around z~1-2 Low Luminosity Radio Galaxies

2018-05-29T12:06:47Z (GMT) by Gianluca Castignani

At variance with powerful radio galaxies Low Luminosity Radio Galaxies (LLRGs) are almost invariably found in clusters and often associated with the brightest cluster galaxies, at least at low-redshifts.  In order to prove that this holds also at high-z we exploit a sample of 32 LLRGs at z~1-2 drawn from the COSMOS survey and search for Mpc-scale overdensities using photometric redshifts and our recently developed Poisson Probability Method. We find that ~70% of the LLRGs reside in rich groups or clusters. This fraction is higher than that found for powerful radio galaxies at similar redshifts and is in excellent agreement with results obtained at low redshifts. Independent confirmation of some of our cluster candidates is found in catalogs of clusters selected in  X-rays or spectroscopically. Our strategy is unbiased with respect to colors and star formation history of cluster galaxies and represents a valuable alternative to conventional methods that search for clusters. We observed with the 30 mt. IRAM telescope two of our z=1 LLRGs in clusters to search for molecular gas and set CO upper limits. Our clusters are optimal targets for mm-obsevations with NOEMA and ALMA.