Suzaku Spectroscopy of the Extended X-Ray Emission in M17

TL;DR

This study uses Suzaku X-ray spectroscopy to analyze the diffuse X-ray emission in M17, revealing a hot, low-metallicity plasma with uniform temperature and composition across a 5 pc region.

Contribution

First detailed spectral analysis of M17's extended X-ray emission resolving multiple emission lines and characterizing plasma properties with high spatial resolution.

Findings

The diffuse emission is a 3.0 MK optically-thin thermal plasma.

Elemental abundances are 0.1-0.3 solar, with a Ne enhancement.

No significant spatial variation in temperature or composition.

Abstract

We present the results of a Suzaku spectroscopic study of the soft extended X-ray emission in the HII region M17. The spectrum of the extended emission was obtained with a high signal-to-noise ratio in a spatially-resolved manner using the X-ray Imaging Spectrometer (XIS). We established that the contamination by unresolved point sources, the Galactic Ridge X-ray emission, the cosmic X-ray background, and the local hot bubble emission is negligible in the background-subtracted XIS spectrum of the diffuse emission. Half a dozen of emission lines were resolved clearly for the first time, including K lines of highly ionized O, Ne, and Mg as well as L series complex of Fe at 0.5--1.5 keV. Based on the diagnosis of these lines, we obtained the following results: (1) the extended emission is an optically-thin thermal plasma represented well by a single temperature of 3.0 +/- 0.4 MK, (2) the abundances of elements with emission lines in the diffuse spectrum are 0.1--0.3 solar, while those of bright discrete sources are 0.3--1.5 solar, (3) the metal abundances relative to each other in the diffuse emission are consistent with solar except for a Ne enhancement of a factor of 2, (4) both the plasma temperature and the chemical composition of the diffuse emission show no spatial variation across the studied spatial scale of about 5 pc.