Menéndez-Delmestre, Karín and Blain, Andrew W. and Smail, Ian and Alexander, Dave M. and Chapman, Scott C. and Armus, Lee and Frayer, Dave and Ivison, Rob J. and Teplitz, Harry (2009) Mid-Infrared Spectroscopy of Submillimeter Galaxies: Extended Star Formation in Massive High-redshift Galaxies. Astrophysical Journal, 699 (1). pp. 667-685. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090911-152535061
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We used the Spitzer Infrared Spectrograph (IRS) to study the mid-IR properties and investigate the energetics of 24 Submillimeter Galaxies (SMGs). This is the largest sample of SMGs observed with Spitzer IRS and covers the full extent of properties of the radio-identified population of SMGs in the redshift range of z ~ 0.65-3.2. We observe broad emission features from polycyclic aromatic hydrocarbons in more than 80% of our sample. We find that the median mid-IR spectrum is well described by a starburst component with an additional power law, F_ν ~ ν^(–2), likely representing a <32% contribution from an active galactic nucleus to the bolometric luminosity. Our results thus confirm that starburst activity dominates the bolometric luminosity in SMGs. We find that SMGs show weaker silicate absorption at ~9.7 μm than local ULIRGs. We also find stronger 6.2-μm PAH emission in SMGs (relative to the 7.7 μm PAH feature) than in local nuclear starbursts, which may be attributed to lower extinction by ice along the line of sight to SMGs. This suggests that the continuum and PAH emitting regions of SMGs are less obscured than in local starbursts and similarly luminous low-redshift ULIRGs. We interpret these results as evidence for a more extended distribution of cool and warm dust in SMGs compared to the more compact emitting regions in local ULIRGs and starbursts. Together these results suggest that SMGs are not simple high-redshift analogs of nuclear starbursts or local ULIRGs, but instead they appear to have star formation which resembles that seen in less-extreme star-forming environments at z~0 -suggesting their intense activity is distributed across a far larger region than the ~1 kpc nuclear bursts in local ULIRGs.
|Additional Information:||© 2009 The American Astronomical Society. Received 2008 July 19; accepted 2009 April 2; published 2009 June 15. We thank our anonymous referee for useful comments and suggestions. We are very thankful to Alexandra Pope, Elisabetta Valiante, Anna Sajina, Bernard Brandl and Duncan Farrah for facilitating results and/or reduced spectra of their Spitzer samples for proper comparison to our galaxies in this work. We are also grateful to Laura Hainline, Patrick Ogle, Vandana Desai, and James Geach for helpful discussions. K.M.D. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-0802399. A.W.B. thanks the Research Corporation and the Alfred P. Sloan Foundation. D.M.A. and I.R.S. acknowledge support from the Royal Society. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.|
|Subject Keywords:||galaxies: high-redshift; galaxies: starburst; infrared: galaxies; submillimeter|
|Official Citation:||Mid-Infrared Spectroscopy of Submillimeter Galaxies: Extended Star Formation in Massive High-redshift Galaxies Karín Menéndez-Delmestre, Andrew W. Blain, Ian Smail, Dave M. Alexander, Scott C. Chapman, Lee Armus, Dave Frayer, Rob J. Ivison, and Harry Teplitz 2009 ApJ 699 667-685 doi: 10.1088/0004-637X/699/1/667.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||15 Sep 2009 17:25|
|Last Modified:||26 Dec 2012 11:21|
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