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Stellar Populations in the Central 0.5 pc of the Galaxy. I. A New Method for Constructing Luminosity Functions and Surface-density Profiles

Do, T. and Lu, J. R. and Ghez, A. M. and Morris, M. R. and Yelda, S. and Martinez, G. D. and Wright, S. A. and Matthews, K. (2013) Stellar Populations in the Central 0.5 pc of the Galaxy. I. A New Method for Constructing Luminosity Functions and Surface-density Profiles. Astrophysical Journal, 764 (2). Art. No. 154. ISSN 0004-637X.

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We present new high angular resolution near-infrared spectroscopic observations of the nuclear star cluster surrounding the Milky Way's central supermassive black hole. Using the integral-field spectrograph OSIRIS on Keck II behind the laser-guide-star adaptive optics system, this spectroscopic survey enables us to separate early-type (young, 4-6 Myr) and late-type (old, >1 Gyr) stars with a completeness of 50% down to K' = 15.5 mag, which corresponds to ~10 M_☉ for the early-type stars. This work increases the radial extent of reported OSIRIS/Keck measurements by more than a factor of three from 4" to 14" (0.16 to 0.56 pc), along the projected disk of young stars. For our analysis, we implement a new method of completeness correction using a combination of star-planting simulations and Bayesian inference. We assign probabilities for the spectral type of every source detected in deep imaging down to K' = 15.5 mag using information from spectra, simulations, number counts, and the distribution of stars. The inferred radial surface-density profiles, Σ(R)∝ R^(-Γ), for the young stars and late-type giants are consistent with earlier results (Γ_(early) = 0.93 ± 0.09, Γ_(late) = 0.16 ± 0.07). The late-type surface-density profile is approximately flat out to the edge of the survey. While the late-type stellar luminosity function is consistent with the Galactic bulge, the completeness-corrected luminosity function of the early-type stars has significantly more young stars at faint magnitudes compared with previous surveys with similar depth. This luminosity function indicates that the corresponding mass function of the young stars is likely less top-heavy than that inferred from previous surveys.

Item Type:Article
Related URLs:
URLURL TypeDescription
Do, T.0000-0001-9554-6062
Lu, J. R.0000-0001-9611-0009
Ghez, A. M.0000-0003-3230-5055
Morris, M. R.0000-0002-6753-2066
Yelda, S.0000-0001-5036-4329
Martinez, G. D.0000-0002-7476-2521
Wright, S. A.0000-0003-1034-8054
Additional Information:© 2013 American Astronomical Society. Received 2012 September 20; accepted 2012 December 21; published 2013 February 1. The authors thank the staff of the Keck observatory, especially Randy Campbell, Al Conrad, and Jim Lyke, for all their help in obtaining the new observations, Rainer Schödel for providing us with an extinction map of the Galactic center region, and Annika Peter for discussions about the Bayes factor. This work has been supported by a TMT postdoctoral fellowship (T.D.), an NSF Astronomy & Astrophysics Postdoctoral Fellowship (AST-1102791; J.R.L.), NSF grant AST-0909218 (PI: A.M.G.), and the Levine-Leichtman family foundation. The infrared data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Keck:II (OSIRIS, NIRC2)
Funding AgencyGrant Number
TMT postdoctoral fellowshipUNSPECIFIED
NSF Astronomy and Astrophysics Postdoctoral FellowshipAST-1102791
Levine-Leichtman Family FoundationUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:Galaxy: center; infrared: stars; stars: early-type; stars: luminosity function, mass function; techniques: high angular resolution; techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20130401-112427405
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Official Citation:Stellar Populations in the Central 0.5 pc of the Galaxy. I. A New Method for Constructing Luminosity Functions and Surface-density Profiles T. Do et al. 2013 ApJ 764 154
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37702
Deposited By: Ruth Sustaita
Deposited On:01 Apr 2013 18:45
Last Modified:01 Nov 2019 19:55

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