Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995pasp..107..797e&link_type=abstract
Publications of the Astronomical Society of the Pacific, v.107, p.797
Astronomy and Astrophysics
Astronomy
Scientific paper
More than a decade of galaxy surveys have produced a unified picture in which luminous matter is distributed in clusters and superclusters of galaxies connected by filamentary structures and surrounding large voids. Many studies have also provided considerable evidence that the properties of galaxies depend on their environment. However, disagreement remains over whether the environmental differences arise from conditions at the time when the galaxies formed or from their subsequent evolution. Part of the confusion is due to the effect of galaxy clusters, since they contain a wide range of galaxy densities and could be responsible for the observed environmental dependencies even at low density. In this thesis we examined the dependence of the large scale distribution of galaxies on galaxy color. We carried out a medium deep (b_J <~ 20) multi-pencil-beam redshift survey at the North Galactic Pole in nine 40 arcminute fields spanning a 5 degrees X 5 degrees area. This survey was conducted initially to check the discovery by Broadhurst et. al. (Nature, 343, 726, 1990) of strong and apparently periodic structure, and showed that peaks detected in their Northern survey appear to be due to transverse structures rather than due to galaxy clusters. Our final catalog contains 307 galaxies with redshifts and colors, to which we added 46 galaxies from an existing survey. By treating the pencil-beams as a one dimensional probe along the line of sight we determine the extent to which the galaxies in these structures are segregated by color. We used the statistical technique of measuring moments of counts in cells to study how the fluctuations of galaxy counts changed with scale. We first divided the galaxy sample into red and blue halves and found that the fluctuations in the red galaxy distribution were stronger than those of the blue on all scales out to 60 h^-1_50 Mpc. This result suggests that the structures are dominated by the red galaxies. We checked that this effect was not caused entirely by the two largest structures in our survey by removing them from the sample and repeating the moment calculations. We also examined whether the difference in the galaxy distributions represented a continuous trend with color or were merely due to the clustering of the reddest galaxies. After dividing the sample into three color subgroups and comparing their moments, we found that the moments of the yellow galaxies are indeed intermediate between those of the red and blue galaxies. Finally, we tested the extent to which the difference between the red and blue galaxy distributions was due to small-scale clustering. We measured a modified second moment from which we remove the contribution of galaxy pairs contained within a single beam, thereby eliminating the effect of small-scale correlations. We found that, while there remained a difference between the red and blue galaxy distributions, its significance was substantially decreased, which suggests that the dominant contribution to the color segregation is small-scale clustering within the transverse structures. Overall, our results imply that color segregation of galaxies occurs primarily on scales over which they can be explained by environmentally dependent evolutionary processes, such as galaxy-galaxy and galaxy-IGM interactions, rather than the conditions under which the galaxies formed. (SECTION: Dissertation Summaries)
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