Spectroscopic confirmation of a galaxy cluster associated with 7C?1756+6520 at z = 1.416

摘要

We present spectroscopic follow-up of an overdensity of galaxies photometrically selected to be at 1.4 < z < 2.5 found in the vicinity of the radio galaxy 7C1756+6520 at z =1.4156. Using the DEIMOS optical multi-object spectrograph on the Keck 2 telescope, we observed a total of 129 BzK-selected sources, comprising 82 blue, star-forming galaxy candidates (sBzK) and 47 red, passively-evolving galaxy candidates (pBzK*),as well as 11 mid-infrared selected AGN candidates. We obtain robustspectroscopic redshifts for 36 blue galaxies, 7 red galaxies and 9 AGNcandidates. Assuming all foreground interlopers were identified, wefind that only 16% (9%) of the sBzK (pBzK*) galaxies are at z<1.4. Therefore, the BzKcriteria are shown to be relatively robust at identifying galaxies atmoderate redshifts. Twenty-one galaxies, including the radio galaxy,four additional AGN candidates and three red galaxy candidates arefound with ,forming a large scale structure at the redshift of the radio galaxy. Ofthese, eight have projected offsets <2Mpc relative to theradio galaxy position and havevelocity offsets <1000kms-1 relative to theradio galaxy redshift. This confirms that 7C1756+6520 isassociated with a high-redshift galaxy cluster. A second compact groupoffour galaxies is found at ,forming a sub-group offset by kms-1 and approximately east of the radio galaxy. Key words: large-scale structure of Universe - galaxies:clusters: general - Galaxy: evolution - galaxies: individual:7C1756+6520- galaxies: clusters: individual: 7C1756+6520