X-Ray Spectral Properties of Hot Gas Cavities around NGC 4636

Abstract

Abstract A Chandra observation of NGC 4636 revealed that X-ray hot gas is violently disturbed. We investigated the detailed distributions of the temperature and absorption of hot gas, in order to derive information about the gas dynamics. The temperature gradually increases from 0.6 keV at the center to 0.78 keV at 2 arcmin of the galaxy center; this is consistent with previous measurements. On the other hand, the azimuthal profiles of the temperature and absorption strongly correlate with the disturbance of hot gas. The west part, at 80 arcsec from the galaxy center, exhibits a higher temperature by 0.1–0.2 keV and an excess absorption by $\sim 5 \times 10^{20} \,\mathrm{cm}^{-2}$ compared with the azimuthal averages. This unusual region corresponds to the western X-ray cavity with a size of 20 arcsec radius. The same behavior is also seen around the northeast cavity with a smaller size than the west part. It is suggested that these unusual regions were caused by dramatic outflow or jet from the galactic nuclei, considering the east–west symmetry. The outflow gas or jet might have disturbed the surrounding hot gas and created hole-like regions. The observed high temperature and excess absorption of unusual regions indicate that the rims of holes might have been compressed, heated, and then cooled down at the end stage. We also discuss the past possible nuclear activity in NGC 4636.