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K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC

A. M. Gilbert·J. R. Graham·I. S. McLean·E. E. Becklin·D. F. Figer·J. E. Larkin·N. A. Levenson·H. I. Teplitz·M. K. Wilcox
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Abstract

We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039) with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the vicinity of the southern nucleus (NGC 4039) in 0.39" seeing in K-band using NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the highest surface brightness peak in the mid-IR (12-18 um) ISO image presented by Mirabel et al (1998). We obtained high signal-to-noise 2.03-2.45 um spectra of the nucleus and the obscured star cluster at R = 1900. The cluster is very young (age ~ 4 Myr), massive (M ~ 16E6 M_sun), and compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius), assuming a Salpeter IMF (0.1-100 M_sun). Its hot stars have a radiation field characterized by T_eff ~ 39,000 K, and they ionize a compact HII region with n_e ~ 10^4 cm^(-3). The stars are deeply embedded in gas and dust (A_V = 9-10 mag), and their strong FUV field powers a clumpy photodissociation region with densities n_H > 10^5 cm^(-3) on scales of ~ 200 pc, radiating L{H_2 1-0 S(1)}= 9600 L_sun.

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A. M. Gilbert, J. R. Graham, I. S. McLean, E. E. Becklin, D. F. Figer, J. E. Larkin, N. A. Levenson, H. I. Teplitz, M. K. Wilcox. 2000-02-17. K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC. https://arxiv.org/abs/astro-ph/0002357

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