38) Linking Galactic and extragalactic stellar populations with nuclear star clusters

Abstract: Current instruments and spectral analysis programs are now able to decompose the integrated spectrum of a stellar system into distributions of ages and metallicities. The reliability of these methods have rarely been tested on nearby systems with resolved stellar ages and metallicities. I will compare the age-metallicity distribution of M54, the nucleus of the Sagittarius dSph galaxy, recovered from individual ages and metallicities from its resolved stars and from full spectral fitting its integrated spectrum. Both measurements were derived from the same MUSE dataset covering M54 out to 2.5 effective radii. The resulting age-metallicity distribution from both analyses reveal complex stellar populations, with consistent old (>8Gyr), metal-poor (-1.5dex) and young (1-2Gyr), metal-rich (0.00-0.25dex) components. I will also discuss the robustness of the age-metallicity recovery from integrated spectra. By co-adding individual stars to create M54's integrated spectrum, I will show that the recovered age-metallicity distribution is insensitive to the magnitude limit of the stars or the contribution of blue horizontal branch stars - even when including additional blue wavelength coverage from the WAGGS survey. However, the brightest stars can induce the spurious recovery of an old (>8 Gyr), metal-rich (+0.25 dex) stellar population. Derived stellar mass-to-light ratios from the integrated analysis decrease towards the center of M54 as the contribution of the young, metal-rich component increases - also in agreement with the resolved analysis. These findings provide strong evidence that complex stellar population distributions can be reliably recovered from integrated spectra of extragalactic systems.

Bio: I am a PhD student at the Max-Planck-Instiute for Astronomy in Heidelberg in the group of Nadine Neumayer. In my research I am mainly interested in developing new techniques that use stellar populations properties of galaxies or nuclear star clusters to learn about their mass assembly history. I especially focus on methods that recover distributions in ages and metallicities from integrated spectra, which I then apply to MUSE observations and cosmological simulations such as EAGLE and TNG.