'The Brick' is not a brick: A comprehensive study of the structure and
  dynamics of the Central Molecular Zone cloud G0.253+0.016
  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, $\sigma_{v_{los}, {\rm 1D}}=4.4\pm2.1$
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 $\sigma_{v_{los},
{\rm 1D}}/\sigma_{v_{pos}, {\rm 1D}}\sim1.2\pm0.3$. 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.
