Heidelberg Joint Astronomical Colloquium

Speaker Rolf Kudritzki
Title Stellar spectroscopy unleashed–ELTs and red supergiants in the Coma cluster

The determination of the chemical composition and distances of galaxies is crucial for constraining the theory of galaxy formation and evolution in a dark energy and cold dark matter dominated universe. However, the standard techniques to obtain information about the chemical composition and distances of star forming galaxies are subject to large systematic uncertainties which are poorly understood.

As an alternative, I introduce a new method, which will use low resolution J-band spectroscopy of individual red supergiant stars (RSGs) in distant galaxies. Using Mauna Kea IRTF SpeX low resolution spectra of Milky Way RSGs and MARCS model atmospheres we have demonstrated that our analysis method allows individual metallicities and alpha/Fe ratios to be determined with an accuracy of about 0.1 dex (Davies, Kudritzki, Figer, 2010, MNRAS 407, 1203). The extension of the method to star forming galaxies beyond the Local Group with MOS devices at large telescopes such as MOSFIRE/Keck and KMOS/VLT is straightforward.

This new method will gain tremendous momentum with the next generation of ELTs and AO supported MOS instruments like IRMS at the TMT and EAGLE at the E-ELT, since the limiting magnitude in the diffraction limit case increases with the fourth power of the telescope diameter. We have shown that we can reach individual RSGs in galaxies as distant as the Coma Cluster (Evans, Davies, Kudritzki et al., 2011, A&A 527, 50).

I will also discuss the potential of observing the integrated light of Super Star Clusters (SSCs). The J-band light of these objects is entirely dominated by RSGs as soon as the cluster age is larger than 8 Myr (Gazak, Kudritzki, Davies, 2011, in prep.). This allows for the determination of accurate detailed chemical composition by simple population synthesis techniques. Because of the enormous brightness of SSCs in the J-band an enormous volume of the local universe can be studied in this way.