Luminosity Radio Galaxies Research Articles

Relativistic jets and the nature of BL Lacertae objects

BL Lacertae objects are an extreme form of Active Galactic Nuclei characterized by rapid variability, high polarization, a compact radio structure, and weak emission lines. Most of these properties can be understood as consequences of a relativistic jet. The simplest model of a jet is a single homogeneous sphere of plasma emitting synchrotron and inverse—Compton radiation which is moving at relativistic speeds close to the line of sight. While real sources cannot be explained in detail with such a model, it provides a valuable framework for understanding the observational consequences of relativistic jets. More complex models involving the superposition of homogeneous regions each with different physical parameters are better able to match the radio — X-ray spectrum of BL Lacertae objects, although the model parameters are generally not well constrained. If BL Lacertae objects are indeed sources with jets oriented close to the line of sight then intrinsically identical objects must exist which just happen to have jets pointed away. A “unified scheme” for BL Lacertae objects identifies low luminosity radio galaxies as those objects. Comparisons of the properties of large samples of radio galaxies and BL Lacertae objects are valuable tools for constraining the physical parameters of jets in these AGN.

The optical properties of low luminosity radio galaxies with radio jets

view Abstract Citations (39) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Properties of Low Luminosity Radio Galaxies With Radio Jets Gonzalez-Serrano, J. I. ; Carballo, R. ; Perez-Fournon, I. Abstract Broad-band CCD images of 24 low luminosity radio galaxies containing radio jets have been obtained to study their optical properties. Surface photometry of the galaxies was performed by fitting ellipses to the light distribution in order to obtain the surface brightness profile and the geometrical parameters of the galaxies. The optical morphology, the photometric parameters, and the local environment of the galaxies are discussed and compared with the results for other galaxy samples. The galaxies in this work have absolute magnitudes similar to bright cluster galaxies, and they are more luminous than powerful radio sources. They inhabit regions of higher galaxy density than powerful radio galaxies and radio-quiet ellipticals. A fraction as large as 75% of the galaxies show morphological peculiarities in the optical, indicating gravitational interaction with nearby companions and/or recent merging. We argue that low luminosity radio galaxies could be the precursors of cD galaxies in clusters or groups of galaxies, on the basis of their optical luminosity, the local environment, presence of extended envelopes, indications of merging processes, x-ray emission, and presence of dumbbell systems and multiple nuclei. Publication: The Astronomical Journal Pub Date: May 1993 DOI: 10.1086/116548 Bibcode: 1993AJ....105.1710G Keywords: Astronomical Photometry; Luminous Intensity; Optical Properties; Radio Galaxies; Radio Jets (Astronomy); Charge Coupled Devices; Data Reduction; Galactic Structure; Radial Velocity; Astrophysics; RADIO CONTINUUM: GALAXIES; GALAXIES: FUNDAMENTAL PARAMETERS; GALAXIES: JETS full text sources ADS | data products SIMBAD (25) NED (24)

IC5063: A Merger with A Hidden Luminous Active Nucleus

Despite intense theoretical and observational effort during the past few years, two important questions in the field of active galaxies remain open and are the subject of vigorous debate.The first concerns the connection between the interaction/merger of galaxies and the generation of starburst and/or active nuclei. A large fraction of high luminosity radio galaxies (Baum et al. 1988), quasars (Hutchinga, 1987) and IRAS galaxies (Sanders et al. 1988), show the presence of a large companion or have a peculiar optical morphology which is offen interpreted as evidence of a recent merger or interaction. In Seyferts, there are also several examples of individual galaxies with clear evidence of interaction/merger (Colina et al. 1987; Fricke and Kollatschny, 1989; Macchetto et al. 1990). Also a significant fraction of low luminosity radio galaxies are associated with a system of two elliptical galaxies in interaction (Colina and Pérez-Fournon, 1990a,b).

Morphological properties of radio elliptical galaxies

A CCD imaging survey of elliptical galaxies which present radio jets is described. The photometric and morphological properties of these galaxies and their nearby companions are described by Fourier analysis of the intensity variations along a set of elliptical contours fitted to the intensity distribution. A large fraction of the sample shows evidence for interaction with close companions. By interpolation between the best-fit ellipses an elliptical galaxy model of the underlying stellar distribution is constructed and by subtraction of these models interesting morphological features such as ‘boxy’ isophotes, dust lanes and emission line regions are revealed. The data analysis technique developed for this study is described. The morphological and photometric properties of the objects can be explained by gravitational interaction of galaxies in close encounters. Five objects of a complete sample of low luminosity radio galaxies are briefly discussed.

Disruption of galactic radio jets by shocks in the ambient medium

Observations show that jets in moderate luminosity (<1025 W Hz−1 at 20 cm wavelength) radio galaxies can flare dramatically in a few jet diameters and with opening angles up to 90° into diffuse lobes or tails1–4 (Fig. 1). These morphologies are difficult to reproduce in numerical simulations of supersonic jets that move outward in constant5,6 or smoothly varying atmospheres (N. Norman, unpublished results). By analogy with structures seen in the laboratory7, one could interpret the collimated jets as moderately supersonic (Mach number 2–5) fluid flows, and the lobes or tails as subsonic plumes that are subject to turbulent broadening and entrainment of the ambient medium. Our studies indicate that the transition from supersonic to subsonic flow can occur suddenly only if a strong planar (normal to the flow direction) shock or Mach disk forms within the jet. Here we show that such an internal shock is produced as the jet crosses a shock wave in the external medium. The external shock could form, for example, by a galactic wind encountering the intergalactic medium. We find that for jet disruption the jet Mach number must be less than the wind-shock Mach number, a result also understandable from analytic arguments. We apply this model to Cen A and wide-angle-tailed radio galaxies.

Westerbork Observations of Low Luminosity Radio Sources

The two radio galaxies 0326+39 and 1321+31 are both part of a complete sample of low luminosity radio galaxies which was obtained by identifying B2 radio sources with galaxies from the Zwicky Catalogue. Both sources have a very symmetrical double jet, like many other sources of the sample (Ekers et al. 1981a).

High Resolution VLA Observations of Quasars with Distorted Radio Stucture

Most quasars with extended radio structures have the classical linear double structure (Class II) which is also characteristic of the most luminous radio galaxies. A very small fraction of quasars do, however, show deviations from the classical double structure which are similar to the distortions observed in some low luminosity radio galaxies, e.g., bent double sources. Among radio galaxies, structural distortions seem to be associated with membership in a cluster of galaxies. Indeed, Scott and Hintzen, 1978, have suggested that such distortions might be indicators of cluster membership for quasars as well. To test this hypothesis and examine the physics of distorted quasars, we have mapped the quasars 3C 270.1 and 3C 275.1 in both I and P using the VLA A-Array at 20 cm and 6 cm. Our high resolution (0.1 arc sec at 6 cm) and high dynamic range (200:1) observations demonstrate that the displaced components reported previously for these sources are indeed connected with the quasars themselves and, therefore, the distortions are not simply projection effects. We also report the discovery of a very narrow northwesterly pointing jet in the quasar 3C 275.1.