Populations of super-soft X-ray sources in galaxies of different morphological types

Vol. 646
Sect. 4. Extragalactic astronomy

Populations of super-soft X-ray sources in galaxies of different morphological types

Super soft X-ray sources (SSS) are white dwarfs onto which thermonuclear burning on their surface is ongoing, thanks to matter accreted from a companion star. They were first observed in our Galaxy and in the Magellanic Clouds, towards which the interstellar absorption is low. With the advent of Chandra and XMM-Newton, some SSS sources were also observed in external galaxies. In this paper, Galiullin & Gilfanov perform a population study on nearby galaxies with deep Chandra observations. They looked for soft and super-soft sources. Soft sources were found to be present in spiral galaxies only and connected to supernova remnants. SSS sources are more frequently observed in spiral galaxies by a factor of ∼8 more than in elliptical galaxies. However, the overall number is small and, unless X-ray absorption in the host galaxy plays a major role, they are not the major class of progenitors for Type Ia supernova.