Caltech Faint Galaxy Redshift Survey. VIII. Analysis of the Field J0053+1234

Abstract

The results of a spectroscopic investigation of a complete sample of objects with K_s<20 mag in a 2' by 7.'3 field at J005325+1234 are reported. Redshifts were successfully obtained for 163 of the 195 objects in the sample; these redshifts lie in the range [0.173, 1.44] and have a median of 0.58 (excluding 24 Galactic stars). The redshift identifications are believed to be almost complete for z<0.8. Approximately one-half of the galaxies lie in five narrow redshift features with local velocity dispersions of ~300 km s^(-1). These narrow redshift "peaks" are primarily populated both by absorption-line galaxies and the most luminous galaxies in the sample, although the incidence of emission lines in the luminous galaxies increases with redshift. The estimated dynamical masses of these redshift peaks, and the sky distribution of the galaxies within them, appear similar to groups or poor clusters of galaxies in the local universe at various stages of virialization. Some groups of galaxies therefore form at epochs z>1.5, and the galaxies in such groups appear to be coeval and to show little sign of ongoing star formation. The galaxies outside the redshift peaks are also clustered, albeit more weakly, are less luminous and more frequently exhibit strong emission lines. These "isolated" galaxies therefore appear, on average, to form stars at later epochs than the strongly clustered galaxies. The galaxy spectral energy distributions (SEDs) derived from our UBVRIK photometry are also very closely correlated with the galaxy spectral types and luminosities. These results have strong implications for the analysis of redshift surveys at intermediate redshift. The sample is used to investigate the evolution of the combined galaxy luminosity function back to z=0.8. No significant change is found in the characteristic luminosity L*, and only weak color changes are detected, consistent with passive evolution. The blue galaxy-luminosity function is more dwarf rich than the red galaxy-luminosity function. No significant change in the comoving density is found in this sample out to z~1.4, assuming that the objects without redshifts (16% of the sample) are galaxies, essentially all of which have z>0.8. This suggests that mergers are not important among the objects in this sample. A population of extremely red objects with (R-K)>5 mag exists in the infrared-selected sample; all four such objects with redshifts are found to be absorption-line galaxies with z~1. Most of the very red objects therefore appear to be galaxies with z≳1 that are not heavily reddened by dust. A measure of the UV extinction at 2400 Å for the emission-line galaxies of a factor of 2 is obtained, implying only modest UV extinction in high-redshift star-forming galaxies.

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