The Chemo-dynamical Origin of the Typhon Outer Halo Stellar Stream

• Grant number: 24/22429-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2025
• End date: December 31, 2025
• Field of knowledge: Physical Sciences and Mathematics - Astronomy - Stellar Astrophysics
• Principal Investigator: Silvia Cristina Fernandes Rossi
• Grantee: João Vitor Nogueira dos Santos
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 20/15245-2 - The multi-object spectrograph (MOSAIC) for the extremely large telescope: spectroscopy of stellar populations in the milky way and external galaxies, AP.ESP

Abstract

In lambda cold dark matter cosmology, the halos of massive galaxies are assembled through successiveaccretion of smaller systems. Hence, identifying the debris of tidally disrupted dwarf galaxies in theMilky Way's halo is crucial to achieve a census of merging events that happened throughout thehistory of our Galaxy, a major goal in Galactic Archaeology. In this project, we will investigate themetallicity distribution function of Typhon stellar stream, just recently discovered in data from theGaia mission. The Typhon stream can reach orbital apocenters of >100 kpc from the Galactic center,hence providing a glimpse of stellar populations lurking in the outermost regions of the Milky Way.However, several Typhon members can be found near the solar vicinity (within 4 kpc) close to theirpericenters, so we can study the properties of the outer halo with nearby stars that are amenableto spectroscopy. Unfortunately, few members are currently known with metallicity measurements,impeding us from determining whether Typhon is really a tidally disrupted dwarf galaxy or just aglobular cluster. The goal of this project is to identify additional members of Typhon outer halo stellarstream with publicly-available spectroscopic observations in large-survey data through kinematics. Wewill incorporate realistic metallicity uncertainties to fit Gaussian metallicity distributions for Typhonand measure associated dispersions. In the case of a large resolved metallicity dispersion, Typhonmust be an accreted dwarf galaxy. On the other hand, if the metallicity dispersion is unresolved,Typhon will be classified as a disrupted globular cluster. Given the somewhat high mean metallicityof Typhon ([Fe/H] of the order of -1.4dex), its progenitor is expected to be relatively massive, indicating that thisstellar stream could represent a major building block of the Milky Way.