EPoS Contribution
EPoS Contribution
The Critical Role of Galactic Dynamics in Regulating the Spatial Structure, Kinematics, and Star Formation Activity of Clouds in the Central Molecular Zone

Diederik Kruijssen
U Heidelberg, Heidelberg, DE
The Central Molecular Zone (the central ~500 pc of the Galaxy) is the most extreme star-forming environment in the Milky Way in terms of gas pressures, densities, temperatures, and dynamics. It acts as a critical archetype for developing star formation theories beyond the comfort zone of the solar neighbourhood. I will present a set of numerical simulations of molecular clouds orbiting on the 100-pc stream in the CMZ, with the goal of characterising their morphological and kinematic evolution in response to the external gravitational potential and their eccentric orbital motion. This is the first time that simulations capture the evolution of single clouds in a strong and plausibly dominant background potential. We find that the evolution of the clouds is closely coupled to the orbital dynamics and their arrival on the 100-pc stream marks a transformative event in their lifecycle. The clouds' sizes, aspect ratios, position angles, filamentary structure, column densities, velocity dispersions, line-of-sight velocity gradients, angular momenta, and overall kinematic complexity are controlled by the background potential and their passage through the orbit's pericentre. We compare these predictions of our simulations to observations of clouds on the Galactic Centre 'dust ridge' and find that the inclusion of galactic dynamics naturally reproduces a surprisingly wide array of key observed morphological and kinematic features. We argue that the accretion of gas clouds onto the central regions of galaxies, where the rotation curve turns over and the tidal field becomes fully compressive, is likely to lead to their collapse and associated star formation. During their subsequent evolution, the clouds are shaped by high levels of shear, as well as tidal and geometric deformation. This can generate an evolutionary progression of cloud collapse with a common zero point, which either marks the time of accretion or of the most recent pericentre passage, depending on the time of accretion. Together, these processes may naturally give rise to the synchronised starbursts observed in numerous (extra)galactic nuclei.
Caption: Combined column density maps of the simulations at several different snapshots, chosen to match the positions of observed clouds on the CMZ "dust ridge". The orbit of the clouds is shown as the light grey line, with the segment covered by the simulations shown in a brighter shade and arrows indicating the direction of motion. Top panel: top-down projection. Middle panel: plane-of-sky projection. For comparison, the observed column density map of the dense gas traced by cold dust (from HiGAL; Battersby et al. in prep.) is shown by contours at levels indicated by the black lines in the colour bar. This figure shows that the main morphological and kinematic features of the observed dust ridge clouds can be reproduced by simulating their dynamical evolution in the gravitational potential of the CMZ.
J. Dale, Hertfordshire, UK
S. Longmore, LJMU, UK
Key publication

Suggested Session: Molecular clouds