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Date and Time of the Query: 2019-05-21 T08:26:32 PDT
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For refcode 2007ApJ...658.1027L:
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Copyright by American Astronomical Society. Reproduced by permission
2007ApJ...658.1027L The Spitzer Survey of the Small Magellanic Cloud: Far-Infrared Emission and Cold Gas in the Small Magellanic Cloud Adam Leroy, Alberto Bolatto, Snezana Stanimirovic, Norikazu Mizuno, Frank Israel, and Caroline Bot Abstract. We present new FIR maps of the SMC at 24, 70, and 160 micron 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_=3x10^5^M_sun_, 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__=3.2x10^7^M_sun_ 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)x10^21^cm^-2^(Kkms^-1^)^-1^. Over the volume occupied by CO the conversion factor is lower, X_CO_=(6+/-1)x10^21^cm^-2^(Kkms^-1^)^-1^, but still a few times larger than that found using virial mass methods. The molecular peaks have H_2_ surface densities {SIGMA}_H_2__~180+/-30M_sun_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. Key words: ISM: Dust, Extinction, Galaxies: ISM, Infrared: ISM, ISM: Molecules, Galaxies: Magellanic Clouds
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