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Three-quarters of the Sky, up to 120 kpc: Mapping the Galactic Halo in 3D with PS1 RR Lyrae Stars

Friday, January 27, 2017
2:00 PM - 3:00 PM
Location: Cahill 370
Branimir Sesar, Senior Postdoctoral Researcher, Max Planck Institute for Astronomy (MPIA)

If we could map the Galactic halo structure, substructure, and kinematics with high precision and over a large volume, we could search for the faintest Milky Way satellites, measure the properties of the Galactic dark matter halo, and through comparisons with state-of-the-art simulations, constrain the theory of galaxy formation.

I will present one such map of the Galactic halo, traced using a sample of 45,000 RR Lyrae stars selected from the Pan-STARRS1 (PS1) survey, that covers three-quarters of the sky up to 120 kpc of the Sun. I will describe how I used machine learning to select the above sample from a large, but sparse multiband PS1 dataset, and how I plan to use similar datasets, such as those produced by LSST and ZTF, to study the far side of the Galaxy.

As the first preliminary result, I will present the deepest and widest view of the Sagittarius tidal stream, and demonstrate that the so-called Gemini stream (Drake et al. 2013), is simply a distant part of the Sagittarius stream.

For more information, please phone 626-395-6608 or email or visit

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