Journal
ASTROPHYSICAL JOURNAL
Volume 714, Issue 2, Pages 1779-1788Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/714/2/1779
Keywords
galaxies: clusters: general; galaxies: elliptical and lenticular, cD; galaxies: formation; galaxies: fundamental parameters; galaxies: general; galaxies: statistics; galaxies: structure
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We provide a physical interpretation and explanation of the morphology-density relation for galaxies, drawing on stellar masses, star formation rates, axis ratios, and group halo masses from the Sloan Digital Sky Survey. We first re-cast the classical morphology-density relation in more quantitative terms, using low star formation rate (quiescence) as a proxy for early-type morphology and dark matter halo mass from a group catalog as a proxy for environmental density: for galaxies of a given stellar mass the quiescent fraction is found to increase with increasing dark matter halo mass. Our novel result is that-at a given stellar mass-quiescent galaxies are significantly flatter in dense environments, implying a higher fraction of disk galaxies. Supposing that the denser environments differ simply by a higher incidence of quiescent disk galaxies that are structurally similar to star-forming disk galaxies of similar mass, explains simultaneously and quantitatively these quiescence-environment and shape-environment relations. Our findings add considerable weight to the slow removal of gas as the main physical driver of the morphology-density relation, at the expense of other explanations.
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