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

Abstract

We have analyzed the data from a large-scale CO survey toward the northern region of the Small Magellanic Cloud (SMC) obtained with the Atacama Compact Array (ACA) stand-alone mode of ALMA. The primary aim of this study is to comprehensively understand the behavior of CO as an H 2 tracer in a low-metallicity environment (Z ∼ 0.2 Z ⊙ ). The total number of mosaic fields is ∼8000, which results in a field coverage of 0.26 degree 2 (∼2.9 ×10 5 pc 2 ), corresponding to ∼10% area of the galaxy. The sensitive ∼2 pc resolution observations reveal the detailed structure of the molecular clouds previously detected in the single-dish NANTEN survey. We have detected a number of compact CO clouds within lower H 2 column density (∼10 20 cm −2 ) regions whose angular scale is similar to the ACA beam size. Most of the clouds in this survey also show peak brightness temperature as low as <1 K, which for optically thick CO emission implies an emission size much smaller than the beam size, leading to beam dilution. The comparison between an available estimation of the total molecular material traced by thermal dust emission and the present CO survey demonstrates that more than ∼90% H 2 gas cannot be traced by the low-J CO emission. Our processed data cubes and 2-D images are publicly available.

Far and extreme UV radiation feedback in molecular clouds and its influence on the mass and size of star clusters

“…In our simulations, we have calculated non-equilibrium chemical reactions of the species, such as CO and H 2 molecules, and C . The spatial distributions of these abundances can be tools to probe the different evolutional stages of the star cluster formation (e.g., Tokuda et al 2021). For example, the cavity structures are formed when the expanding H bubbles trigger the star formation in clouds with 𝑀 cl 10 4 𝑀 .…”