Mathematics – Logic
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........29d&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, BERKELEY, 1994.Source: Dissertation Abstracts International, Volume: 56-05, Section: B
Mathematics
Logic
8
Redshift
Scientific paper
At moderate redshift (z ~ 0.5), powerful radio galaxies are often situated in group and cluster environments. I have carried out a series of imaging investigations aimed at exploring and exploiting this fact. The major goals are: (1) to identify a new sample of distant galaxy clusters for further investigation, (2) to quantify the richnesses of radio galaxy environments, (3) to examine the color distributions of galaxies in radio -selected clusters, and (4) to explore the possibility of using radio selection for extending cluster samples beyond the limits of present optical surveys. Toward this end, I have imaged 42 radio galaxy fields in the redshift range 0.35 < z < 0.8. I present multicolor photometry of galaxies in these fields, as well as similar data on "control field" images not containing radio galaxies. Counts of galaxies around the radio sources, as well as their color distributions, are considered as means of recognizing associated clusters. I quantify the richnesses of the cluster environments, and discuss the colors of the associated cluster galaxies. One radio galaxy at z = 0.620, 3C 220.1, appears to reside in a modest group or poor cluster. High quality images, however, reveal the presence of a large gravitational lens arc around this radio galaxy. I discuss the arc structure, deriving the mass, mass-to-light ratio, and velocity dispersions for the lensing cluster. The existence of large, collapsed masses at high redshift can constrain models for large -scale structure formation. I review the predictions of the biased cold dark matter model and the possible consequences of the 3C 220.1 lens. If radio galaxies are sometimes in rich environments at z ~ 0.5, then perhaps they can be used as signposts for finding still more distant clusters. I present first results from an infrared-optical imaging survey for radio galaxy clusters at z > 1. I find two apparently rich clusters at z = 1.2 which have large populations of very red galaxies. These colors are very similar to those of present-day ellipticals. Apparently, very little spectral evolution has taken place in the reddest galaxies during the last half of the universe's history. The cosmological implications of mature, red elliptical galaxies in a comparatively young universe are briefly considered.
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