Optimal Chandra/XMM-Newton Band-Passes for Detecting Low Temperature Groups and Clusters of Galaxies

Abstract

In this short paper I present the results of a calculation which seeks the maximum, or optimal, signal-to-noise energy band for galaxy group or cluster X-ray emission detected by the Chandra and XMM-Newton observatories. Using a background spectrum derived from observations and a grid of models I show that the "classical" 0.5-2 keV band is indeed close to optimal for clusters with gas temperatures >2 keV, and redshifts z<1. For cooler systems however, this band is generally far from optimal. Sub-keV plasmas can suffer 20-60% signal-to-noise loss compared to an optimal band, and worse for z>0. The implication is that current and forthcoming surveys should be carefully constructed in order to minimize bias against the low mass, low temperature end of the cluster/group population.