Soft X-Ray Energy Spectra in the Wide-field Galactic Disk Area Revealed with HaloSat
ASTROPHYSICAL JOURNAL(2024)
摘要
We analyzed data from HaloSat observations for five fields in the Galactic disk located far away from the Galactic center (135(degrees) < l < 254(degrees)) to understand the nature of soft X-ray energy emission in the Galactic disk. The fields have 14(degrees) diameter and were selected to contain no significant high-flux X-ray sources. All five HaloSat soft X-ray energy spectra (0.4-7 keV with energy resolution of < 100 eV below 1 keV) show a possibility of the presence of unresolved high-temperature plasma in the Galactic disk (UHTPGD) with a temperature of 0.8-1.0 keV and an emission measure of (8-11) x 10(-4) cm(-6) pc in addition to the soft X-ray diffuse background components mainly studied at higher Galactic latitudes (solar wind charge exchange emission, Local Hot Bubble, Milky Way halo emission, and the cosmic X-ray background). This suggests that the UHTPGD is present across the whole Galactic disk. We also observed UHTPGD emission in a region with no bright sources in an XMM-Newton field contained within one of the HaloSat fields. The temperature and emission measure are consistent with those measured with HaloSat. Moreover, the stacked spectra of the X-ray pointlike sources and near-infrared-identified point sources such as stars in the XMM-Newton field also show a spectral feature similar to the UHTPGD emission. This suggests that the UHTPGD may partly originate from pointlike sources such as stars.
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关键词
X-ray astronomy,Diffuse x-ray background,Galaxy disks,Galaxy stellar disks,the Milky Way
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