Jacob Kosowski, who is a PhD student at the University of Helsinki.

Title:

Using Modified Hausdorff Distances to Identify X-ray/Optical Galaxy Groups

Abstract:

Identification of X-ray and CMB sources as galaxy clusters is a prerequisite for cluster cosmology. Low redshift groups and clusters of galaxies were the first to be discovered, yet their identification suffer from projection effects, as they occupy large areas of the sky. Necessary limitations to maintain the purity of the sample can affect the completeness of the identification. The current approach to focus on the optical and X-ray centers as a form of matching is subject to multiple issues, in particular bright optical outliers.

We present a method to match X-ray emissions and optical galaxy groups that takes into account the large-scale structures of both components. Applying this method on RASS and SDSS data produces a catalog of galaxy groups of high purity and completeness, in particular for groups with velocity dispersion below 300 km/s. Several of these groups have large distances between X-ray and optical centers, but we are still able to provide a confident match using the large-scale distributions of group members and X-ray emissions. Preliminary results from applying this method to eRASS data are promising.