The G332 molecular cloud ring: I. Morphology and physical characteristics

Abstract

We present a morphological and physical analysis of a Giant Molecular Cloud (GMC) using the carbon monoxide isotopologues (${}^{12}$CO, ${}^{13}$CO, C${}^{18}$O ${}^3{P}_2\to$ ${}^3{P}_1$) survey of the Galactic Plane (Mopra CO Southern Galactic Plane Survey), supplemented with neutral carbon maps from the HEAT telescope in Antarctica. The giant molecular cloud structure (hereinafter the ring) covers the sky region $332^{\circ }$ < $\ell$ < $333^{\circ }$ and $b$ = $\pm 0.5^{\circ }$ (hereinafter the G332 region). The mass of the ring and its distance are determined to be respectively ~2$\times 10^5{\mathrm{M}}_{\odot }$ and ~3.7 kpc from Sun. The dark molecular gas fraction, estimated from the ${}^{13}$CO and [CI] lines, is $\sim 17\%$ for a CO T${}_{\mathrm{ex}}$ between [10,20 K]. Comparing the [CI] integrated intensity and N(H${}_2$) traced by ${}^{13}$CO and ${}^{12}$CO, we define an X${}_{\mathrm{CI}}^{809}$ factor, analogous to the usual X${}_{\mathrm{co}}$, through the [CI] line. X${}_{\mathrm{CI}}^{809}$ ranges between [1.8,2.0]$\times 10^{21}{\mathrm{cm}}^{-2}{\mathrm{K}}^{-1}{\mathrm{km}}^{-1}\mathrm{s}$. We examined local variation in X${}_{\mathrm{co}}$ and T${}_{\mathrm{ex}}$ across the cloud, and find in regions where the star formation activity is not in an advanced state, an increase in the mean and dispersion of the X${}_{\mathrm{co}}$ factor as the excitation temperature decreases. We present a catalogue of C${}^{18}$O clumps within the cloud. The star formation (SF) activity ongoing in the cloud shows a correlation with T${}_{\mathrm{ex}}$, [CI] and CO emissions, and anti-correlation with X${}_{\mathrm{co}}$, suggesting a North-South spatial gradient in the SF activity. We propose a method to disentangle dust emission across the Galaxy, using HI and ${}^{13}$CO data. We describe Virtual Reality (VR) and Augmented Reality (AR) data visualisation techniques for the analysis of radio astronomy data.

30 pages, 34 figures, Accepted for publication on MNRAS. 3D Virtual Reality view of the cloud here: http://hologhost.altervista.org/VR/index.html#

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