Lahuis, F. and Spoon, H. W. W. and Tielens, A. G. G. M. and Doty, S. D. and Armus, L. and Charmandaris, V. and Houck, J. R. and Stäuber, P. and van Dishoeck, E. F. (2007) Infrared Molecular Starburst Fingerprints in Deeply Obscured (Ultra)Luminous Infrared Galaxy Nuclei. Astrophysical Journal, 659 (1). pp. 296-304. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20100204-151002690
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High-resolution spectra of the Spitzer Space Telescope show vibration-rotation absorption bands of gaseous C_2H_2, HCN, and CO_2 molecules toward a sample of deeply obscured (U)LIRG nuclei. The observed bands reveal the presence of dense (n ≳ 10^7 cm^(-3)), warm (T_(ex) = 200-700 K) molecular gas with high column densities of these molecules ranging from a few 10^(15) to 10^(17) cm^(-2). Abundances relative to H_2, inferred from the silicate optical depth, range from ~10^(-7) to 10^(-6) and show no correlation with temperature. Theoretical studies show that the high abundances of both C_2H_2 and HCN exclude an X-ray dominated region (XDR) associated with the toroid surrounding an AGN as the origin of this dense warm molecular gas. Galactic massive protostars in the so-called hot-core phase have similar physical characteristics with comparable high abundances of C_2H_2, HCN, and CO_2 in the hot phase. However, the abundances of C_2H_2 and HCN and the C_2H_2/CO_2 and HCN/CO_2 ratios are much higher toward the (U)LIRGs in the cooler (T_(ex) ≾ 400 K) phase. We suggest that the warm dense molecular gas revealed by the mid-IR absorption lines is associated with a phase of deeply embedded star formation, where the extreme pressures and densities of the nuclear starburst environment have inhibited the expansion of H II regions and the global disruption of the star-forming molecular cloud cores and have "trapped" the star formation process in an "extended" hot-core phase.
|Additional Information:||© 2007 The American Astronomical Society. Received 2006 October 19; accepted 2006 December 21. The authors would like to thank Tom Geballe for sharing early results and the CO data of IRAS 08572+3915 NW; John Lacy and Claudia Knez for sharing the TEXES data; and Bernhard Brandl, Kees Dullemond, Masa Imanishi, David Rupke, and Marco Spaans for many useful discussions. Astrochemistry in Leiden is supported by a Spinoza grant from NWO.|
|Subject Keywords:||galaxies : ISM; galaxies : nuclei; infrared : ISM; ISM : evolution; ISM : molecules|
|Official Citation:||Infrared Molecular Starburst Fingerprints in Deeply Obscured (Ultra)Luminous Infrared Galaxy Nuclei F. Lahuis, H. W. W. Spoon, A. G. G. M. Tielens, S. D. Doty, L. Armus, V. Charmandaris, J. R. Houck, P. Stäuber, and E. F. van Dishoeck 2007 ApJ 659 296-304 doi: 10.1086/512050|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||08 Feb 2010 20:44|
|Last Modified:||26 Dec 2012 11:44|
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