Central Molecular Zone

The "Brick" is not a brick

In this publication, we provide a comprehensive description of the internal dynamics of G0.253+0.016 (a.k.a. 'the Brick'); one of the most massive and dense molecular clouds in the Galaxy to lack signatures of widespread star formation. As a potential host to a future generation of high-mass stars, understanding largely quiescent molecular clouds like G0.253+0.016 is of critical importance. Using data obtained with the Atacama Large Millimeter Array located in the Atacama desert in Chile, we found that, contrary to what was previously thought, G0.253+0.016 is not a single, coherent, and centrally-condensed molecular cloud; 'the Brick' is not a brick. Instead, G0.253+0.016 harbours a complex network of nested structure. The cloud's structure and dynamics are consistent with the influence of the orbital dynamics and shear in the CMZ.

J. D. Henshaw et al., 2019, MNRAS, 485, 2457

You can obtain the arxiv version of the text here.

The growth of molecular clouds

Star formation within the CMZ is intimately linked to the orbital dynamics of the gas. Recent models suggest that star formation within some of the most massive clouds in this region may follow an evolutionary time sequence. Given that these clouds, e.g. the Brick (see above), are the most likely precursors to a generation of massive stars and extreme star clusters, this scenario would have profound implications for constraining the time-evolution of star formation.

In 2016, we began a search for the initial conditions of these massive protocluster clouds. We identified a series of clouds with masses around 10000x the mass of the sun. They show no obvious signatures of active star formation and are regularly spaced with a separation of ~10 parsecs. In addition, we identified an intriguing velocity pattern in the molecular gas associated with these clouds. The gas kinematics show a clear sinusoidal oscillatory pattern, the wavelength of which is around ~20parsecs.

We suggested that the clouds may have formed as the gas within the CMZ has become gravitationally unstable and that the oscillatory pattern may be a signature of gas accretion towards the clouds. This indicates that the clouds are still in an early phase of their evolution and continue to gather mass from their surroundings. If confirmed, these clouds may represent precursors to some of the most massive molecular clouds in the Galaxy.

J. D. Henshaw, S. N. Longmore, & J. M. D. Kruijssen, 2016, MNRAS, 463, L22

You can obtain the arxiv version of the text here.

The orbital dynamics of the Central Molecular Zone

In this publication, we investigate the kinematics of dense gas in the central ∼250 pc of the Galaxy. Through the development of SCOUSE, we were able to accurately determine the {l, b, vLSR} distribution of Central Molecular Zone (CMZ) gas, finding it to be asymmetric about Sgr A* in both position and velocity, consistent with previous works. The gas is distributed throughout several "streams", with projected lengths ∼100-250 pc. We link the streams to individual clouds and sub-regions, including Sgr C, the 20 and 50 km s-1 clouds, the dust ridge, and Sgr B2, and discuss their structure and dynamics. We compare and contrast three theoretical geometries describing the 3D structure of the CMZ: (I) two spiral arms; (II) a closed elliptical orbit; (III) an open stream. While two spiral arms and an open stream qualitatively reproduce the gas distribution, the most recent parametrisation of a closed elliptical orbit does not. Finally, we discuss how proper motion measurements of masers can distinguish between these geometries, and suggest that this effort should be focused on the 20 km s-1 and 50 km s-1 clouds and Sgr C.

J. D. Henshaw et al., 2016, MNRAS, 457, 2675

You can obtain the arxiv version of the text here.