Substructures in the Milky Way halo in the era of large scale spectroscopic surveys

Thursday, 27 April 2023 1 p.m. — 2 p.m. MST

AURA Lecture Hall

NOIRLab South Colloquia
Eduardo Balbinot (Kapteyn Institute at the University of Groningen)

Galaxies like the Milky Way are one of the end products of a hierarchical formation process - predicted by Cold Dark Matter (CDM) - and the vast number of smaller satellites and substructures (stellar streams and clouds) observed in the Local Group today are the relics of its formation history. Surprisingly, despite making up most of the mass in the Universe, the nature of Dark Matter (DM) remains elusive. On large scales, its observed distribution is consistent with a cold, collisionless particle that lies beyond the standard model of particles. Yet on smaller scales there has been a longstanding tension between theoretical models and observations. In particular, the prediction of a large population of pure DM subhalos. Thanks to Gaia, we know that the Galaxy halo is almost exclusively comprised of a handful of accretion events. Also inhabiting the MW halo are cold stellar streams, formed through the dissolution of dwarf galaxies or globular clusters. These are observed as thin bands of stars - that roughly follow a single orbit - in the Galaxy halo, a region expected to be swarming with DM subhalos. Streams are fragile, once the stars leave the progenitor, their trajectories are only subject to the MW potential and small perturbations can drastically change their orbits, making them perfect probes for the presence of pure DM subhalos. In this talk I will give an overview of the new accretion events and streams identified in Gaia, as well as discuss recent results on the modelling of streams and their gaps/perturbations in the presence of massive baryonic perturbers. I will discuss the role multi-object spectrographs, such as WEAVE, DESI, and 4MOST, will play in mapping the accretion history of the Galaxy and measuring perturbations to stellar streams by DM subhalos. Upcoming surveys, such as LSST, will push the field of Galactic Archaeology to the outskirts of the Galaxy and to the Local Group. I will briefly discuss its impact and synergies with present and upcoming facilities such as (E-ELT, TMT, and MSE).