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21st of July 2016
Star formation within the central few hundred parsecs of the Milky Way
by Ashley Barnes (Liverpool John Moores University, UK)
The central few hundred parsecs of the Milky Way contains the majority of the Galaxy's dense molecular gas. The conditions within this region are extreme compared to those within the Galactic disc: the density, temperature, pressure, velocity dispersion, interstellar radiation field and cosmic ray ionisation rate are factors of a few to several orders of magnitude larger. However, it has been noted for several decades that despite harbouring this vast reservoir of dense gas, the Galactic Centre appears to be underproducing stars with respect to that in nearby star-forming regions. This work investigates potential explanations for this by studying the star formation rate within individual Galactic Centre gas clouds.

The map shown here is a portion of the Galactic Centre which contains several actively star-forming and quiescent gas clouds, which have been labeled. The red and blue indicate warm and cool gas, respectively, determined from Spitzer and Herschel space telescope observations. Overlaid is a top-down schematic diagram of the orbit as proposed by Kruijssen, Dale & Longmore (2015) for gas in the inner few hundred parsec of the Galactic Centre, and the relation of the observed clouds and this model. - The region is currently being observed with the Australia Telescope Compact Array (ATCA) as part of the "Survey of Water and Ammonia in the Galactic Center" (SWAG) project.

In agreement with the orbital model, we see a progression of star formation activity along the orbit. Star formation is in its early stages at the position of "the brick" molecular cloud, heavily embedded towards the Sgr B2 molecular cloud, and in its later stages towards the Sgr B1 HII region complex. Studying the progression of star formation within these clouds on pc scales we find agreement between the observed star formation rate to that predicted from the theoretical models. This is in stark contrast to the global scale star formation rate averaged over hundred parsec scales, which is orders of magnitude smaller than theoretically predicted.

We confirm that the low star formation rate when averaging over hundred parsec scales is due to the gas not being gravitationally-bound, despite its very high density. Conversely, the gas within the individual clouds on pc-scales is self-gravitating, explaining why, in contrast, it is forming stars at a rate consistent with predictions of theoretical models for star formation.

This work is presented as a poster at the IAU 322 Symposium.

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