Gravitational torques induced by a stellar bar on the interstellar medium of a disk galaxy instigate radial inflow of gas toward the central regions of the galaxy. Accordingly, the presence of a bar should reinforce nuclear star formation activity or the fueling of an active galactic nucleus (AGN). We test this hypothesis by comparing the detection rate and intensity of nuclear H II regions and...

Microquasars provide new insights into: 1) the physics of relativistic jets from black holes, 2) the connection between accretion and ejection, and 3) the physical mechanisms in the formation of stellar-mass black holes. Furthermore, the studies of microquasars in our Galaxy can provide in the future new insights on: 1) a large fraction of the ultraluminous X-ray sources in nearby galaxies, 2) ...

In order to examine the relationship between the black hole mass MBH and stellar velocity dispersion σ∗ in radio-loud active galactic nuclei (AGNs), we study two effects which may cause the uncertainty of black hole mass estimates for radio-loud AGNs: the relativistic beaming effect on the observed optical continuum radiation and the orientation effect on broad emission line width. After correc...

The luminosity distribution of globular clusters shows a dramatic dependence on parent galaxy luminosity. Dwarf galaxies contain far more faint globulars than do luminous galaxies. This difference is significant at the 99.7% level. On the other hand the luminosity distribution of globular clusters in dwarf galaxies does not appear to depend strongly on their host’s morphological type. The dicho...

Low-luminosity AGN (with LX < 1 × 10 42 ergs s) far outnumber ordinary AGN, and are therefore perhaps more relevant to our understanding of AGN phenomena and the relationship between AGN and host galaxies. Many normal galaxies harbor LINER and starburst nuclei, which, together with LLAGN, are a class of “low-activity” galaxies that have a number of surprisingly similar X-ray characteristics, de...

Context. Some previous investigations have found that the fraction (fAGN ) of active galactic nuclei (AGNs) is lower in clusters than in the field. This can result from the suppression of galaxy-galaxy mergers in high-velocity dispersion (σv) clusters, if the formation and/or fueling of AGNs is directly related to the merging process. Aims. We investigate the existence of a relation between fAG...

The detection of resonance absorption lines against known objects such as individual galaxies and clusters of galaxies is a powerful approach for studying the gas content of these systems. We describe an efficient method of identifying background quasars suitable for absorption line studies. In this finding technique, we identify serendipitous X-ray sources, about 1/8 of which are suitably brig...

We report the discovery of a new radio galaxy within the location error box of the γ-ray source 3EG J1735−1500. The galaxy is a double-sided jet source forming a large angle with the line of sight. Optical observations reveal a V ∼ 18 magnitude galaxy at the position of the radio core. Although the association with the EGRET source is not confirmed at the present stage, because there is a compe...

Attempts of Magain et al (2005) to detect the host galaxy of the bright QSO HE0450– 2958 have not been successful. We suggest that the supermassive black hole powering the QSO was ejected from the observed ULIRG at the same redshift and at 1.5 arcsec distance. Ejection could have either be caused by recoil due to gravitational wave emission from a coalescing binary of supermassive black holes o...

Ultra Steep Spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z & 2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has gradually become possible to extend the USS search to sub-mJy levels, thanks to the recent appearance of sensitive low-frequency radio facilities. Here a first detailed analys...