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.

‘The Brick’ is not a<i>brick</i>: a comprehensive study of the structure and dynamics of the central molecular zone cloud G0.253+0.016

Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

National Radio Astronomy Observatory, 1003 Lopezville Rd., Socorro, NM 87801, USA

Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK

Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF, UK

Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg, Germany

Physics Department, Brandeis University, 415 South Street, Waltham, MA 02453, USA

Max Planck Institute for Extraterrestrial Physics, Gießenbachstraße 1, D-85748 Garching bei München, Germany

Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile

National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Argelander Institute for Astronomy, University of Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands

Center for Astrophysics and Space Astronomy, Astrophysical and Planetary Sciences Department, University of Colorado, Boulder, CO 80309, USA

National Radio Astronomy Observatory, PO Box 2, Green Bank, WV 24944, USA

Department of Physics, University of Connecticut, Storrs, CT 06269, USA

Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK

School of Mathematical and Physical Sciences, University of Newcastle, University Drive, Callaghan NSW 2308, Australia

Hay Stack Observatory, Massachusetts Institute of Technology, 99 Millstone Road, Westford, MA 01886, USA

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53212 Bonn, Germany

Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff CF24 3AA, UK

Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

‘The Brick’ is not abrick: a comprehensive study of the structure and dynamics of the central molecular zone cloud G0.253+0.016