X-ray Spectroscopic Evidence of Charge Exchange Emission in the Disk of M51

Abstract

In the disks of spiral galaxies, diffuse soft X-ray emission is known to be strongly correlated with star-forming regions. However, this emission is not simply from a thermal-equilibrium plasma and its origin remains greatly unclear. In this work, we present an X-ray spectroscopic analysis of the emission from the northern hot spot; a region with enhanced star-formation off the nucleus of M51. Based on the high spectral resolution data from XMM-Newton/RGS observations, we unambiguously detect a high $G$ ratio ($3.2_{-1.5}^{+6.9}$) of the OVII He$\alpha$ triplet. This high $G$ ratio is also spatially confirmed by oxygen emission-line maps from the same data. A physical model consisting of a thermal plasma and its charge exchange (CX) with neutral cool gas gives a good explanation for the $G$ ratio and the entire RGS spectra. This model also gives a satisfactory characterization of the complementary Chandra/ACIS-S data, which enables a direct imaging of the diffuse emission, tracing the hot plasma across the galaxy. The hot plasma has a similar characteristic temperature of ~0.34 keV and an approximately solar metallicity. The CX contributes ~50% to the diffuse emission in the 0.4-1.8 keV band, suggesting an effective hot/cool gas interface area about five times the geometric area of the M51 disk. Therefore, the CX appears to play a major role in the soft X-ray production and may be used as a powerful tool to probe the interface astrophysics, important for studying galactic ecosystems.

13 pages, 6 figures, 2 tables, published in ApJ

References in corpus (10)

• Line Ratios for Solar Wind Charge Exchange with Comets
• Spectral Modeling of the Charge-Exchange X-ray Emission from M82
• Can nebular HeII emission be explained by ultra-luminous X-ray sources?
• Gas and stellar spiral arms and their offsets in the grand-design spiral galaxy M51
• High-resolution X-ray spectroscopy and imaging of the nuclear outflow of the starburst galaxy NGC 253
• An XMM-Newton view of M101 - III. Diffuse X-ray emission
• X-ray spectroscopy of the starburst feedback in 30 Doradus
• Deep Chandra observations of diffuse hot plasma in M83
• XMM-Newton RGS spectroscopy of the M31 bulge. I: Evidences for a past AGN half a million years ago
• Spectral Modeling of Charge Exchange in the Central Region of M51

Cited by in corpus (1)

• Studying the multi-phase interstellar medium in the Large Magellanic Cloud with SRG/eROSITA -- I. Analysis of diffuse X-ray emission