IAUS379: Dynamical Masses of Local Group Galaxies

Like any other galaxy in the universe, evidence shows that the assembly of the Milky Way is irrefutably hierarchical. The Galactic halo in particular has a nonlinear structure with a vast number of cold stellar streams with complex morphologies that prove to be a powerful test for the nature and distribution of dark matter in the halo.

In this work, we select halo main sequence stars using Gaia DR3 proper motion and photometry information, the combination of which renders the reduced proper motion parameter. This parameter allows us to pick out high tangential velocity stars in halo orbits independent of the line-of-sight information. Our final catalogue consists of about 47 million halo main-sequence stars for which we can then determine precise photometric distances with typical uncertainties down to 7%. Our sample reaches out until ~20 kpc thereby probing much further out than would be possible using reliable Gaia parallaxes.

Binned velocity moments on the star map in the latitude, longitude and pseudo-azimuth directions pop up several known tidal streams in the local halo - particularly retrograde structures, due to the kinematic selection. The use of main-sequence stars, rather than brighter giants, allows us to trace low surface brightness counterparts, pushing the substructure searches to Gaia’s magnitude limits.

Here I will present the substructures found and characterise them in more detail, due to the added information in derived distances and existing metallicities as well as the higher sensitivity in low surface brightness features. For these streams, we resolve the gaps, wiggles, and density breaks reported in the literature more clearly. The faint signs of disequilibrium in the form of kinks and density variations in these thin streams will paint a more detailed picture of the existence and properties of the dark matter sub-haloes that perturb them and in turn, the mass distribution of our Galaxy.