Title：Using stellar populations from simulations and observations to measure past merger events in external galaxies

Speaker:Alina Boecker (University of Vienna)

Time：3:00 pm Sep. 18th (Thursday)

Tencent Meeting：46822606747 password: 6360

Location: Lecture Hall, 3rd floor

Abstract：

Thanks to Gaia and large spectroscopic surveys we now understand the past merger history of the Milky Way by examining the properties of its individual stars. For statistical samples of external galaxies however, integrated spectra are necessary to decode their stellar populations, which act as a fossil record of their assembly history. A tell-tale sign of past accretion events are stars that do not follow the chemical enrichment of the main progenitor galaxy, meaning that these stars are usually more metal-poor at fixed age than the in-situ stars. To measure these signatures, we need to extract the full 2D age-metallicity distribution from single integrated spectra, which is a difficult task due to the vast and degenerate parameter space. Additionally, spectroscopic observations typically only cover the central regions of galaxies, which are thought to be dominated by stars born in-situ. To overcome these, and more, challenges, I will talk about the crucial synergy between simulations and observations to build towards a methodology of recovering a galaxy’s individual merger history. Specifically, I will focus on the cosmological, hydrodynamical simulation IllustrisTNG, observations from SDSS and full spectral fitting methods to show that 1) current techniques can indeed extract information about the age-metallicity distribution from integrated spectra, 2) ex-situ stars do reside in the centers of galaxies while being identifiable as the oldest, most-metal poor and alpha-enhanced population, and 3) empirical chemical evolution templates allow us to recover the mass function of accreted satellite galaxies. Lastly, I will address current limitations, which are mainly related to stellar population modelling techniques as well as the subgrid physics implemented in cosmological simulation, as well as future directions to improve upon them. Still, together with the team efforts of simulators, observers and stellar population modelers we are now approaching an era where it will be possible to measure past merger events of thousands of individual galaxies. Perfecting these techniques now will prepare us for upcoming spectroscopic surveys at higher redshifts to fully understand the significance of merger events in the formation and evolution of galaxies across cosmic time.

CV：

Dr. Alina Boecker

2018-2022: PhD at the Max-Planck-Institute for Astronomy in Heidelberg, Germany (Research Group of Nadine Neumayer)

2022-2023: PostDoc at the Instituto de Astrofísica de Canarias in Tenerife, Spain (Research Group of Ignacio Martín-Navarro)

2024-Now: Fellow at the University of Vienna, Austria (Research Group of Glenn van de Ven)