Color bimodality: implications for galaxy evolution

Ivan K. Baldry, Michael L. Balogh, R. G. Bower, K. Glazebrook, Robert C. Nichol

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We use a sample of 69726 galaxies from the SDSS to study the variation of the bimodal color‐magnitude (CM) distribution with environment. Dividing the galaxy population by environment (Σ5) and luminosity (−23 < Mr < −17), the u − r color functions are modeled using double‐Gaussian functions. This enables a deconvolution of the CM distributions into two populations: red and blue sequences. The changes with increasing environmental density can be separated into two effects: a large increase in the fraction of galaxies in the red distribution, and a small color shift in the CM relations of each distribution. The average color shifts are 0.05 ± 0.01 and 0.11 ± 0.02 for the red and blue distributions, respectively, over a factor of 100 in projected neighbor density. The red fraction varies between about 0% and 70% for low‐luminosity galaxies and between about 50% and 90% for high‐luminosity galaxies. This difference is also shown by the variation of the luminosity functions with environment. We demonstrate that the effects of environment and luminosity can be unified. A combined quantity, Σmod = (Σ5/Mpc−2) + (Lr/L−20.2), predicts the fraction of red galaxies, which may be related to the probability of transformation events. Our results are consistent with major interactions (mergers and/or harassment) causing galaxies to transform from the blue to the red distribution. We discuss this and other implications for galaxy evolution from earlier results and model the effect of slow transformations on the color functions. © 2004 American Institute of Physics
Original languageEnglish
Title of host publicationThe new cosmology
Subtitle of host publicationconference on strings and cosmology; the Mitchell Symposium on Observational Cosmology
EditorsRoland E. Allen, Dimitri V. Nanopoulos, Christopher N. Pope
Place of PublicationMelville, N.Y.
PublisherAmerican Institute of Physics
ISBN (Print) 0735402272
Publication statusPublished - 2004
EventThe New Cosmology: Conference on Strings and Cosmology; The Mitchell Symposium on Observational Cosmology - College Station, Texas, United States
Duration: 1 Apr 2004 → …

Publication series

NameAIP conference proceedings


ConferenceThe New Cosmology
Country/TerritoryUnited States
Period1/04/04 → …


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