The Dust-selected Molecular Clouds in the Northeast Region of the Small Magellanic Cloud*

Abstract

We present a high-sensitivity (1σ < 1.6 mJy beam −1 ) continuum observation in a 343 arcmin 2 area of the northeast region in the Small Magellanic Cloud at a wavelength of 1.1 mm, conducted using the AzTEC instrument on the ASTE telescope. In the observed region, we identified 20 objects by contouring 10σ emission. Through spectral energy distribution (SED) analysis using 1.1 mm, Herschel, and Spitzer data, we estimated the gas masses of 5 × 10 3 -7 × 10 4 M , assuming a gas-to-dust ratio of 1000. Dust temperature and the index of emissivity were also estimated as 18-33 K and 0.9-1.9, respectively, which are consistent with previous low resolution studies. The relation between dust temperature and the index of emissivity shows a weak negative linear correlation. We also investigated five CO-detected dust-selected clouds in detail. The total gas masses were comparable to those estimated from the Mopra CO data, indicating that the assumed gas-to-dust ratio of 1000 and the X CO factor of 1 × 10 21 cm −2 (K km s −1 ) −1 , with uncertainties of a factor of 2, are reliable for the estimation of the gas masses of molecular or dust-selected clouds. Dust column density showed good spatial correlation with CO emission, except for an object that associates with bright young stellar objects. The 8 µm filamentary and clumpy structures also showed similar spatial distribution with the * Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. I. Overview: CO Cloud Distributions

“…The millimeter continuum emission is useful to probe the presence of massive/dense clumps around a massive protostar. The total 1.3 mm flux of MMS-2 infers that the gas mass is ∼6 ×10 3 M ⊙ assuming the gas-to-dust ratio of 1000 (e.g., Roman-Duval et al 2014), dust opacity of 1 cm −2 g −1 (e.g., Ossenkopf & Henning 1994), and dust temperature of 24 K (Takekoshi et al 2018).…”

“…Spitzer/Herschel observations provided a high-dynamic-range view of cold/warm gas (Bolatto et al 2007(Bolatto et al , 2011Gordon et al 2011Gordon et al , 2014Jameson et al 2016) as well as the young stellar population (e.g., Oliveira et al 2013;Sewi lo et al 2013;Ruffle et al 2015). Ground-based observations detected millimeter/submillimeter dust continuum emission from not only bright CO clouds (Bot et al 2010;Hony et al 2015;Takekoshi et al 2017Takekoshi et al , 2018) but also fainter clouds, which are likely to be cold molecular material that was not accessible with the previous CO surveys (Takekoshi et al 2017). The newly developed Australian Square Kilometre Array Pathfinder (ASKAP) interferometer has been updating the atomic hydrogen (H i) view in the SMC.…”