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Near-Infrared Spectra of ARP 220: Spatially Resolved CO Absorption in the Inner Kiloparsec

Armus, L. and Neugebauer, G. and Soifer, B. T. and Matthews, K. (1995) Near-Infrared Spectra of ARP 220: Spatially Resolved CO Absorption in the Inner Kiloparsec. Astronomical Journal, 110 (6). pp. 2610-2621. ISSN 0004-6256. doi:10.1086/117718.

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Near-infrared spectra covering λ~2.0-2.5 µm with a spectral resolution of R~80 and a spatial resolution of 0.7" have been obtained from two long slits oriented at a position angle of 96°, centered on and 2.0" south of the two near-infrared nuclei in the ultraluminous infrared galaxy Arp 220. These data have allowed us to determine the strengths of the stellar CO absorption feature and the B γ emission line over the central 7 arcsec (2.5 kpc) on scales of ~250 pc. The two near-infrared nuclei have very strong stellar atmospheric CO absorption coupled with very red H—K colors, implying significant contributions (40%-50%) to the K-band continua from young, red supergiant stars formed in a recent burst of star formation. In contrast to the strong nuclear CO absorption, the equivalent width of the B γ emission line is weak, and peaked at the position of the eastern infrared nucleus where the equivalent width is ~1.0 nm. There is no detectable B γ emission in the spectra extracted from the southern slit. We suggest that the youngest part of the starburst (t~7-8 Myr old) is confined to the Arp 220 nuclei, while the surrounding region (out to at least 2.0"-2.5" radius) is dominated by older stars (~10^8 yr) associated with a previous burst. Together these components are able to account for less than 10% of the bolometric luminosity of Arp 220. The dominant energy source in Arp 220 apparently remains hidden even at 2.2 µm.

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Armus, L.0000-0003-3498-2973
Additional Information:© 1995 American Astronomical Society. Received 1995 April 17; revised 1995 August 9. The W. M. Keck Observatory is operated as a scientific partnership between the California Institute of Technology and the University of California. We thank the entire Keck Observatory staff, especially Wendy Harrison, for making these observations possible. In addition, we thank Tim Heckman and Claus Leitherer for many helpful discussions, and for making their model results available to us prior to publication. We also thank an anonymous referee for many helpful comments which strengthened the presentation of this paper. Infrared astronomy at Caltech is supported by grants from NASA and the NSF. This research has made use of the NASA/IPAC Extragalactic Database which is operated by the Jet Propulsion Laboratory, Caltech, under contract with NASA.
Group:Infrared Processing and Analysis Center (IPAC)
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Issue or Number:6
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Official Citation:Near-Infrared Spectra of ARP 220: Spatially Resolved CO Absorption in the Inner Kiloparsec Armus, L.; Neugebauer, G.; Soifer, B. T.; Matthews, K. Astronomical Journal v.110, p.2610-2621
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74256
Deposited By: Ruth Sustaita
Deposited On:14 Feb 2017 20:22
Last Modified:11 Nov 2021 05:25

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