Arnold, Jacob A. and Romanowski, Aaron J. and Brodie, Jean P. and Chomiuk, Laura and Spitler, Lee R. and Strader, Jay and Benson, Andrew J. and Forbes, Duncan A. (2011) The Fossil Record of Two-phase Galaxy Assembly: Kinematics and Metallicities in the Nearest S0 Galaxy. Astrophysical Journal Letters, 736 (2). Art. No. L26. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110830-081227632
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We present a global analysis of kinematics and metallicity in the nearest S0 galaxy, NGC 3115, along with implications for its assembly history. The data include high-quality wide-field imaging from Suprime-Cam on the Subaru telescope, and multi-slit spectra of the field stars and globular clusters (GCs) obtained using Keck-DEIMOS/LRIS and Magellan-IMACS. Within two effective radii, the bulge (as traced by the stars and metal-rich GCs) is flattened and rotates rapidly (v/σ ≳ 1.5). At larger radii, the rotation declines dramatically to v/σ ~ 0.7, but remains well aligned with the inner regions. The radial decrease in characteristic metallicity of both the metal-rich and metal-poor GC subpopulations produces strong gradients with power-law slopes of –0.17 ± 0.04 and –0.38 ± 0.06 dex dex^(–1), respectively. We argue that this pattern is not naturally explained by a binary major merger, but instead by a two-phase assembly process where the inner regions have formed in an early violent, dissipative phase, followed by the protracted growth of the outer parts via minor mergers with typical mass ratios of ~15-20:1.
|Additional Information:||© 2011 The American Astronomical Society. Received 2011 January 29; accepted 2011 May 27; published 2011 July 7. We thank Andi Burkert, Avishai Dekel, Loren Hoffman, Chris Moody, and Joel Primack for useful discussions, the referee Igor Chilingarian for helpful comments, and Ewan O’Sullivan for contributing observing time. Based in part on data collected at Subaru Telescope (operated by the National Astronomical Observatory of Japan) via a Gemini Observatory time exchange (GN-2008A-C-12), and also the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Some of the data presented herein were obtained at the W. M. Keck Observatory, operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration, and made possible by the generous financial support of the W. M. Keck Foundation. This material is based upon work supported by the National Science Foundation under Grants AST-0808099 and AST-0909237 and a Graduate Research Fellowship, and also by the UCSC University Affiliated Research Center’s Aligned Research Program. A.J.R. was further supported by the FONDAP Center for Astrophysics CONICYT 15010003. A.J.B. acknowledges the support of the Gordon and Betty Moore Foundation. L.C. is a Jansky Fellow at the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We acknowledge financial support from the Access to Major Research Facilities Programme, a component of the International Science Linkages Programme established under the Australian Government’s innovation statement, Backing Australia’s Ability.|
|Subject Keywords:||galaxies: bulges; galaxies: formation; galaxies: halos; galaxies: individual (NGC 3115); galaxies: kinematics and dynamics; globular clusters: general|
|Classification Code:||PACS: 98.52.Lp; 98.62.Dm; 98.65.Fz; 98.20.Gm|
|Official Citation:||The Fossil Record of Two-phase Galaxy Assembly: Kinematics and Metallicities in the Nearest S0 Galaxy Jacob A. Arnold et al. 2011 ApJ 736 L26|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||30 Aug 2011 16:24|
|Last Modified:||26 Dec 2012 13:38|
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