Mapping the Dark Side with DEIMOS: Globular Clusters, X-ray Gas, and Dark Matter in the NGC 1407 Group - AstrophysicsReportar como inadecuado

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Abstract: NGC 1407 is the central elliptical in a nearby evolved galaxy groupapparently destined to become a cluster core. We use the kinematics of globularclusters to probe the dynamics and mass profile of the group-s center, out to60 kpc ~10 R eff - the most extended data set to date around an early-typegalaxy. This sample consists of 172 GC velocities, most of them newly obtainedusing Keck-DEIMOS, with a few additional objects identified as DGTOs or asIGCs. We find weak rotation in the GC system-s outer parts, with the metal-poorand metal-rich GCs misaligned. The RMS velocity profile declines rapidly to aradius of ~20 kpc, and then becomes flat or rising to ~60 kpc. There isevidence that the GC orbits have a tangential bias that is strongest for themetal-poor GCs - possibly contradicting theoretical expectations. We constructcosmologically-motivated galaxy+dark halo dynamical models and infer a masswithin 60 kpc of ~3x10^12 M Sun, extrapolating to a virial mass of ~6x10^13M Sun for a typical LCDM halo - in agreement with results from group galaxykinematics. We present an independent Chandra-based analysis, whose relativelyhigh mass at ~20 kpc disagrees strongly with the GC-based result unless the GCsare assumed to have a peculiar orbit distribution, and we discuss some generalcomparisons between X-ray and optical results. The group-s B-band mass-to-lightratio of ~800 is extreme even for a rich galaxy cluster, much less a poor group- placing it among the most dark matter dominated systems in the universe, andalso suggesting a massive reservoir of baryons lurking in an unseen phase, inaddition to the nonbaryonic dark matter. We compare the kinematical and massproperties of the NGC 1407 group to other nearby groups and clusters, anddiscuss some implications of this system for structure formation.

Autor: Aaron J. Romanowsky, Jay Strader, Lee R. Spitler, Ria Johnson, Jean P. Brodie, Duncan A. Forbes, Trevor Ponman


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