The geometry of the gas surrounding the Central Molecular Zone: on the origin of localised molecular clouds with extreme velocity dispersions. (arXiv:1906.10129v1 [astro-ph.GA])

The geometry of the gas surrounding the Central Molecular Zone: on the origin of localised molecular clouds with extreme velocity dispersions. (arXiv:1906.10129v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Sormani_M/0/1/0/all/0/1">Mattia C. Sormani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tress_R/0/1/0/all/0/1">Robin G. Tress</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Glover_S/0/1/0/all/0/1">Simon C.O. Glover</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Klessen_R/0/1/0/all/0/1">Ralf S. Klessen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barnes_A/0/1/0/all/0/1">Ashley T. Barnes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Battersby_C/0/1/0/all/0/1">Cara D. Battersby</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clark_P/0/1/0/all/0/1">Paul C. Clark</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hatchfield_H/0/1/0/all/0/1">H Perry Hatchfield</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_R/0/1/0/all/0/1">Rowan J. Smith</a>

Observations of molecular gas near the Galactic centre ($| l | < 10^circ$, $| b | < 1^circ$) reveal the presence of a distinct population of enigmatic compact clouds which are characterised by extreme velocity dispersions ($Delta v > 100, rm km/s$). These Extended Velocity Features (EVFs) are very
prominent in the datacubes and dominate the kinematics of molecular gas just
outside the Central Molecular Zone (CMZ). The prototypical example of such a
cloud is Bania Clump 2. We show that similar features are naturally produced in
simulations of gas flow in a realistic barred potential. We analyse the
structure of the features obtained in the simulations and use this to interpret
the observations. We find that the features arise from collisions between
material that has been infalling rapidly along the dust lanes of the Milky Way
bar and material that belongs to one of the following two categories: (i)
material that has `overshot’ after falling down the dust lanes on the opposite
side; (ii) material which is part of the CMZ. Both types of collisions involve
gas with large differences in the line-of-sight velocities, which is what
produces the observed extreme velocity dispersions. Examples of both categories
can be identified in the observations. If our interpretation is correct, we are
directly witnessing (a) collisions of clouds with relative speeds of $sim
200, rm km/s$ and (b) the process of accretion of fresh gas onto the CMZ.

Observations of molecular gas near the Galactic centre ($| l | < 10^circ$,
$| b | < 1^circ$) reveal the presence of a distinct population of enigmatic
compact clouds which are characterised by extreme velocity dispersions ($Delta
v > 100, rm km/s$). These Extended Velocity Features (EVFs) are very
prominent in the datacubes and dominate the kinematics of molecular gas just
outside the Central Molecular Zone (CMZ). The prototypical example of such a
cloud is Bania Clump 2. We show that similar features are naturally produced in
simulations of gas flow in a realistic barred potential. We analyse the
structure of the features obtained in the simulations and use this to interpret
the observations. We find that the features arise from collisions between
material that has been infalling rapidly along the dust lanes of the Milky Way
bar and material that belongs to one of the following two categories: (i)
material that has `overshot’ after falling down the dust lanes on the opposite
side; (ii) material which is part of the CMZ. Both types of collisions involve
gas with large differences in the line-of-sight velocities, which is what
produces the observed extreme velocity dispersions. Examples of both categories
can be identified in the observations. If our interpretation is correct, we are
directly witnessing (a) collisions of clouds with relative speeds of $sim
200, rm km/s$ and (b) the process of accretion of fresh gas onto the CMZ.

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