Journal Article

Feedback under the microscope – I. Thermodynamic structure and AGN-driven shocks in M87

E. T. Million, N. Werner, A. Simionescu, S. W. Allen, P. E. J. Nulsen, A. C. Fabian, H. Böhringer and J. S. Sanders

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 4, pages 2046-2062
Published in print October 2010 | ISSN: 0035-8711
Published online September 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17220.x
Feedback under the microscope – I. Thermodynamic structure and AGN-driven shocks in M87

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We present the first in a series of papers discussing the thermodynamic properties of M87 and the central regions of the Virgo Cluster in unprecedented detail. Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of ∼16 000 independent regions, each with ∼1000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. The ‘X-ray arms’, driven outwards from M87 by the central active galactic nuclei (AGN), are prominent in the brightness, temperature and entropy maps. Excluding the ‘X-ray arms’, the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions, as expected under action of the heat-flux-driven buoyancy instability (HBI). We confirm the presence of a thick (∼40 arcsec or ∼3 kpc) ring of high-pressure gas at a radius of ∼180 arcsec (∼14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M= 1.25. Another, younger shock-like feature is observed at a radius of ∼40 arcsec (∼3 kpc) surrounding the central AGN, with an estimated Mach number M≳ 1.2. As shown previously, if repeated shocks occur every ∼10 Myr, as suggested by these observations, then AGN-driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350–400 arcsec (27–31 kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least ∼1.0 × 106 solar masses of Fe has been lifted and deposited at a radius of 350–400 arcsec; approximately the same mass of Fe is measured in the X-ray bright arms, suggesting that a single generation of buoyant radio bubbles may be responsible for the observed Fe excess at 350–400 arcsec.

Keywords: galaxies: individual: M87; intergalactic medium; X-rays: galaxies: clusters

Journal Article.  8562 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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