Speaker: Songting Li

 

Abstract:

Our Milky Way (MW) Galaxy is an ideal laboratory to test the physics of galaxy formation and the underlying cosmology, because individual stars in the MW can be resolved by the observers. Various types of information can be extracted from the phase-space distribution of individual stars in the MW, which enables us to probe the spatial and kinematical structures of the MW disk, bulge, and halo, to infer the assembly history of the MW (galactic archaeology), and construct dynamical models to constrain the dark matter distribution around our MW. Among the 6-dimensional phase-space information, distances are the most essential. Our goal is to provide precise distance measurements for stars observed by DESI, not just limited to RRLyrae and BHBs. Since stellar spectra contain the physical information of the star (e.g. the surface gravity, effective temperature and [Fe/H] abundance), we can map the spectra to intrinsic luminosity of stars and get the distance estimates. 

 

In this talk we will present our current work of distance measurement for DESI Year-1 and Year-3 data, by training a feed-forward Neural Network (NN) with Gaia parallaxes. The median distance uncertainty of giants and main sequence stars in DESI Year-3 observation is 11 % and 8 % respectively. By combining those distance measurements with Gaia proper motion measurements, we aim to further measure the spatial distribution (including the shape, orientation and density profile of stellar halo) and the velocity distribution of MW stellar halo (including the velocity dispersion, velocity anisotropy and tiny rotation of stellar halo). We found that the MW stellar halo is roughly tilted oblate with the density profile obeys a double-power law. With the increase of distance, the stellar halo becomes more spherical and more tilted. Furthermore, we found a tiny rotation signal of stellar halo with the rotation velocity around -20 km/s.

Bio: 

I got my bachelor degree from Wuhan University. Currently I am a second year PhD student in DoA SJTU. I mainly work on stellar parameter measurements and Milky Way science in the research group of Wenting Wang and Jiaxin Han. I work and contribute actively in the DESI Milky Way Survey working group. 

 

PS: The talk will be given in Chinese.