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Title:
Obscured Star Formation in the Central Region of the Dwarf Galaxy NGC 5253
Authors:
Alonso-Herrero, Almudena; Takagi, Toshinobu; Baker, Andrew J.; Rieke, George H.; Rieke, Marcia J.; Imanishi, Masatoshi; Scoville, Nick Z.
Affiliation:
AA(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; and Departamento de Astrofísica Molecular e Infrarroja, IEM, Consejo Superior de Investigaciones Científicas, Serrano 113b, 28006 Madrid, Spain), AB(Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, Kent CT2 7NR, UK), AC(Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, D-85741 Garching, Germany), AD(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721), AE(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721), AF(National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan), AG(Astronomy Department, MS 105-24, California Institute of Technology, Pasadena, CA 91125)
Publication:
The Astrophysical Journal, Volume 612, Issue 1, pp. 222-237. (ApJ Homepage)
Publication Date:
09/2004
Origin:
UCP
ApJ Keywords:
Galaxies: Dwarf, Galaxies: Individual: NGC Number: NGC 5253, Galaxies: Nuclei, Galaxies: Star Clusters, Galaxies: Starburst
DOI:
10.1086/422448
Bibliographic Code:
2004ApJ...612..222A

Abstract

We present Hubble Space Telescope (HST) NICMOS observations (1.1-2.2 μm) and 1.9-4.1 μm spectroscopy of the central region of the dwarf galaxy NGC 5253. The HST NICMOS observations reveal the presence of a nuclear double star cluster separated by ~=0.3"-0.4", or 6-8 pc (for a distance d=4.1 Mpc). The double star cluster, also a bright double source of Paα emission, appears to be coincident with the double radio nebula detected at 1.3 cm. The eastern near-infrared star cluster (C1) is identified with the youngest optical cluster, whereas the western star cluster (C2), although it is almost completely obscured in the optical, becomes the brightest star cluster in the central region of NGC 5253 at wavelengths longer than 2 μm. Both clusters are extremely young, with ages of approximately 3.5 Myr. C2 is more massive than C1 by a factor of 6-20 (MC2=7.7×105-2.6×106 Msolar, for a Salpeter initial mass function [IMF] in the mass range 0.1-100 Msolar). Analysis of the circumnuclear spectrum excluding C1 and C2, as well as of a number of other near-infrared-selected clusters with a range of (young) ages, suggests that the star formation was triggered across the central regions of the galaxy. We have also modeled the nuclear UV to mid-infrared spectral energy distribution (SED) of NGC 5253 and found that the infrared part is well modeled by a highly obscured (AV=17 mag) young starburst with a stellar mass consistent with our photometric estimates for C1 and C2. The SED model predicts a moderately bright polycyclic aromatic hydrocarbon (PAH) feature at 3.3 μm that is not detected in our nuclear L-band spectrum. NGC 5253's low metallicity and a top-heavy IMF likely combine to suppress the 3.3 μm PAH emission that is commonly seen in more massive starburst systems.

Based on observations with the NASA/ESA Hubble Space Telescope (HST), obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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