High redshift X-ray galaxy clusters

II. The relationship revisited

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

Received: 13 March 2007
Accepted: 17 June 2007

Abstract

Aims.In this paper we re-visit the observational relation between X-ray luminosity and temperature for high-z galaxy clusters and compare it with the local L_X–T and with theoretical models.

Methods.To these ends we use a sample of 17 clusters extracted from the Chandra archive supplemented with additional clusters from the literature, either observed by Chandra or XMM–Newton, to form a final sample of 39 high redshift (0.25 < z <1.3) objects. Different statistical approaches are adopted to analyze the L_X–T relation.

Results.The slope of the L_X–T relation of high redshift clusters is steeper than expected from the self-similar model predictions and steeper, even though still compatible within the errors, than the local L_X–T slope. The distant cluster L_X–T relation shows a significant evolution with respect to the local Universe: high-z clusters are more luminous than the local ones by a factor 2 at any given temperature. The evolution with redshift of the L_X–T relation cannot be described by a single power law nor by the evolution predicted by the self-similar model.

Conclusions.We find a strong evolution, similar or stronger than the self-similar model, from to z ≤ 0.3 followed by a much weaker, if any, evolution at higher redshifts. The weaker evolution is compatible with non-gravitational models of structure formation. According to us a statistically significant sample of nearby clusters (z < 0.25) should be observed with the current available X-ray telescopes to completely exclude observational effects due to different generation detectors and to understand this novel result.