Galaxy clusters exhibit regular scaling relations among their bulkproperties, establishing vital links between halo mass and clusterobservables. Therefore, precision cosmology studies depending on theselinks benefit from a better understanding of scatter in themass-observable scaling relations. Here, we study the role of mergerprocesses in introducing scatter into the mass-temperature ($M\mhyphenT_X$) relation, using a sample of 121 galaxy clusters simulated withradiative cooling and supernova feedback, along with threemorphological statistics previously proposed to measure X-ray surfacebrightness substructure. These are the centroid variation ($w$), theaxial ratio ($\eta$), and the power ratios ($P_{20}$) and$P_{30}$). We also examine spectral statistics which do not requireimaging. In particular we look at the ratio of hardband to broadbandspectral-fit temperatures $T_{HBR}$, which is a measure of temperatureinhomogeneity inferred from X-ray spectral properties. We find thatin this set of simulated clusters, each substructure measure iscorrelated with a cluster's departures $\delta \ln T$ and $\delta \lnM$ from the mean $M\mhyphen T_X$ relation, both for emission-weightedtemperatures $T_{EW}$ and for spectroscopic-like temperatures$T_{SL}$, in the sense that clusters with more substructure tend to becooler at a given halo mass. In all cases, a three-parameter fit tothe $M\mhyphen T_X$ relation that includes substructure informationhas less scatter than a two-parameter fit to the basic $M\mhyphen T_X$relation. In this work we also test the effectiveness of $T_{HBR}$ asa measure of scatter using the 118 galaxy clusters from our sample forwhich we have simulated X-ray images using the \xmas2 software. Wefind that, while $T_{HBR}$ is correlated with clusters' departures$\delta \ln M$ from the mean $M\mhyphen T_X$ relation, the effect ismodest. Finally, we present the CosmoSurvey software for efficientlyevaluating simple flux-limited galaxy cluster survey models oncommodity hardware, and discuss possible extensions.
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