VIRUS eROSITA Galaxy Cluster spectroscopic follow-up
Fabian Balzer (1), Maximilian Fabricius (1), Ralf Bender (1), Esra Bulbul (1), Gary Hill (2)
(1) Max-Planck-Institut für extraterrestrische Physik, (2) McDonald Observatory, University of Texas Austin
The VIRUS eROSITA follow-up program aims to provide optical follow-up spectroscopy for galaxies in ~200 galaxy clusters selected by the eROMaPPer cluster finding algorithm (Kluge et al. in prep, see also Rykoff et al. 2014 for the preceding redMaPPer algorithm) in a redshift range of 0.1 < z < 0.4. The blind integral field spectroscopy obtained via observations with the VIRUS instrument at the Hobby-Eberly Telescope at McDonald observatory enables not only to conduct the analysis of the cluster's confirmed member galaxy spectra, but also to obtain spectra of further associated objects such as late-type galaxies missed by the red-sequence-based membership assignment algorithm. The availability of individual member galaxy redshifts additionally allows for dynamical studies and a comparison of optical and X-ray properties for each of the observed clusters. During the first year of observations, 99 clusters were observed with a 1/4 fill factor due to the nature of the VIRUS instrument, and a data analysis pipeline was devised to obtain the redshifts and velocity dispersions of the clusters, making use of the more than 100,000 individual IFU fibre spectra of each observation. So far, the program yielded 931 novel spectroscopic redshifts of galaxies associated with clusters, and velocity dispersions for 39 of those. I aim to present the data analysis pipeline and future prospects.