Antlia2’s role in driving the ripples in the outer gas disk of the Galaxy. (arXiv:1906.04203v1 [astro-ph.GA])

Antlia2’s role in driving the ripples in the outer gas disk of the Galaxy. (arXiv:1906.04203v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Chakrabarti_S/0/1/0/all/0/1">Sukanya Chakrabarti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chang_P/0/1/0/all/0/1">Philip Chang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Price_Whelan_A/0/1/0/all/0/1">Adrian Price-Whelan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Read_J/0/1/0/all/0/1">Justin Read</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blitz_L/0/1/0/all/0/1">Leo Blitz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hernquist_L/0/1/0/all/0/1">Lars Hernquist</a>

We employ the observed Gaia proper motions of the newly discovered Antlia 2
dwarf galaxy to calculate its orbital distribution in the cosmologically recent
past. Using these observationally motivated orbits, we calculate the effect of
the Antlia 2 dwarf galaxy on the outer HI disk of the Milky Way, using both
test particle and Smoothed Particle Hydrodynamics simulations. We find that
orbits with low pericenters, $sim$ 10 kpc, produce disturbances that match the
observed outer HI disk perturbations. We also show that the Sagittarius dwarf
galaxy interaction does not match the observed perturbations in the outer gas
disk. Thus, we argue that Antlia 2 is the likely driver of the observed large
perturbations in the outer gas disk of the Galaxy. The current location of the
Antlia 2 dwarf galaxy closely matches that predicted by an earlier dynamical
analysis (Chakrabarti & Blitz 2009) of the dwarf that drove ripples in the
outer Galaxy, and, in particular, its orbit is nearly coplanar to the Galactic
disk. If the Antlia 2 dwarf galaxy is responsible for the perturbations in the
outer Galactic disk, it would have a specific range of proper motions that we
predict here; this can be tested soon with Gaia DR-3 and Gaia DR-4 data.

We employ the observed Gaia proper motions of the newly discovered Antlia 2
dwarf galaxy to calculate its orbital distribution in the cosmologically recent
past. Using these observationally motivated orbits, we calculate the effect of
the Antlia 2 dwarf galaxy on the outer HI disk of the Milky Way, using both
test particle and Smoothed Particle Hydrodynamics simulations. We find that
orbits with low pericenters, $sim$ 10 kpc, produce disturbances that match the
observed outer HI disk perturbations. We also show that the Sagittarius dwarf
galaxy interaction does not match the observed perturbations in the outer gas
disk. Thus, we argue that Antlia 2 is the likely driver of the observed large
perturbations in the outer gas disk of the Galaxy. The current location of the
Antlia 2 dwarf galaxy closely matches that predicted by an earlier dynamical
analysis (Chakrabarti & Blitz 2009) of the dwarf that drove ripples in the
outer Galaxy, and, in particular, its orbit is nearly coplanar to the Galactic
disk. If the Antlia 2 dwarf galaxy is responsible for the perturbations in the
outer Galactic disk, it would have a specific range of proper motions that we
predict here; this can be tested soon with Gaia DR-3 and Gaia DR-4 data.

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