Stellar Populations in Galaxies

One of the most interesting problems in modern astrophysics is to understand how galaxies form and evolve. Chemical composition of stars tell us about the formation history of their parent populations, from star clusters to galaxies. 

Galactic Archeology

We are interested in different aspectrs of observational galactic chemo-dynamics, including nucleosynthesis of even- and odd-Z elements,  abundance gradients in the Milky Way and its satellities, Galactic archeology and the structure of the Milky Way disk.

In the analysis of the data from the Gaia-ESO survey, we have shown that the age-metallicity relation of stars in the Milky Way disk has several pronounced features. Young stars with age less than 8 Gyr have a large range of  metallicities, consistent with no age-metallicity relation. However, no metal-rich star is observed with age above 9 Gyr. This casts doubt on the existence of such stars. 

We have also discovered that the distribution of element abundances with galactocentric radius depends on the age of the probed population. The gradient of Mg abundance steepens and becomes negative. In addition, we show that the inner disk is not only more αlpha-rich compared to the outer disk, but also older, as traced independently by the ages and Mg abundances of stars.

Abundance gradients in star-forming galaxies

As part of a large international collaboration, we are also involved in spectroscopic studies of extragalactic abundance gradients. We have developed a new unconventional method, NLTE infrared spectroscopy of red supergiants, which is used to determine elemental abundances, including Ti, Mg, Si, Fe, in the large spiral galaxies beyond the Local Group. 

Our approach is to measure strong absorption lines of chemical elements in the Infra-Red. The method greatly improves the accuracy of IR abundance diagnostics and opens new perspectives for the determination of chemical abundances in other galaxies.

In the long-term, there is also the possibility to extend our methods to galaxies beyond the Local Group through the spectroscopic analysis of unresolved stellar populations. Among the most interesting cases are the so-called Super Star Clusters, whose integrated light is dominated by RSGs already after few million years of evolution (Gazak et al. 2014). With the next generation of ELT-class telescopes, this opens up a new and challenging perspective to obtain the first detailed maps of chemical composition in star-forming galaxies out to distances of a few hundred Mpc (Evans et al. 2011). This will also enable accurate calibration of standard strong emission line methods on accurate metallicities of red supergiants.