Unravelling ICM Physics and AGN Feedback with Deep Chandra Observations of NGC 5813
Abstract
We present results based on very deep (650 ks) Chandra observations of the galaxy group NGC 5813. This system shows three pairs of collinear cavities, with each pair associated with an elliptical AGN outburstshock. Due to the relatively regular morphology of this system, and the unique unambiguous detection of three distinct AGN outburstshocks, it is particularly well-suited for the study of AGN feedbackand the AGN outburst history. The implied mean kinetic power is roughly the same for each outburst, demonstrating that the average AGN kinetic luminosity can remain stable over long timescales (roughly 50Myr). The two older outbursts have larger, roughly equal total energies as compared with the youngest outburst, implying that the youngest outburst is ongoing. We find that the radiative cooling rate and the mean shock heating rate of the gas are well balanced at each shock front, suggesting that AGN outburst shock heating alone is sufficient to offset cooling and establish AGN/ICM feedback within at least the central 30 kpc. This heating takes place roughly isotropically and most strongly at small radii, as is required for feedback to operate. We suggest that shock heating may play a significant role in AGN feedback at smaller radii in other systems, where weak shocks are more difficult to detect. We find non-zero shockfront widths that are too large to be explained by particle diffusion. Instead, all measured widths are consistent with shock broadening due to propagation through a turbulent ICM with a mean turbulent speed of roughly 70 km/s. Significant contributions to our understanding of AGN feedback and ICM physics, partially via studies similar to the one described here, will be one of the major achievements of the Athena mission.
- Publication:
-
Exploring the Hot and Energetic Universe: The first scientific conference dedicated to the Athena X-ray observatory
- Pub Date:
- September 2015
- Bibcode:
- 2015eheu.conf...44R