The unusual X-ray morphology of NGC4636 revealed by deep Chandra observations: cavities and shocks created by past AGN outbursts

TL;DR

Deep Chandra observations of NGC 4636 reveal complex X-ray structures including cavities and shocks, indicating past active galactic nucleus outbursts that shaped the galaxy's hot gas environment.

Contribution

This study provides detailed imaging and analysis of X-ray cavities and shocks in NGC 4636, supporting a shock-driven origin from past AGN activity, which was not previously characterized in such detail.

Findings

Detection of symmetric X-ray bubbles with sharp edges.

Temperature jumps across bubble rims of 20-25%.

Shocks driven by off-center jets likely caused the observed structures.

Abstract

We present Chandra ACIS-I and ACIS-S observations ($\sim$200 ks in total) of the X-ray luminous elliptical galaxy NGC 4636, located in the outskirts of the Virgo cluster. A soft band (0.5-2 keV) image shows the presence of a bright core in the center surrounded by an extended X-ray corona and two pronounced quasi-symmetric, 8 kpc long, arm-like features. Each of this features defines the rimof an ellipsoidal bubble. An additional bubble-like feature, whose northern rim is located $\sim2$ kpc south of the north-eastern arm, is detected as well. We present surface brightness and temperature profiles across the rims of the bubbles, showing that their edges are sharp and characterized by temperature jumps of about 20-25%. Through a comparison of the observed profiles with theoretical shock models, we demonstrate that a scenario where the bubbles were produced by shocks, probably driven by energy deposited off-center by jets, is the most viable explanation to the X-ray morphology observed in the central part of NGC 4636.