03/06/2009 – 14h – Auditório Principal, Bloco G – IAG/USP

Renato Dupke

ON/MCT & Univ. of Michigan

Título/Title: On the nature fossil groups of galaxies

Resumo/Abstract:

Fossil groups are X-ray bright galaxy systems that present an unusual lack of luminous galaxies in the inner regions, except for a giant central galaxy. They present a puzzle to current theories of structure formation. Their high velocity dispersions and high intragroup gas temperatures indicate cluster-like potential wells, despite the low number of bright galaxies. Most of the measured concentration parameters seem very high indicating early formation epochs; however, they seem to lack significant cooling cores. The lack of good quality X-ray data may enhance these apparent contradictions. The standard explanation for their formation suggests that bright galaxies within half the virial radii of these systems were wiped out by cannibalism forming the central galaxy. The lack of significant cooling cores would imply that some extra heating is taken place near the center of the group. It is unlikely that they are caused by AGNs given the well behaved smooth appearance of the X-ray distribution, so that galactic winds seem to be the most likely heating source. Since dry mergers, typically invoked to explain the formation of the central galaxies, are not expected to change the IGM energetics significantly (thus not preventing the formation of cooling cores), we investigate the scenario where recent gaseous (wet) mergers formed the central galaxy injecting energy and changing the chemistry of the IGM in fossil groups. I will present preliminary results of a test for the type of merger that formed the central group galaxy, by measuring the expected change in the chemistry and energetics of the intergalactic gas associate to gasless (dry) and gaseous (wet) mergers.

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