Origin of the diffuse 4-8 keV emission in M82

Abstract

We present the first spatially resolved, X-ray spectroscopic study of the 4-8 keV diffuse emission found in the central part of the nearby starburst galaxy M82 on a few arcsecond scales. The new details that we see allow a number of important conclusions to be drawn on the nature of the hot gas and its origin as well as feedback on the ISM. We use archival data from Chandra with an exposure time of 570 ks. The Fexxv emission at 6.7 keV, expected from metal-enriched hot gas, is enhanced only in a limited area close to the starburst disc and is weak or almost absent over the rest of the diffuse emission, resulting in spatial variations in EW from <0.1 keV to 1.9 keV. This shows the presence of non-thermal emission due to inverse Compton scattering of the FIR photons by radio emitting cosmic ray electrons. The morphological resemblance between the diffuse X-ray, radio, and FIR emission maps supports this concept. Our decomposition of the diffuse emission spectrum indicates that ~70% of the 4-8 keV luminosity originates from the inverse Compton emission. The metal-rich hot gas with kT~5 keV makes a minor contribution to the 4-8 keV continuum, but it accounts for the majority of the observed Fexxv line. This hot gas appears to emerge from the circumnuclear starburst ring and fill the galactic chimneys identified as mid-infrared and radio emission voids. The energetics argument suggests that much of the supernova energy in the starburst site has gone into creating the chimneys and is transported to the halo. We argue that a hot, rarefied environment produced by strong supernova feedback results in displacing the brightest X-ray and radio supernova remnants which are instead found to reside in GMC. We find a faint X-ray source with a radio counterpart, close to the kinematic centre of the galaxy and we carefully examine the possibility that this source is a low-luminosity AGN in ADAF phase.

19 pages, accepted for publication in Astronomy & Astrophysics

References in corpus (11)

• Revised equipartition & minimum energy formula for magnetic field strength estimates from radio synchrotron observations
• Iron line and diffuse hard X-ray emission from the starburst galaxy M82
• The WISE Extended Source Catalogue (WXSC) I: The 100 Largest Galaxies
• The Fundamental Plane of Black Hole Accretion and its Use as a Black Hole-Mass Estimator
• Nonthermal X-rays from low-energy cosmic rays: Application to the 6.4 keV line emission from the Arches cluster region
• Deep MERLIN 5GHz Radio Imaging of Supernova Remnants in the M82 Starburst
• A ~60-day super-orbital period originating from the ultraluminous X-ray pulsar in M82
• Discovery of a bright radio transient in M82: a new radio supernova?
• SOFIA Far Infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Super-Galactic Wind
• NOEMA High Fidelity Imaging of the Molecular Gas in and around M82
• X-ray supernova remnants in the starburst region of M82

Cited by in corpus (2)

• A Fast, Hot Wind from a Nuclear Starburst
• Non-thermal emission in the central starburst region of M82