A Multi-component Matched Filter Cluster Confirmation Tool for eROSITA:
  Initial Application to the RASS and DES-SV Datasets
  We describe a multi-component matched filter cluster confirmation tool (MCMF)
designed for the study of large X-ray source catalogs produced by the upcoming
X-ray all-sky survey mission eROSITA. We apply the method to confirm a sample
of 88 clusters with redshifts $0.05<z<0.8$ in the recently published 2RXS
catalog from the ROSAT all-sky survey (RASS) over the 208 deg$^2$ region
overlapped by the Dark Energy Survey (DES) science verification (DES-SV)
dataset. In our pilot study, we examine all X-ray sources, regardless of their
extent. Our method employs a multi-color red sequence (RS) algorithm that
incorporates the X-ray count rate and peak position in determining the region
of interest for followup and extracts the positionally and color weighted
optical richness $\lambda_{\mathrm{MCMF}}$ as a function of redshift for each
source. Peaks in the $\lambda_{\mathrm{MCMF}}$-redshift distribution are
identified and used to extract photometric redshifts, richness and
uncertainties. The significances of all optical counterparts are characterized
using the distribution of richnesses defined along random lines of sight. These
significances are used to extract cluster catalogs and to estimate the
contamination by random superpositions of unassociated optical systems. The
delivered photometric redshift accuracy is $\delta z / (1+z)=0.010$. We find a
well defined X-ray luminosity-$\lambda_{\mathrm{MCMF}}$ relation with an
intrinsic scatter of $\delta \ln(\lambda_\mathrm{MCMF}| L_\mathrm{x})=0.21$.
Matching our catalog with the DES-SV redMaPPer catalog yields good agreement in
redshift and richness estimates; comparing our catalog with the South Pole
Telescope (SPT) selected clusters shows no inconsistencies. SPT clusters in our
dataset are consistent with the high mass extension of the RASS based
$\lambda_{\mathrm{MCMF}}$-mass relation
