[Paper Review] ROSAT PSPC X-ray observations of the nearby spiral galaxy M83

M. Ehle, W. Pietsch+2 more|arXiv (Cornell University)|Nov 7, 1997

Astrophysical Phenomena and Observations2 references3 citations

TL;DR

This study presents ROSAT PSPC X-ray observations of the nearby face-on spiral galaxy M83, revealing 13 point sources and extended soft and hard X-ray emission. It identifies a two-temperature thermal plasma: a soft X-ray-emitting warm halo (10–15 kpc radius) and a hard X-ray-emitting hot disk component, with plasma beta ≈ 0.2, indicating magnetic fields significantly influence the halo's structure and gas outflow driven by intense star formation.

ABSTRACT

The nearly face-on SBc galaxy M83 (NGC 5236) was observed for 25 ksec with the ROSAT PSPC. We detected 13 point-like sources in this galaxy, 10 of which were previously unknown. We measured extended X-ray radiation from almost the whole optically visible galaxy. Comparing the diffuse soft and hard X-ray emission components, we observed a different asymmetric distribution and a slower radial decrease of the intensity profile of the soft X-ray emission. Both these results support the existence of a huge spherical gas halo of 10-15 kpc radius. On the other hand, the radial scale lengths of the hard X-ray radiation, that of the thermal radio emission and the profile of the optical surface brightness are similar, favouring the idea that all these emission processes are connected to star formation in the galaxy's disk. M83 is the first face-on galaxy where the diffuse X-ray emission spectrum can be characterized by a two-temperature thermal plasma: a soft X-ray emitting warm `halo component' and an internally absorbed hot `disk component' which is dominating the emission in the hard (0.5-2.0 keV) ROSAT energy range. The combination of X-ray and radio polarization observations allows an estimate of the plasma parameter beta = U_therm/U_magn which is found to be 0.2+/-0.1. This result supports the hypothesis that magnetic fields play an important role for the evolution and structure of galactic gas haloes. The high energy input rate in the active star-forming disk of M83 seems to be responsible for the outflow of hot gas and the halo formation.

Motivation & Objective

• To characterize the diffuse X-ray emission in the nearby spiral galaxy M83 using ROSAT PSPC data.
• To investigate the spatial and spectral properties of soft and hard X-ray components and their connection to star formation.
• To determine the role of magnetic fields in shaping the galactic X-ray halo through plasma parameter estimation.
• To assess the origin of extended X-ray emission and its implications for galactic outflows and gas halo formation.

Proposed method

• ROSAT PSPC observed M83 for 25 ksec, enabling deep X-ray imaging and spectroscopy.
• Point-source detection and background subtraction were applied to isolate 13 X-ray sources, 10 previously unknown.
• Radial intensity profiles of soft and hard X-ray emission were measured and compared to optical and radio surface brightness profiles.
• Spectral fitting of the diffuse emission revealed a two-temperature thermal plasma model: a warm halo and a hot disk component.
• Radio polarization data were combined with X-ray data to estimate the plasma beta parameter (U_therm/U_magn).
• The radial scale lengths of hard X-ray, thermal radio, and optical emissions were compared to assess their physical linkage.

Experimental results

Research questions

• RQ1 What is the spatial distribution of soft and hard X-ray emission in M83, and how do they differ?
• RQ2 What is the origin of the extended X-ray emission, and does it indicate a galactic halo?
• RQ3 How do the radial scale lengths of X-ray, radio, and optical emissions compare, and what does this imply for star formation?
• RQ4 What is the role of magnetic fields in the structure and evolution of the X-ray halo, as quantified by plasma beta?
• RQ5 What drives the formation of the hot gas halo in M83, and how is it related to star formation activity?

Key findings

• The diffuse soft X-ray emission exhibits an asymmetric distribution and a slower radial decline, supporting the existence of a spherical gas halo with a radius of 10–15 kpc.
• The hard X-ray emission, dominant in the 0.5–2.0 keV ROSAT band, has a radial scale length similar to that of the optical and thermal radio emission, indicating a link to star formation in the disk.
• M83 is the first face-on galaxy where the diffuse X-ray spectrum is characterized by a two-temperature thermal plasma: a warm halo and a hot disk component.
• The plasma beta parameter, estimated using combined X-ray and radio polarization data, is 0.2 ± 0.1, indicating that magnetic pressure plays a significant role in the halo's structure.
• The high energy input rate from star formation in M83's disk is responsible for driving hot gas outflows and forming the extended X-ray halo.