David A. Smith

In this paper, we focus on the limb-brightened, prolate spheroidal cavity of the radio galaxy Cygnus A, as revealed by the Chandra X-ray Observatory. We use the shock heated, thermal intracluster medium around the expanding cavity to infer the properties of the radio synchrotron-emitting gas inside the cavity. The gas along the N and S edges of the cavity is found to have an average temperature of 6.0 keV, which is hotter than the temperature (4.6 keV) of the adjacent intracluster gas. It is proposed that this hotter gas is intracluster gas shocked by the expanding cavity. The shock is thus inferred to be weak (Mach number 1.3, a value also inferred from the density jump at the cavity edge) and its velocity 1,460 km/s. The total kinetic power of the expansion is found to be 1.2 x 10^{46} erg/s, which is larger than both the total radio power and the power emitted by the entire intracluster medium in the 2 -- 10 keV band. It appears that most of the power of the jets in Cygnus A is currently going into heating the intracluster medium. From the derived pressure inside the cavity, there is no conclusive evidence for a component contributing pressure additional to the magnetic fields and relativistic particles responsible for the synchrotron radio emission. Further, the ratio of energy densities in positive to negative cosmic rays in Cygnus A is between 1 and 100 (the value in our Galaxy).

We present an analysis of the compact X-ray source population in the Seyfert~2 galaxy NGC 1068, imaged with Chandra. We find a total of 84 compact sources, of which 66 are projected onto the galactic disk of NGC 1068. Spectra of the brightest sources have been modeled with both multi-color disk blackbody and power-law models. The power-law model provides the better description of the spectrum for most of these sources. Five sources have 0.4-8 keV intrinsic luminosities greater than 10^{39} erg/s, assuming that their emission is isotropic and that they are associated with NGC 1068. We refer to these sources as Intermediate Luminosity X-ray Objects (IXOs). If these five sources are X-ray binaries accreting with luminosities that are both sub-Eddington and isotropic, then the implied source masses are >7 solar masses, and so they are inferred to be black holes. The brightest source has a much harder spectrum (Gamma = 0.9\pm0.1) than that found in Galactic black hole candidates and other IXOs. It also shows large-amplitude variability on both short-term and long-term timescales. The ratio of the number of sources with luminosities greater than 2.1 x 10^{38} erg/s in the 0.4-8 keV band to the rate of massive star formation is the same, to within a factor of two, for NGC 1068, the Antennae, NGC 5194 (the main galaxy in M51), and the Circinus galaxy. This suggests that the rate of production of X-ray binaries per massive star is approximately the same for galaxies with currently active star formation, including ``starbursts''.

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 \sim 60 pc in the general direction of the optical ``ionization cone''. An image in the Fe K\alpha 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 \sim 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 \sim 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. Ten compact sources are found in the central kpc of the galaxy. The most luminous has an X-ray luminosity of \simeq 10^{40} erg s^{-1} and seems to be an X-ray binary in the Circinus galaxy with a black-hole mass exceeding 80 M_{\odot}.