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19th of April 2017
ATNF Colloquium
Tracing the Galactic bar through dense molecular cores with broad emission spectra
by Shaila Akhter (UNSW)
Abstract. Study of high-mass star formation help us to understand the evolution of our Galaxy, its surrounding ISM and shape of the Universe! Currently scientists do not know much how do these massive stars are born. A reason for this is they are rare and live for short time. So understanding the life cycle of a high mass star is a great challenge. We used NH3(1,1) data from the H2O Southern Galactic Plane Survey (HOPS) between -60 deg < l < -2.7 deg and 3.9 deg < l < 30 deg and |b| < 0.5 degrees to identify dense molecular regions/clumps of the Milky Way Galaxy that are likely to form high-mass stars. We identified ~ 500 such clumps - 14 of these clumps near the central molecular zone show broad emission spectral lines (with velocity widths between 19.8 and 47.6 km/s). We find that the same clumps exhibit broad emission spectra for other molecular lines - NH3(2,2), (3,3) and HC3N(3-2). Analysing these data we find that these clumps are grouped into three clusters of dense molecular cores centred at | l | = 5.5 deg and 10 deg. We name them 'Cluster-1', 'Cluster-2' (also known as 'Bania's Clump 1') and 'Cluster-3’. 'Cluster-1' and 'Cluster-2' are in inverse-symmetry in the l - b plane and the large velocity dispersion of each clump in these two clusters suggest that clusters 1 and 2 may be associated with the inner Galactic bar potential x-1 orbits. We find that 'Cluster-3' is likely to be undergoing high-mass star formation, as suggested by the presence of emission from H2O maser and radio recombination line (H69α) from HOPS.

The picture above is from Hou & Han (2014; their Figure 2) showing the longitude-velocity diagrams for the HII regions (upper panel), GMCs (middle panel), and 6.7 GHz methanol masers (lower panel) overlaid onto the 12CO(1-0) image from Dame et al. (2001).

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