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Preprint typeset using L ATEX style emulateapj v. 11/12/01 THE RECENT AND CONTINUING ASSEMBLY OF FIELD ELLIPTICALS BY RED MERGERS

By Pieter G. Van Dokkum

Abstract

We present a study of tidal debris associated with 126 nearby red galaxies, selected from the 1.2 degree 2 Multiwavelength Survey by Yale-Chile (MUSYC) and the 9.3 degree 2 NOAO Deep Wide-Field Survey. In the full sample 67 galaxies (53 %) show morphological signatures of tidal interactions, consisting of broad fans of stars, tails, and other asymmetries at very faint surface brightness levels. When restricting the sample to the 86 bulge-dominated early-type galaxies the fraction of tidally disturbed galaxies rises to 71 %, which implies that for every “normal ” undisturbed elliptical there are two which show clear signs of interactions. The tidal features are red and smooth, and often extend over> 50 kpc. Of the tidally distorted galaxies about 2/3 are remnants and 1/3 are interacting with a companion galaxy. The companions are usually bright red galaxies as well: the median R-band luminosity ratio of the tidal pairs is 0.31, and the median color difference after correcting for the slope of the color-magnitude relation is −0.02 in B − R. If the ongoing mergers are representative for the progenitors of the remnants ∼ 35 % of bulge-dominated galaxies experienced a merger with mass ratio> 1: 4 in the recent past. With further assumptions it is estimated that the present-day mass accretion rate of galaxies on the red sequence ∆M/M = 0.09 ± 0.04 Gyr −1. For a constant or increasing mass accretion rate with redshift, we find that red mergers may lead to an evolution of a factor of ∼> 2 in the stellar mass density in luminous red galaxie

Year: 2005
OAI identifier: oai:CiteSeerX.psu:10.1.1.317.7721
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