AWOB Science Cases

MPDL,GAVO

 Science Cases for the AWOB Demonstrator 

ROSAT PSPC Observations of the Edge-On Galaxy NGC 253
From Pietsch et al. 2000, A&A 360, 24

Target
The edge-on spiral galaxy NGC 253, southern hemisphere, X-ray observations with the ROSAT satellite

Scientific Motivation
Due to the low galactic foreground, diffuse X-ray emission at several million K should be visible out of the disk and the halo. Such an emission component, best visible in the ROSAT 0.1-0.4 keV band, was already indicated by Einstein observations. To map the diffuse emission, long observation times (several dozen ks) have been requested.

Science Task
Visualize the ROSAT soft (0.1-0.4 keV) and hard (0.5-2.0 keV) band X-ray images (fits-files) available under soft band and hard band. An appropriate Gaussian filter has been applied to both images. Overlay the contours of these images onto an optical plate (e.g., DSS2 image by ESO – you can load it in Aladin). Suggested contour levels are 35,60,90,120,150,170,200 for the hard band and 105,135,165,195 for the soft band, repsectively. If you use Aladin, switch the “Use smoothing” option off. Build a two color image (red for soft X-rays, blue for hard X-rays) to further visualize the two different emission components.

Scientific Results
The hard emission mainly traces point sources in the disk and the central starburst region. The diffuse X-ray emission in the hard band is mostly aligned to the disk of the galaxy and is distributed symetrically in the disk. In opposite, the soft X-ray emission clearly protrudes into the halo of the galaxy. Thus, a million K component of the interstellar medium escapes the disk of the galaxy and flows out into the halo. The soft component from the reverse side of the disk is shadowed by the north-western rim of the disk, which is approaching to us.

Figures
ROSAT PSPC soft band contours overlaid onto an optical plate (DSS2, ESO)

ROSAT PSC hard band contours overlaid onto an optical image (DSS2, ESO)

ROSAT PSPC soft band (red color) and hard band (blue color) image combined to a false color image. Contours of the soft band are superimposed onto the image