High-resolution X-ray and radio observations of the giant elliptical galaxies NGC 4636 and 4649

Abstract

Einstein HRI observations of the giant elliptical galaxies NGC 4636 and 4649 reveal that both are extended soft X-ray sources with luminosities ∼1.5 × 1041 erg s−1. Most of the emission probably arises from hot gas with kT ∼ 1 keV, although the complex X-ray morphology in the central region of NGC 4636 may in part be due to groupings of discrete sources. In the case of NGC 4636, the centroid of the X-ray emission is significantly displaced from the radio/optical nucleus of the galaxy. Deprojection of the X-ray data yields gas parameters which are consistent with the presence of cooling accretion flows throughout both galaxies. VLA observations reveal extended radio sources with luminosities ∼1038 erg s−1 in both galaxies. The thermal pressure of the ambient hot gas can strongly confine these radio sources and, through pressure gradients, may give rise to the twisted morphology of the radio source in NGC 4636. The infalling cooling gas may also fuel the radio sources by accretion on to a massive compact object.