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The Spitzer Survey of the Small Magellanic Cloud: Far-Infrared Emission and Cold Gas in the Small Magellanic Cloud

Leroy, Adam and Bolatto, Alberto and Stanimirovic, Snezana and Mizuno, Norikazu and Israel, Frank and Bot, Caroline (2007) The Spitzer Survey of the Small Magellanic Cloud: Far-Infrared Emission and Cold Gas in the Small Magellanic Cloud. Astrophysical Journal, 658 (2). pp. 1027-1046. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20100423-094434195

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Abstract

We present new FIR maps of the SMC at 24, 70, and 160 μm obtained as part of the Spitzer Survey of the Small Magellanic Cloud (S^(3)MC). These maps cover most of the star formation in the SMC bar and wing. We combine our maps with literature data to derive the dust mass surface density across the SMC. We find a total dust mass of M_(dust) = 3 × 10^5 M_☉, implying a dust-to-hydrogen ratio over the region studied of log_(10)(D/H) = -2.86, or 1 : 700, which includes H_2. Assuming the dust to trace the total gas column, we derive H_2 surface densities across the SMC. We find a total H_2 mass M_(H_2) = 3.2 × 10^7 M_☉ in a distribution similar to that of the CO, but more extended. We compare profiles of CO and H_2 around six molecular peaks; on average H_2 is more extended than CO by a factor of ~1.3. The implied CO-to-H_2 conversion factor over the whole SMC is X_(CO) = (13 ± 1) × 10^(21) cm^(-2) (K km s^(-1))^(-1). Over the volume occupied by CO the conversion factor is lower, X_(CO) = (6 ± 1) × 10^(21) cm^(-2) (K km s^(-1))^(-1), but still a few times larger than that found using virial mass methods. The molecular peaks have H_2 surface densities Σ_(H_2) ≈ 180 ± 30 M pc^(-2), similar to those in Milky Way GMCs, and correspondingly low extinctions, A_V ~ 1-2 mag. The theory of photoionization-regulated star formation predicts A_V ~ 6, which would require the GMCs to be ~3 times smaller than our 46 pc resolution element. For a given hydrostatic gas pressure, the SMC has a 2-3 times lower ratio of molecular to atomic gas than spiral galaxies. Combined with lower mean densities, this results in this galaxy having only 10% of its gas in the molecular phase.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1086/511150DOIArticle
http://iopscience.iop.org/0004-637X/658/2/1027PublisherArticle
ORCID:
AuthorORCID
Leroy, Adam0000-0002-2545-1700
Bolatto, Alberto0000-0002-5480-5686
Additional Information:© 2007 American Astronomical Society. Received 2006 August 21; accepted 2006 November 15. This work is based 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. This research was partially supported by NSF grant AST 02-28963. Partial support for this work was also provided by NASA through an award issued by JPL/Caltech (NASA-JPL Spitzer grant 1264151 awarded to Cycle 1 project 3316). We made use of the NASA/ IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration; and NASA’s Astrophysics Data System (ADS). This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We wish to especially thank L. Blitz, C. McKee, and J. Graham, who all gave critical readings of this work while it was being prepared as part of A. L.’s thesis, and F. Boulanger, who kindly provided suggestions on reading a draft. We also thank the anonymous referee for suggestions that improved this work.
Funders:
Funding AgencyGrant Number
NSFAST 02-28963
NASA/JPL/Caltech1264151
Subject Keywords:dust, extinction; galaxies: ISM; infrared: ISM; ISM: molecules; Magellanic Clouds
Record Number:CaltechAUTHORS:20100423-094434195
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20100423-094434195
Official Citation:Adam Leroy et al 2007 ApJ 658 1027 doi: 10.1086/511150
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18052
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:23 Apr 2010 21:12
Last Modified:02 Nov 2017 21:43

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