‘The Brick’ is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016. (arXiv:1902.02793v1 [astro-ph.GA])

‘The Brick’ is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016. (arXiv:1902.02793v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Henshaw_J/0/1/0/all/0/1">J. D. Henshaw</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ginsburg_A/0/1/0/all/0/1">A. Ginsburg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haworth_T/0/1/0/all/0/1">T. J. Haworth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Longmore_S/0/1/0/all/0/1">S. N. Longmore</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kruijssen_J/0/1/0/all/0/1">J. M. D. Kruijssen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mills_E/0/1/0/all/0/1">E. A. C. Mills</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sokolov_V/0/1/0/all/0/1">V. Sokolov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Walker_D/0/1/0/all/0/1">D. L. Walker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barnes_A/0/1/0/all/0/1">A. T. Barnes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Contreras_Y/0/1/0/all/0/1">Y. Contreras</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bally_J/0/1/0/all/0/1">J. Bally</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Battersby_C/0/1/0/all/0/1">C. Battersby</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beuther_H/0/1/0/all/0/1">H. Beuther</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Butterfield_N/0/1/0/all/0/1">N. Butterfield</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dale_J/0/1/0/all/0/1">J. E. Dale</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henning_T/0/1/0/all/0/1">T. Henning</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jackson_J/0/1/0/all/0/1">J. M. Jackson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kauffmann_J/0/1/0/all/0/1">J. Kauffmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pillai_T/0/1/0/all/0/1">T. Pillai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ragan_S/0/1/0/all/0/1">S. Ragan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Riener_M/0/1/0/all/0/1">M. Riener</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_Q/0/1/0/all/0/1">Q. Zhang</a>

In this paper 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.
In this paper, we reanalyse Atacama Large Millimeter Array cycle 0 HNCO
$J=4(0,4)-3(0,3)$ data at 3 mm, using two new pieces of software which we make
available to the community. First, scousepy, a Python implementation of the
spectral line fitting algorithm scouse. Secondly, acorns (Agglomerative
Clustering for ORganising Nested Structures), a hierarchical n-dimensional
clustering algorithm designed for use with discrete spectroscopic data.
Together, these tools provide an unbiased measurement of the line of sight
velocity dispersion in this cloud, $sigma_{v_{los}, {rm 1D}}=4.4pm2.1$
kms$^{-1}$, which is somewhat larger than predicted by velocity dispersion-size
relations for the Central Molecular Zone (CMZ). The dispersion of centroid
velocities in the plane of the sky are comparable, yielding $sigma_{v_{los},
{rm 1D}}/sigma_{v_{pos}, {rm 1D}}sim1.2pm0.3$. This isotropy may indicate
that the line-of-sight extent of the cloud is approximately equivalent to that
in the plane of the sky. Combining our kinematic decomposition with radiative
transfer modelling we conclude that G0.253+0.016 is not a single, coherent, and
centrally-condensed molecular cloud; ‘the Brick’ is not a emph{brick}.
Instead, G0.253+0.016 is a dynamically complex and hierarchically-structured
molecular cloud whose morphology is consistent with the influence of the
orbital dynamics and shear in the CMZ.

In this paper 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.
In this paper, we reanalyse Atacama Large Millimeter Array cycle 0 HNCO
$J=4(0,4)-3(0,3)$ data at 3 mm, using two new pieces of software which we make
available to the community. First, scousepy, a Python implementation of the
spectral line fitting algorithm scouse. Secondly, acorns (Agglomerative
Clustering for ORganising Nested Structures), a hierarchical n-dimensional
clustering algorithm designed for use with discrete spectroscopic data.
Together, these tools provide an unbiased measurement of the line of sight
velocity dispersion in this cloud, $sigma_{v_{los}, {rm 1D}}=4.4pm2.1$
kms$^{-1}$, which is somewhat larger than predicted by velocity dispersion-size
relations for the Central Molecular Zone (CMZ). The dispersion of centroid
velocities in the plane of the sky are comparable, yielding $sigma_{v_{los},
{rm 1D}}/sigma_{v_{pos}, {rm 1D}}sim1.2pm0.3$. This isotropy may indicate
that the line-of-sight extent of the cloud is approximately equivalent to that
in the plane of the sky. Combining our kinematic decomposition with radiative
transfer modelling we conclude that G0.253+0.016 is not a single, coherent, and
centrally-condensed molecular cloud; ‘the Brick’ is not a emph{brick}.
Instead, G0.253+0.016 is a dynamically complex and hierarchically-structured
molecular cloud whose morphology is consistent with the influence of the
orbital dynamics and shear in the CMZ.

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