A volume-limited sample of X-ray galaxy groups and clusters - II. X-ray cavity dynamics

TL;DR

This study analyzes X-ray cavities in a volume-limited sample of galaxy groups and clusters, revealing insights into AGN activity, cavity dynamics, and their role in offsetting cooling, with implications for understanding galaxy evolution.

Contribution

It provides the first comprehensive analysis of cavity energetics and duty cycles in a volume-limited sample, highlighting the importance of continuous AGN activity in offsetting cooling.

Findings

X-ray cavities are present in 30% of the sample with central cooling times less than 3 Gyr.

The AGN duty cycle exceeds 80% for cooling times under 0.5 Gyr, indicating frequent AGN activity.

Larger bubbles tend to travel faster and may result from merging smaller bubbles over multiple cycles.

Abstract

We present the results of our study of a volume-limited sample (z <= 0.071) of 101 X-ray galaxy groups and clusters, in which we explore the X-ray cavity energetics. Out of the 101 sources in our parent sample, X-ray cavities are found in 30 of them, all of which have a central cooling time of less than3 Gyr. New X-ray cavities are detected in three sources. We focus on the subset of sources that have a central cooling time of less than 3 Gyr, whose active galactic nucleus (AGN) duty cycle is approximately 61 percent (30/49). This rises to over 80 percent for a central cooling time of less than 0.5 Gyr. When projection effects and central radio source detection rates are considered, the actual duty cycle is probably much higher. In addition, we show that data quality strongly affects the detection rates of X-ray cavities. After calculating the cooling luminosity and cavity powers of each source with cavities, it is evident that the bubbling process induced by the central AGN has to be, on average, continuous, to offset cooling. We find that the radius of the cavities, r, loosely depends on the ambient gas temperature as T^0.5, above about 1.5 keV, with much more scatter below that temperature. Finally, we show that, at a given location in a group or cluster, larger bubbles travel faster than smaller ones. This means that the bubbles seen at larger distances from cluster cores could be the result of the merging of several smaller bubbles, produced in separate AGN cycles.