Asymmetric, arc minute scale structures around NGC 1275

TL;DR

This paper analyzes complex X-ray substructures around NGC 1275, suggesting they result from past activity of the galaxy's nucleus, involving relativistic plasma bubbles and energy release comparable to X-ray radiation over millions of years.

Contribution

It presents an interpretation of X-ray substructures as bubbles from past nuclear activity, estimating the energy output and proposing future tests with high-resolution observations.

Findings

X-ray surface brightness varies by about 30% azimuthally.

Estimated nuclear power output of NGC 1275 is around 10^45 erg/s.

Substructure likely caused by buoyant bubbles from past activity.

Abstract

ROSAT HRI observations show complicated substructure in the X-ray surface brightness within $\sim$5 arcminutes around NGC 1275 -- the dominant galaxy of the Perseus cluster. The typical amplitude of the variations is of the order of 30% of the azimuthally averaged surface brightness at a given distance from NGC 1275. We argue that this substructure could be related to the activity of NGC 1275 in the past. Bubbles of relativistic plasma, inflated by jets, be forced to rise by buoyancy forces, mix with the ambient intracluster medium (ICM), and then spread. Overall evolution of the bubble may resemble the evolution of a hot bubble during a powerful atmospheric explosion. From a comparison of the time scale of the bubble inflation to the rise time of the bubbles and from the observed size of the radio lobes which displace the thermal gas, the energy release in the relativistic plasma by the active nucleus of NGC 1275 can be inferred. Approximate modeling implies a nuclear power output of the order of $10^{45}$ erg s$^{-1}$ averaged over the last $\sim 3~10^7$ years. This is comparable with the energy radiated in X-rays during the same epoch. Detailed measurements of the morphology of the X-ray structure, the temperature and abundance distributions with Chandra and XMM may test this hypothesis.