The Chandra Deep Group Survey -- cool core evolution in groups and clusters of galaxies

We report the results of a study which assembles deep observations with the ACIS-I instrument on the Chandra Observatory to study the evolution in the core properties of a sample of galaxy groups and clusters out to redshifts $z\approx 1.3$. A search for extended objects within these fields yields a total of 62 systems for which redshifts are available, and we added a further 24 non-X-ray-selected clusters, to investigate the impact of selection effects and improve our statistics at high redshift. Six different estimators of cool core strength are applied to these data: the entropy (K) and cooling time ($t_{cool}$) within the cluster core, the cooling time as a fraction of the age of the Universe ($t_{cool}/t_{Uni}$), and three estimators based on the cuspiness of the X-ray surface brightness profile. A variety of statistical tests are used to quantify evolutionary trends in these cool core indicators. In agreement with some previous studies, we find that there is significant evolution in $t_{cool}/t_{Uni}$, but little evolution in $t_{cool}$, suggesting that gas is accumulating within the core, but that the cooling time deep in the core is controlled by AGN feedback. We show that this result extends down to the group regime and appears to be robust against a variety of selection biases (detection bias, archival biases and biases due to the presence of central X-ray AGN) which we consider.Comment: Accepted by MNRAS, 24 pages, 11 figure

Evolution of X-ray properties of galaxy groups

This thesis presents the results from the Chandra Deep Group Survey, a survey dedicated to find high redshift groups of galaxies in deepest observations available in the Chandra archive. The catalogue compiled from this survey contains 26 groups and 36 clusters with available redshifts, with largest redshift being 1.3. This sample has been used to investigate the evolution of the thermal state of the gas at the centre of groups and compare this evolution to that of clusters. Different parameters have been used to quantify the strength of cool cores and it has been showed that groups and clusters have similar evolution of their cool core properties. Both classes of systems have a wide spread in the cool core strength at low redshifts, which then narrows at high redshifts showing a lack of strong cool core systems

Evolution of X-ray Properties of Galaxy Groups

Studies of scaling relations in groups and clusters of galaxies have shown that the X-ray properties of groups deviate the most from the self-similar prediction. This is because groups are more affected by non-gravitational processes due to their shallower potential well, a behaviour which makes groups an ideal class of systems for the study of the impact of feedback. From the observational point of view, the study of the X-ray properties of groups, especially at high redshifts is hindered by their lower surface brightness compared to their more massive counterparts. We present the result from the Chandra Deep Group Survey, a survey dedicated to find high redshift groups in the deepest observations available in the Chandra archive. We found 26 groups and 36 clusters with available redshifts, with largest redshift being 1.3. We have used this sample to investigate the evolution of cool cores in these two classes of systems using cooling time divided by the age of the cluster as a parameter to describe the cooling state. We have found that groups and clusters have similar evolution in their cool core properties. Both classes of systems have a wide spread in the cool core parameter at low redshifts, which then narrows at high redshifts showing a lack of strong cool core systems