K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC
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 (MK(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 Msun), and compact (density ~ 115 Msun pc(-3) within a 32 pc half-light radius), assuming a Salpeter IMF (0.1-100 Msun). Its hot stars have a radiation field characterized by Teff ~ 39,000 K, and they ionize a compact HII region with ne ~ 104 cm(-3). The stars are deeply embedded in gas and dust (AV = 9-10 mag), and their strong FUV field powers a clumpy photodissociation region with densities nH > 105 cm(-3) on scales of ~ 200 pc, radiating LH2 1-0 S(1)= 9600 Lsun.
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