Engineering topics

Padovani, P.

Publications and source records attributed to Padovani, P..

6 records

NASA NTRS1991

Fanaroff-Riley I galaxies as the parent populations of BL Lacertae objects. III - Radio constraints

There is increasing support for the idea that BL Lacertae objects are dominated by beamed emission from a relativistic jet aligned with the line of sight. If so, the most likely parent objects are Fanaroff-Riley type I (F-R I) radio galaxies. This hypothesis is tested by determining the ratio of number densities of the two populations in a manner appropriate for flux-limited samples. Through a direct comparison of predicted and observed luminosity functions, it is shown that available radio samples of F-R I galaxies and BL Lac objects are fully consistent with the beaming hypothesis. The model makes specific predictions about the luminosity function of BL Lacertae objects and their radio counts below currently observed levels.

Urry, C. M.↗

NASA NTRS1991

The complete sample of 1 Jansky BL Lacertae objects. I - Summary properties

The first well-defined, homogeneous radio sample of 34 BL Lac objects selected from a large-area survey of sources brighter than 1 Jy at 5 GHz is presented. Extensive optical spectroscopy reveals weak emission lines in roughly 3/4 of the 34 BL Lac objects in the sample. Optical imaging reveals that the nearby BL Lac objects are not stellar, and that the surface brightness distribution of the surrounding fuzz is consistent with the host galaxies being bright ellipticals. The results suggest that gravitational lensing may affect three of the 17 high-redshift BL Lac objects in the sample. The observations do not support a microlensing scenario for the low-redshift objects.

Stickel, M.↗

NASA NTRS1990

Fanaroff-Riley I galaxies as the parent population of BL Lacertae objects. I - X-ray constraints

The hypothesis that BL Lacertae objects are a special subset of Fanaroff-Riley type I radio galaxies, namely, those dominated by beamed emission from a relativistic jet aligned with the line of sight, is examined by looking at the relative number densities. The calculation depends primarily on observed quantities, including the X-ray luminosity function of Fanaroff-Riley type I galaxies. The model predicts the X-ray luminosity function of BL Lacertae objects, the shape of the X-ray counts below currently observed fluxes, and the velocity of the X-ray emitting jet. With Fanaroff-Riley type I galaxies as the parent population the flat luminosity function, the observed X-ray number counts, and the partial redshift distribution of BL Lacertae objects can be explained.

Padovani, P.↗

NASA NTRS1990

The mass function of Seyfert 1 nuclei

The first mass function of Seyfert 1 nuclei is derived from optical spectra of the complete CfA sample of Seyfert galaxies by estimating the mass for each object from a dynamical relation. An independent estimate is also derived using a complete infrared-selected sample. The two mass functions are indistinguishable. The mean mass of Seyfert 1 nuclei is about 2 x 10 to the 7th solar masses, and the integrated mass density is about 6 x 10 to the 11th solar masses/cu Gpc. This is approximately two orders of magnitude less than the value inferred from the energetics associated with quasar counts. A careful analysis of the various parameters and assumptions involved suggests that this large difference is not due to systematic errors in the determinations. Therefore, the bulk of mass related to the accretion processes connected with past quasar activity does not reside in Seyfert 1 nuclei. Instead, the remnants of past activity must be present in a much larger number of galaxies, and a one-to-one relation between distant and local active galactic nuclei seems then to be excluded.

Padovani, P.↗

NASA NTRS1989

Active star-forming galaxies in the X ray foreground

Star forming galaxies were discovered as a component of the X-ray background (XRB) in the Einstein deep surveys. Such star forming galaxies may be largely powered by superluminous Population 1 massive X-ray binaries (MXRB), formed in the wake of star formation in regions of low metallicity. The star forming galaxies with moderate numbers of MXRB may evolve into the infrared starburst galaxies found at low redshifts using IRAS (Infrared Astronomy Satellite), and may also be related to those galaxies identified with sub-mJy radio sources. A conservative contribution to the XRB of at least approximately 15 percent, without evolution is estimated. It is shown that moderate evolution leads to a contribution at least equalling that of quasars. Above 3 keV, star forming galaxies may dominate the XRB.

Griffiths, R. E.↗

NASA NTRS1989

X ray constraints on the beaming hypothesis for BL Lacertae objects

BL Lacertae objects may be Fanaroff-Riley type I (FR I) galaxies with a relativistic jet roughly parallel to the line of sight. The ratio of parent objects (FR Is) to beamed objects (BL Lacs) depends only on the jet velocity. Recently this ratio become observable. X-ray-flux-limited samples are used to demonstrate the viability of the beaming hypothesis. In the process, the X-ray luminosity functions of FR I galaxies and BL Lac objects are derived. Their respective contributions to the cosmic X-ray background radiation are calculated.

Padovani, P.↗