Oral Abstract

Oral Contribution (O0.8) Akshara Viswanathan (Kapteyn Astronomical Institute, University of Groningen)

A unique view of the metallicity structure of the Milky Way halo

The Milky Way stellar halo is diffuse and full of chemical and dynamical substructures that relate to the complex history of our galaxy in the distant past. Starting from a list of halo main sequence stars in Gaia eDR3 selected using the reduced proper motion method, we infer the metallicity information from the very-metallicity sensitive Pristine survey. This results in a set of ~0.76M stars with reliable photometric metallicities as well as distance estimates – the typical distance uncertainty for these stars is 7% and the heliocentric distance ranges between 0 and 21 kpc with a mean of 7 kpc, thereby probing much further out than would be possible using reliable Gaia parallaxes. From the distribution of binned velocity moments in the sky, several stream-like features stand out at higher distances in this sample.
We study the metallicity structure of the halo in different distance slices and map out the metal-poor Milky Way halo across various lines of sight. Our results confirm an overall metallicity distribution function (MDF) of the local halo population with a peak at [Fe/H]=-1.6, consistent with literature results. We trace a probable extension of Phlegethon stream and another sub-structure that crosses Phlegethon from the [Fe/H]<-2 metallicity space in the sky. We use our results to better constrain the contributions of (kicked up) thick disk stars at different scale heights in this kinematically selected halo sample. By combining these two powerful surveys, we thus get a better view of some of the most intricate parts of our Galaxy.