High redshift X-ray galaxy clusters^*

I. The impact of point sources on the cluster properties

¹ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: m.branchesi@ira.inaf.it
² INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy e-mail: [gioia;rfanti;cfanti]@ira.inaf.it

Received: 13 March 2007
Accepted: 17 June 2007

Abstract

Context.The current generation of X-ray observatories like Chandra allows studies with very fine spatial details. It is now possible to resolve X-ray point sources projected into the cluster diffuse emission and exclude them from the analysis to estimate the “correct” X-ray observables.

Aims.We wish to verify the incidence of point sources on the cluster thermal emission and to evaluate the impact of their non-thermal emission on the determination of cluster properties.

Methods.To these ends we use a sample of 18 high-z (0.25 < z < 1.01) clusters from the Chandra archive and subtract the non-thermal emission of the point sources from the extended thermal emission due to the cluster itself. We perform a detailed analysis of the cluster properties and compare the changes observed in the X-ray observables, like temperature and luminosity or their inter-relation, when one keeps the point sources in the analysis.

Results.The point sources projected into the cluster extended emission affect the estimates of cluster temperature or luminosity considerably (up to 13% and 17% respectively). These percentages become even larger for clusters with 0.7 where temperature and luminosity increase up to 24% and 22%, respectively.

Conclusions.The conclusions are that point sources should be removed to correctly estimate the cluster properties. However the inclusion of the point sources does not impact significantly the slope and normalization of the L_bol–T relationship since for each cluster the correction to be applied to T and L_bol produces a moderate shift in the L_bol–T plane almost parallel to the best-fit of the “correct” L_bol–T relation.