The SkyMapper-Gaia RVS view of the Sausage — an investigation of the metallicity and mass of the Milky Way’s last major merger. (arXiv:2003.11039v1 [astro-ph.GA])

The SkyMapper-Gaia RVS view of the Sausage — an investigation of the metallicity and mass of the Milky Way’s last major merger. (arXiv:2003.11039v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Feuillet_D/0/1/0/all/0/1">Diane K Feuillet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Feltzing_S/0/1/0/all/0/1">Sofia Feltzing</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sahlholdt_C/0/1/0/all/0/1">Christian Sahlholdt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Casagrande_L/0/1/0/all/0/1">Luca Casagrande</a>

We characterize the Gaia-Sausage kinematic structure recently discovered in
the Galactic halo using photometric metallicities from the SkyMapper survey,
and kinematics from Gaia radial velocities measurements. By examining the
metallicity distribution functions (MDFs) of stars binned in kinematic/action
spaces, we find that the $sqrt{J_R}$ vs $L_z$ space allows for the cleanest
selection of Sausage stars with minimal contamination from disc or halo stars
formed in situ or in other past mergers. Stars with $30 leq sqrt{J_R} leq
50$ (kpc km s$^{-1})^{1/2}$ and $-500 leq L_z leq 500$ kpc km s$^{-1}$ have a
narrow MDF centered at [Fe/H] $= -1.17$ dex with a dispersion of 0.34 dex. This
[Fe/H] estimate is more metal-rich than literature estimates by $0.1-0.3$ dex.
Based on the MDFs, we find that selection of Sausage stars in other
kinematic/action spaces without additional population information leads to
contaminated samples. The clean Sausage sample selected according to our
criteria is {it slightly} retrograde and lies along the blue sequence of the
high $V_T$ halo CMD dual sequence. Using a galaxy mass-metallicity relation
derived from cosmological simulations and assuming a mean stellar age of 10 Gyr
we estimate the mass of the Sausage progenitor satellite to be $10^{8.85-9.85}$
M$_{odot}$, which is consistent with literature estimates based on disc
dynamic and simulations. Additional information on detailed abundances and ages
would be needed for a more sophisticated selection of purely Sausage stars.

We characterize the Gaia-Sausage kinematic structure recently discovered in
the Galactic halo using photometric metallicities from the SkyMapper survey,
and kinematics from Gaia radial velocities measurements. By examining the
metallicity distribution functions (MDFs) of stars binned in kinematic/action
spaces, we find that the $sqrt{J_R}$ vs $L_z$ space allows for the cleanest
selection of Sausage stars with minimal contamination from disc or halo stars
formed in situ or in other past mergers. Stars with $30 leq sqrt{J_R} leq
50$ (kpc km s$^{-1})^{1/2}$ and $-500 leq L_z leq 500$ kpc km s$^{-1}$ have a
narrow MDF centered at [Fe/H] $= -1.17$ dex with a dispersion of 0.34 dex. This
[Fe/H] estimate is more metal-rich than literature estimates by $0.1-0.3$ dex.
Based on the MDFs, we find that selection of Sausage stars in other
kinematic/action spaces without additional population information leads to
contaminated samples. The clean Sausage sample selected according to our
criteria is {it slightly} retrograde and lies along the blue sequence of the
high $V_T$ halo CMD dual sequence. Using a galaxy mass-metallicity relation
derived from cosmological simulations and assuming a mean stellar age of 10 Gyr
we estimate the mass of the Sausage progenitor satellite to be $10^{8.85-9.85}$
M$_{odot}$, which is consistent with literature estimates based on disc
dynamic and simulations. Additional information on detailed abundances and ages
would be needed for a more sophisticated selection of purely Sausage stars.

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