GREEN PEA GALAXIES AND COHORTS: LUMINOUS COMPACT EMISSION-LINE GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

We present a large sample of 803 star-forming luminous compact galaxies (LCGs) in the redshift range z = 0.02-0.63, selected from Data Release 7 of the Sloan Digital Sky Survey (SDSS). The global properties of these galaxies are similar to those of the so-called green pea star-forming galaxies in the redshift range z = 0.112-0.360 and selected from the SDSS on the basis of their green color and compact structure. In contrast to green pea galaxies, our LCGs are selected on the basis of both their spectroscopic and photometric properties, resulting in a ∼10 times larger sample, with galaxies spanning a redshift range ∼>2 times larger. We find that the oxygen abundances and the heavy element abundance ratios in LCGs do not differ from those of nearby low-metallicity blue compact dwarf galaxies. The median stellar mass of LCGs is ∼109 Msun. However, for galaxies with high EW(Hβ), ≥ 100 A, it is only ∼7 x 108 Msun. The star formation rate in LCGs varies in the large range of 0.7-60 Msun yr-1, with a median value of ∼4 Msun yr-1, a factor of ∼3 lower than in high-redshift star-forming galaxies at z ∼> 3. The specific star formation rates in LCGs are extremely high and vary in the range ∼10-9-10-7 yr-1, comparable to those derived in high-redshift galaxies.