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The opaque nascent starburst in NGC 1377: Spitzer SINGS observations

Roussel, H. and Helou, G. and Smith, J. D. and Draine, B. T. and Hollenbach, D. J. and Moustakas, J. and Spoon, H. W. and Kennicutt, R. C. and Rieke, G. H. and Walter, F. and Armus, L. and Dale, D. A. and Sheth, K. and Bendo, G. J. and Engelbracht, C. W. and Gordon, K. D. and Meyer, M. J. and Regan, M. W. and Murphy, E. J. (2006) The opaque nascent starburst in NGC 1377: Spitzer SINGS observations. Astrophysical Journal, 646 (2). pp. 841-857. ISSN 0004-637X.

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We analyze extensive data on NGC 1377 from the Spitzer Infrared Nearby Galaxies Survey (SINGS). Within the category of nascent starbursts that we previously selected as having infrared-to-radio continuum ratios in large excess of the average and containing hot dust, NGC 1377 has the largest infrared excess yet measured. Optical imaging reveals a morphological distortion suggestive of a recent accretion event. Infrared spectroscopy reveals a compact and opaque source dominated by a hot, self-absorbed continuum (τ~ 20 in the 10μm silicate band). We provide physical evidence against nonstellar activity being the heating source. H II regions are detected through the single [Ne II] line, probing <1% of the ionizing radiation. Not only is the optical depth in different gas and dust phases very high, but >85% of ionizing photons are suppressed by dust. The only other detected emission features are molecular hydrogen lines, arguably excited mainly by shocks, besides photodissociation regions, and weak aromatic bands. The new observations support our interpretation in terms of an extremely young starburst (<1 Myr). More generally, galaxies deficient in radio synchrotron emission are likely observed within a few Myr of the onset of a starburst and after a long quiescence, prior to the replenishment of the interstellar medium with cosmic rays. The similar infrared-radio properties of NGC 1377 and some infrared-luminous galaxies suggest that NGC 1377 constitutes an archetype that will be useful to better understand starburst evolution. Although rare locally because observed in a brief evolutionary stage, nascent starbursts may represent a nonnegligible fraction of merger-induced starbursts that dominate deep infrared counts. Since they differ dramatically from usual starburst templates, they have important consequences for the interpretation of deep surveys.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Helou, G.0000-0003-3367-3415
Smith, J. D.0000-0003-1545-5078
Draine, B. T.0000-0002-0846-936X
Spoon, H. W.0000-0002-8712-369X
Kennicutt, R. C.0000-0001-5448-1821
Rieke, G. H.0000-0003-2303-6519
Walter, F.0000-0003-4793-7880
Armus, L.0000-0003-3498-2973
Dale, D. A.0000-0002-5782-9093
Sheth, K.0000-0002-5496-4118
Murphy, E. J.0000-0001-7089-7325
Additional Information:© 2006 The American Astronomical Society. Received 2006 March 5; accepted 2006 April 11. We wish to thank Marc Sauvage for fruitful discussions, Mark Wolfire for tirelessly running photodissociation region models to help interpret the data, and Nancy Silbermann for the timely scheduling of the Spitzer IRS observations. Support for this work, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through an award issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:dust, extinction—galaxies: evolution—galaxies: individual (NGC 1377)—galaxies: ISM—galaxies: starburst—infrared: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:ROUapj06
Persistent URL:
Official Citation:H. Roussel et al 2006 ApJ 646 841
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5941
Deposited By: Lindsay Cleary
Deposited On:09 Nov 2006
Last Modified:09 Mar 2020 13:18

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