We have found compact X-ray sources in the center of 21 (54%) of 39 nearby face-on spiral and elliptical galaxies with available ROSAT HRI data. ROSAT X-ray luminosities (0.2 - 2.4 keV) of these compact X-ray sources are ~ 1e37 - 1e40 erg/s (with a mean of 3e39 erg/s. The mean displacement between the location of the compact X-ray source and the optical photometric center of the galaxy is ~ 390 pc. The fact that compact nuclear sources were found in nearly all (five of six) galaxies with previous evidence for a black hole or an AGN indicates that at least some of the X-ray sources are accreting supermassive black holes. ASCA spectra of six of the 21 galaxies show the presence of a hard component with relatively steep (Gamma approx 2.5) spectral slope. A multicolor disk blackbody model fits the data from the spiral galaxies well, suggesting that the X-ray object in these galaxies may be similar to a Black Hole Candidate in its soft (high) state. ASCA data from the elliptical galaxies indicate that hot (kT approx 0.7 keV) gas dominates the emission. The fact that (for both spiral and elliptical galaxies) the spectral slope is steeper than in normal type 1 AGNs and that relatively low absorbing columns (N_H approx 1e21 /cm2) were found to the power-law component indicates that these objects are somehow geometrically and/or physically different from AGNs in normal active galaxies. The X-ray sources in the spiral and elliptical galaxies may be black hole X-ray binaries, low-luminosity AGNs, or possibly young X-ray luminous supernovae. Assuming the sources in the spiral galaxies are accreting black holes in their soft state, we estimate black hole masses ~ 1e2 - 1e4 solar masses.Comment: 47 pages AASTEX, 6 postscript figures, plus two landscape tables (postscript), to appear in ApJ, revised version has fewer (single-spaced) page

The recent development of unified theories of active galactic nuclei (AGN) has indicated that there are two physically distinct classes of these objects -radio-loud and radio-quiet. The primary observational distinctions between the two types are: (1) The radio-loud objects produce large scale radio jets and lobes, with the kinetic power of the jets being a significant fraction of the total bolometric luminosity. On the other hand, the weak radio ejecta of the radio-quiet objects are energetically insignificant.(2) The radioloud objects are associated with elliptical galaxies which have undergone recent mergers, while the radio-quiets prefer spiral hosts. (3) The space density of the radio-louds at a given optical luminosity is ≈ 10 times lower than that of the radio-quiets. Despite these differences, the (probably) thermal emissions from the AGN (continua and lines from Xray to infrared wavelengths) are quite similar in the two classes of object. We argue that this last result suggests that the black hole masses and mass accretion rates in the two classes are not greatly different, and that the difference between the classes is associated with the spin of the black hole.We assume that the normal process of accretion through a disk does not lead to rapidly spinning holes, and propose instead that galaxies (e.g. spirals) which have not suffered a recent major merger event contain non-rotating or only slowly rotating black holes. When two such galaxies merge, the two black holes are known to form a binary and we assume that they eventually coalesce. In the small fraction of mergers in which the two "parent" galaxies contain very massive holes of roughly equal mass, a rapidly spinning, very massive hole results. It is proposed that such mergers are the progenitors of powerful radio sources, in which the radio jets are powered by the spin energy of the merged hole. We calculate the distributions of mass and spin for the merged holes from the parent hole mass distribution, which is derived from the optical luminosity function of radio-quiet AGN adopting different activity patterns. The ratio of the number of radio-loud to radio-quiet AGN's at a given thermal (e.g. optical) luminosity is determined by the galaxy merger rate. The required fraction of galaxies which merge during the average lifetime (≈ 10 8 yrs) of a radio-loud

We have analyzed Chandra ACIS observations of 32 nearby spiral and elliptical galaxies and present the results of 1441 X-ray point sources that were detected in these galaxies. The total point-source X-ray (0.3−8.0 keV) luminosity L XP is well correlated with the B-band, K-band, and FIR+UV luminosities of spiral host galaxies, and is well correlated with the B-band and K-band luminosities for elliptical galaxies. This suggests an intimate connection between L XP and both the old and young stellar populations, for which K and FIR+UV luminosities are reasonable proxies for the galaxy mass M and star-formation rate SF R. We derive proportionality constants α = 1.3 × 10 29 erg s −1 M −1

We investigate how the empirical properties of hot X-ray-emitting gas in a sample of seven starburst and three normal edge-on spiral galaxies (a sample that covers the full range of star formation intensity found in disk galaxies) correlate with the size, mass, star formation rate, and star formation intensity in the host galaxies. From this analysis we investigate various aspects of mechanical energy ''feedback''-the return of energy to the interstellar medium from massive star supernovae and stellar winds-on galactic scales. The X-ray observations make use of the unprecedented spatial resolution of the Chandra X-Ray Observatory to remove X-ray emission from point sources more accurately than in any previous study and hence obtain the X-ray properties of the diffuse thermal emission alone. Intriguingly, the diffuse X-ray properties of the normal spirals (in both their disks and halos) fall where extrapolation of the trends from the starburst galaxies with superwinds would predict. We demonstrate, using a variety of multiwavelength star formation rate and intensity indicators, that the luminosity of diffuse X-ray emission in the disk (and, where detected, in the halo) is directly proportional to the rate of mechanical energy feedback from massive stars in the host galaxies. Accretion of gas from the intergalactic medium (IGM) does not appear to be a significant contributor to the diffuse X-ray emission in this sample. Nevertheless, with only three nonstarburst normal spiral galaxies it is hard to exclude an accretion-based origin for extraplanar diffuse X-ray emission around normal star-forming galaxies. Larger galaxies tend to have more extended X-ray-emitting halos, but galaxy mass appears to play no role in determining the properties of the disk or extraplanar X-ray-emitting plasma. The combination of these luminosity and size correlations leads to a correlation between the surface brightness of the diffuse X-ray emission and the mean star formation rate per unit area in the disk (calculated from the far-infrared luminosity and the optical size of the galaxy, L FIR =D 2 25 ). Further observational work of this form will allow empirical constraints to be made on the critical star formation rate per unit disk area necessary to blow hot gas out of the disk into the halo. We show that a minor generalization of standard superbubble theory directly predicts a critical star formation rate per unit area for superbubble blowout from the disk and by extension for superwinds to blow out of the gaseous halos of their host galaxy. At present there are a variety of poorly known parameters in this theory that complicate comparison between observation and theory, making it impossible to assess the quantitative accuracy of standard superbubble blowout theory. We argue that the crucial spatial region around a galaxy that controls whether gas in starburst-driven superwinds will escape into the IGM is not the outer halo $100 kpc from the host galaxy, but the inner few halo scale heights, within $20 kpc of the galaxy plan...

See http://www.xassist.org/ixocat hri for figures and future updates of this catalog. NOTE -some IXO numbers have changed since the original astro-ph submission. This paper is now accepted into the ApJ Supplements, and Tables 1 and 2 comprise version 2.0 of our ROSAT HRI IXO catalog.ROSAT, and now Chandra, X-ray images allow studies of extranuclear Xray point sources in galaxies other than our own. X-ray observations of normal galaxies with ROSAT and Chandra have revealed that off-nuclear, compact, Intermediate-luminosity (L X [2-10 keV] ≥10 39.0 erg s −1 ) X-ray Objects (IXOs, a.k.a. ULXs [Ultraluminous X-ray sources]) are quite common. Here we present a catalog and finding charts for 87 IXOs in 54 galaxies, derived from all of the ROSAT HRI imaging data for galaxies with cz ≤ 5000 km s −1 from the Third Reference Catalog of Bright Galaxies (RC3). We have defined the cutoff L X for IXOs so that it is well above the Eddington luminosity of a 1.4 M ⊙ black hole (10 38.3 erg s −1 ), so as not to confuse IXOs with "normal" black hole X-ray binaries. This catalog is intended to provide a baseline for follow-up work with Chandra and XMM, and with space-and ground-based survey work at wavelengths other than X-ray. We demonstrate that elliptical galaxies with IXOs have a larger number of IXOs per galaxy than non-elliptical galaxies with IXOs, and note that they are not likely to be merely high-mass X-ray binaries with beamed X-ray emission, as may be the case for IXOs in starburst galaxies. Approximately half of the IXOs with multiple observations show X-ray variability, and many (19) of the IXOs have faint optical counterparts in DSS optical B-band images. Follow-up observations of these objects should be helpful in identifying their nature.