Spectroscopy of Luminous Compact Blue Galaxies in Distant Clusters I. Spectroscopic Data

TL;DR

This study used spectroscopic data from the Keck II Telescope to identify and analyze luminous, compact, blue galaxies in distant galaxy clusters, revealing their high density and environmental dependence at redshifts 0.5 to 0.9.

Contribution

First spectroscopic confirmation of LCBGs in distant clusters, showing their significant density enhancement and environmental triggering at intermediate redshifts.

Findings

LCBGs are highly concentrated in galaxy clusters at z=0.5-0.9.

The density of LCBGs exceeds field density by over 400 times.

LCBGs are preferentially triggered in high-density environments.

Abstract

We used the DEIMOS spectrograph on the Keck II Telescope to obtain spectra of galaxies in the fields of five distant, rich galaxy clusters over the redshift range 0.5 < z < 0.9 in a search for luminous, compact, blue galaxies (LCBGs). Unlike traditional studies of galaxy clusters, we preferentially targeted blue cluster members identified via multi-band photometric pre-selection based on imaging data from the WIYN telescope. Of the 1288 sources that we targeted, we determined secure spectroscopic redshifts for 848 sources, yielding a total success rate of 66%. Our redshift measurements are in good agreement with those previously reported in the literature, except for 11 targets which we believe were previously in error. Within our sample, we confirm the presence of 53 LCBGs in the five galaxy clusters. The clusters all stand out as distinct peaks in the redshift distribution of LCBGs with the average number density of LCBGs ranging from 1.65+-0.25 Mpc^-3 at z=0.55 to 3.13+-0.65 Mpc^-3 at z=0.8. The number density of LCBGs in clustes exceeds the field desnity by a factor of 749+-116 at z=0.55; at z=0.8, the corresponding ratio is E=416+-95. At z=0.55, this enhancement is well above that seen for blue galaxies or the overall cluster population, indicating that LCBGs are preferentially triggered in high-density environments at intermediate redshifts.