Chandra Observations of the Disruption of the Cool Core in A133

Abstract

Wepresent the analysis of a Chandra observation of the galaxy cluster A133, which has a cooling flow core, a central radio source, and a diffuse, filamentary radio source that has been classified as a radio relic. The X-ray image shows that the core has a complex structure. The most prominent feature is a ‘‘ tongue ’’ of emis- sion that extends from the central cD galaxy to the northwest and partly overlaps the radio relic. Spectral analysis shows that the emission from the tongue is thermal emission from relatively cool gas at a temperature of ?1.3 keV. One possibility is that this tongue is produced by Kelvin-Helmholtz (KH) instabilities through the interaction between the cold gas around the cD galaxy and hot intracluster medium. Weestimate the crit- ical velocity and timescale for the KH instability to be effective for the cold core around the cD galaxy.We find that theKHinstability can disrupt the cold core if the relative velocity ise400 km s?1.We compare the results with those of clusters in which sharp, undisrupted cold fronts have been observed; in these clusters, the low-temperature gas in their central regions has a more regular distribution. In contrast to A133, these cluster cores have longer timescales for the disruption of the core by theKHinstability when they are normal- ized to the timescale of the cD galaxy motion. Thus, the other cores are less vulnerable to KH instability. Another possible origin of the tongue is that it is gas that has been uplifted by a buoyant bubble of non- thermal plasma that we identify with the observed radio relic. Fromthe position of the bubble and the radio estimate of the age of the relic source, we estimate a velocity of ?700 km s?1 for the bubble. The structure of the bubble and this velocity are consistent with numerical models for such buoyant bubbles. The energy dissi- pated by the moving bubble may affect the cooling flow in A133. The combination of the radio and X-ray observations of the radio relic suggest that it is a relic radio lobe formerly energized by the central cD rather than a merger shock–generated cluster radio relic. The lobe may have been displaced from the central cD galaxy by the motion of the cD galaxy or by the buoyancy of the lobe.