AChandraObservation of the Circinus Galaxy

Abstract

We report on a recent Chandra ACIS-S observation of the Circinus galaxy. These observations confirm that the nuclear spectrum results from reflection of a hard X-ray continuum by "neutral" matter. The nuclear X-ray emission is extended by ~60 pc in the general direction of the optical "ionization cone." An image in the Fe Kα line has been made and shows that this emission extends up to 200 pc from the nucleus. There is also large-scale X-ray emission both along and perpendicular to the galaxy disk. Thermal plasma models for this extended gas indicate temperatures kT ~ 0.6 keV, though cooler photoionized gas is also possible. The X-ray emission from gas in the disk is probably associated with the starburst ring of radius 150-250 pc. The gas extending ~600 pc perpendicular to the disk is closely correlated with the high-excitation optical line emission. In addition to its soft X-ray emission, we tentatively detect a hard component from the gas above the plane; this hard emission may represent nuclear X-rays scattered into our line of sight by electrons in the outflowing wind. A total of 10 compact sources are found in the central kiloparsec of the galaxy. The most luminous has an X-ray luminosity of ≃1040 ergs s-1 and seems to be an X-ray binary in the Circinus galaxy with a black hole mass exceeding 80 M☉.