Redshift z ~ 1 Field Galaxies Observed with the Keck Telescope and the HST

摘要

We report results based on 35 new spectroscopic redshifts obtained with theKeck Telescope for field galaxies that also have photometry and morphology fromsurvey images taken by the refurbished HST. A sample of 24 redshifts forgalaxies fainter than I = 22 has a median redshift of z ~ 0.81. This result isinconsistent with the lower median redshift of z ~ 0.6 predicted by the``maximal merger models'' of Carlberg (1996), which otherwise fit existingdata. The data match an extrapolation of the CFRS, as well as predictions ofcertain mild luminosity-evolution models. Nearly half of the redshifts lie intwo structures at z ~ 0.81 and z ~ 1.0, showing the presence of high densityconcentrations spanning scales of ~ 1/h Mpc, i.e., the size of groups. We findemission lines or the presence of possible neighbors in 7 of 9 otherwiseluminous galaxies with red central regions at redshifts beyond z ~ 0.7. We alsonote a diversity of morphological types among blue galaxies at z ~ 1, includingsmall compact galaxies, ``chains,'' and ``blue nucleated galaxies.'' Thesemorphologies are found among local, but generally less luminous, galaxies.Distant blue galaxies also include apparently normal late-type spirals. Thesefindings could imply modest bursts of star formation caused by mergers orinteractions of small, gas-rich galaxies with each other or with larger,well-formed galaxies. This first glimpse of very faint z ~ 1 field galaxies ofdiverse colors and morphologies suggests that a mixture of physical processesis at work in the formation and evolution of faint field galaxies.