X-ray and optical view of HCG 16 compact group of galaxies

<p>HCG 16 is a rare (very compact) group of galaxies made of solely spiral galaxies showing diffuse X-ray emission. The figure shows optical (greyscale from the Digitized Sky Survey) and X-ray (contours, Chandra ACIS-S3, ObsID 923, PI Mamon) views of HCG 16. Chandra chip is 8 arcmin across. The four luminous galaxies are (left to right) NGC 839 (HCG 16d), NGC 838 (HCG 16c), NGC 835 (HCG 16a) and NGC 833 (HCG 16b). The Chandra contours are for the energy band 0.4–1.57 keV. This unpublished image was corrected for the exposure map in 4 energy bands, and processed with CIAO 2.2.1 in March 2002.