Absence of Dwarf Galaxies at High Redshifts Evidence from a Galaxy Group.pdf

Absence of Dwarf Galaxies at High Redshifts Evidence from a Galaxy Group.pdf

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Absence of Dwarf Galaxies at High Redshifts Evidence from a Galaxy Group

a r X i v : a s t r o - p h / 0 4 0 8 1 4 4 v 1 9 A u g 2 0 0 4 Draft version February 2, 2008 Preprint typeset using LATEX style emulateapj v. 14/09/00 ABSENCE OF DWARF GALAXIES AT HIGH REDSHIFTS: EVIDENCE FROM A GALAXY GROUP William G. Mathews1, Laura Chomiuk1, Fabrizio Brighenti12, David A. Buote3 Draft version February 2, 2008 ABSTRACT The galaxy group NGC 5044 consists of a luminous giant elliptical galaxy surrounded by a cluster of ~ 160 low luminosity and dwarf galaxies, mostly of early type. The cumulative projected radial distribution of dwarf galaxies in the NGC 5044 group, unlike distributions of more luminous galaxies in rich clusters, does not follow a projected dark matter (NFW) profile. A deficiency or absence of low luminosity galaxies is apparent in NGC 5044 within about 350 kpc. Most of the dwarf galaxies in NGC 5044 entered the virial radius at redshifts z ~ 2 ? 3(af/0.25), where af = 1/(1 + zf ) is the epoch of group formation, and very few entered during redshifts z ~ 2 ? 3(af/0.25). The peculiar, non-NFW shape of the projected cumulative dwarf galaxy distribution in NGC 5044 within 350 kpc resembles the characteristic cumulative distribution of dark subhalos that are also known to be relatively young. Dynamical friction is unlikely to explain the apparent lack of group member galaxies at small radii in NGC 5044. Subject headings: galaxies: elliptical and lenticular, CD – galaxies: dwarfs – clusters – groups – feedback 1. introduction The early evolution of dwarf galaxies is of interest be- cause of the possible great antiquity of these galaxies and because they lie near the lowest mass scale for hierarchi- cal assembly in which low mass galaxies merge to form normal galaxies of larger mass. Efforts to understand the evolution of these faint galaxies have been frustrated be- cause of the difficulty of direct observation at cosmolog- ically relevant redshifts. Theoretical models of the for- mation of dwarf galaxies are complicated by the po

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