Spectral Modeling of the Charge-exchange X-Ray Emission from M82
Abstract
It has been proposed that the charge-exchange (CX) process at the interface between hot and cool interstellar gases could contribute significantly to the observed soft X-ray emission in star-forming galaxies. We analyze the XMM-Newton/reflection grating spectrometer (RGS) spectrum of M82 using a newly developed CX model combined with a single-temperature thermal plasma to characterize the volume-filling hot gas. The CX process is largely responsible for not only the strongly enhanced forbidden lines of the Kα triplets of various He-like ions but also good fractions of the Lyα transitions of C VI (~87%), O VIII, and N VII (gsim50%) as well. In total about a quarter of the X-ray flux in the RGS 6-30 Å band originates in the CX. We infer an ion incident rate of 3 × 1051 s-1 undergoing CX at the hot and cool gas interface and an effective area of the interface of ~2 × 1045 cm2 that is one order of magnitude larger than the cross section of the global biconic outflow. With the CX contribution accounted for, the best-fit temperature of the hot gas is 0.6 keV, and the metal abundances are approximately solar. We further show that the same CX/thermal plasma model also gives an excellent description of the EPIC-pn spectrum of the outflow Cap, projected at 11.6 kpc away from the galactic disk of M82. This analysis demonstrates that the CX is potentially an important contributor to the X-ray emission from starburst galaxies and also an invaluable tool to probe the interface astrophysics.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2014
- DOI:
- 10.1088/0004-637X/794/1/61
- arXiv:
- arXiv:1408.3207
- Bibcode:
- 2014ApJ...794...61Z
- Keywords:
-
- galaxies: individual: M82;
- galaxies: starburst;
- X-rays: galaxies;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 12 pages, 5 figures