arXiv subjects
Publications and source records attributed to R. Morganti.
We have studied the effects of the interaction between the radio jet and the ambient gas in the powerful radio galaxy PKS2250-41 (z=0.31). Our results show that the gas has been accelerated, compressed, heated and collisionally ionized by the shock. This study helps us to understand the processes which determine the observed properties of many high redshift radio galaxies.
Two frequency observations, mainly at 1.4 and 5 GHz from the VLA, have been used to study spectral variations along the lobes of some nearby low luminosity radio galaxies that constitute a representative sample selected from the B2 catalogue. The variations of the spectral index have been interpreted as being due to synchrotron and inverse Compton losses and characteristic spectral ages are deduced for the relativistic electrons. The radiative ages are in the range of several 10^7 years. These ages correlate well with the source sizes. They also appear to be consistent with dynamical ages determined from ram-pressure arguments, if we make reasonable assumptions about the ambient gas density and allow for very moderate deviations from the equipartition conditions. There appears to be a significant difference between the radiative ages of sources in our sample and those of more powerful 3CR radio sources. We briefly discuss the possibility of re-acceleration processes and indicate some objects where these may occur.
We present here the first results of a 22cm survey of the Shapley Concentration core. The observations were carried out with the Australia Telescope Compact Array. Our radio observations completely and uniformely cover the A3558 complex, allowing a thorough multifrequency study, by comparison of our results with the available optical spectroscopic and X-ray data of the whole chain. We will present here some statistical results of our survey and compare them with the information on the dynamics of the chain and on the properties of the intracluster gas. Attention will also be devoted to the extended radio galaxies found in our survey.
The nature of the optical--radio correlations for powerful radio galaxies is investigated using spectroscopic observations of a complete sample of southern 2Jy radio sources. In line with previous work, we find that significant correlations exist between the luminosities of the [OIII]5007, [OII]3727 and Hbeta emission lines and the radio luminosity. However, our observations are not easily reconciled with the idea that these correlations are caused by the increase in the power of the photoionizing quasar as the jet power increases, with average ISM properties not changing appreciably with redshift or radio power: not only do we find that the scatter in the L_[OIII] vs. L_radio correlation is significantly larger than in L_[OII]} vs. L_radio and L_Hbeta vs. L_radio correlations, but the ionization state deduced from the emission lines does not increase with radio power as predicted by the simple, constant ISM, photionization model. We conclude that: (a) there exists a considerable range in the quasar ionizing luminosity at a given redshift; and (b) that the mean density of the emission line clouds is larger in the high redshift/high power radio sources. The latter density enhancement may either be a consequence of the increased importance of jet-cloud interactions or, alternatively, due to a higher pressure in the confining hot ISM, in the high redshift objects. Deep spectra show that many of the sources in our sample are broad line radio galaxies (BLRG). The fact that the BLRG are observed out the redshift limit of the survey, overlapping in redshift with the quasars, argues against the idea that BLRG are simply the low radio power counterparts of high power, high redshift quasars.
In this paper we present a detailed study of the radio galaxy J1324-3138, located at a projected distance of 2 arcmin from the centre of the Abell cluster of galaxies A3556, belonging to the core of the Shapley Concentration, at an average redshift z=0.05. We have observed J1324-3138 over a wide range of frequencies: at 327 MHz (VLA), at 843 MHz (MOST), and at 1376 MHz, 2382 MHz, 4790 MHz and 8640 MHz (ATCA). Our analysis suggests that J1324-3138 is a remnant of a tailed radio galaxy, in which the nuclear engine has switched off and the radio source is now at a late stage of its evolution, confined by the intracluster gas. The radio galaxy is not in pressure equilibrium with the external medium, as it is often found for extended radio sources in clusters of galaxies. We favour the hypothesis that the lack of observed polarised radio emission in the source is due to Faraday rotation by a foreground screen, i.e. the source is seen through a dense cluster gas, characterised by a random magnetic field. An implication of the head-tail nature of the source is that J1324-3138 is moving away from the core of A3556 and that possibly a major merging event between the core of A3556 and the subgroup hosting J1324-3138 has already taken place.
We have collected emission line ([Oiii] 5007 and Halpha+[Nii]) and radio continuum images for a volume limited (cz <= 3600 km/s) sample of southern Seyfert galaxies. The optical data were obtained at ESO using the 2.2 m, NTT and 3.6 m telescopes, and have a typical resolution of 1" and noise level of ~1e-16 ergs cm-2 s-1 arcsec-2. The radio continuum observations were obtained with the VLA (6 cm) and ATCA (3 cm) and have a resolution of ~1" matching that of the optical images. All, but one of the observed sources were detected above the noise limit of ~0.15 mJy. In the radio, 30% of the sources show linear structure, 25% are only slightly resolved or diffused, and 45% remain unresolved at the ~1" resolution. As in previous work, a correlation is found between the size of the radio structure and the radio power. The radio sources in Seyfert 2 galaxies have, on average, larger linear size than their type 1 counterparts, but there is no significant difference in radio power between types 1 and 2. No significant difference is found in the spectral indices of the two Seyfert types. Extended emission is common in Seyfert galaxies -- essentially all objects observed show extended Halpha+[Nii] and nearly 50% show extended [Oiii] emission. At least 40% (18 out of 50) of the galaxies show high excitation extended emission line region (EELR) well outlined in the excitation map. The EELR morphology vary from linear to conical to S-shaped and even X-shaped. Almost exclusively all elongated EELR are in Seyfert 2 galaxies. The orientation of the EELR appears to be random relative to either the major (or minor) axis or relative to the non-axisymmetric structures, such as bars or ovals, when present, and there is a hint of relation to the morphological type.
We present radio observations of the radio galaxy PKS 2152-699 obtained with the Australia Telescope Compact Array (ATCA). The much higher resolution and s/n of the new radio maps reveals the presence of a bright radio component about 10 arcsec NE of the nucleus. This lies close to the highly ionized cloud previously studied in the optical and here shown in a broadband red snapshot image with the HST PC2. It suggests that PKS 2152-699 may be a jet/cloud interaction similar to 3C277.3. This could cause the change in the position angle (of ~20 deg) of the radio emission from the inner to the outer regions. On the large scale, the source has Fanaroff & Riley type II morphology although the presence of the two hot-spots in the centres of the lobes is unusual. The northern lobe shows a particularly relaxed structure while the southern one has an edge-brightened, arc-like structure.
We present new BeppoSAX LECS, MECS, and PDS observations of five lobe-dominated, broad-line active galactic nuclei selected from the 2 Jy sample of southern radio sources. These include three radio quasars and two broad-line radio galaxies. ROSAT PSPC data, available for all the objects, are also used to better constrain the spectral shape in the soft X-ray band. The collected data cover the 0.1 - 10 keV energy range, reaching 40 keV for one source. Detailed spectral fitting shows that all sources have a flat hard X-ray spectrum with energy index alpha_x ~ 0.75 in the 2 - 10 keV energy range. This is a new result, which is at variance with the situation at lower energies where these sources exhibit steeper spectra. Spectral breaks ~0.5 at 1 - 2 keV characterize the overall X-ray spectra of our objects. The flat, high-energy slope is very similar to that displayed by flat-spectrum/core-dominated quasars, which suggests that the same emission mechanism (most likely inverse Compton) produces the hard X-ray spectra in both classes. Contrary to the optical evidence for some of our sources, no absorption above the Galactic value is found in our sample. Finally, a (weak) thermal component is also present at low energies in the two broad-line radio galaxies included in our study.
We present optical and radio images, and long-slit spectra of the radio galaxy PKS 1932-464 (z=0.230). Our main goal is to determine whether the observed properties of the extended emission line nebulosity in this object show evidence for interactions between the radio jet and the extended ionized gas, or whether they can be explained in terms of the illumination of the extended gas by the active nucleus. Although the data do not show compelling evidence for jet-cloud interactions, the existence of two well distinguished emitting line regions with very different kinematics and ionization levels suggests the presence of such interactions. The large-scale gas distribution is complex and suggests a gravitational interaction between the host galaxy of PKS 1932-464 and a nearby companiongalaxy. The detection of a broad Ha emission line in the nuclear spectrum of the object provides evidence that this object is a broad line radio galaxy (BLRG) rather than a narrow line radio galaxy (NLRG) as previously supposed.
We present the first results of BeppoSAX observations of a small sample of low brightness FRI radio galaxies. The flux of all the targets is consistent with a thermal spectrum, as due to the presence of hot intracluster gas or galactic corona. Moreover in three sources a non thermal absorbed spectrum can be present in the MECS spectrum at energies larger than 7 keV, while for a fourth object a high energy flux has been detected in the PDS instrument at energies larger than 15 keV. This component could be related to the inner AGN surrounded by an obscuring torus.
New radio continuum (8 GHz and 1.4 GHz) and HI 21 cm line observations of the Seyfert 2 galaxy IC 5063 (PKS 2048-572) were obtained with the Australia Telescope Compact Array (ATCA). The 8 GHz image reveals a linear triple structure (~4'', 1.5 kpc) oriented perpendicular to the optical polarization position angle. It is aligned with the inner dust lane and shows strong morphological association with the narrow emission line region (NLR). At 21 cm, very broad (~700 km/s) HI absorption is observed against the strong continuum source. This absorption is almost entirely blueshifted, indicating a fast net outflow, but a faint and narrow redshifted component is also present. In IC 5063 we see clear evidence for strong shocks resulting from the radio plasma-ISM interaction in the central few kpc. However, the energy flux in the radio plasma is an order of magnitude smaller than the energy emitted in emission lines. Thus, shocks are unlikely to account solely for the global ionization of the emission line region, particularly at large distances. The HI emission outlines a warped disk associated with the system of dust lanes some ~2' (~38 kpc) in radius. The lack of kinematically disturbed gas outside the central few kpc, coupled with the disk warp and close morphological connection of the inner dust lanes and the large-scale ionized gas, support the idea that the gas at large radii is photoionized by the central region, while shadowing effects are important in defining its X-shaped morphology. The kinematics of the ionized and of the neutral gas suggests the existence of a dark halo.
We present the soft X-ray (0.1--2.4 keV) properties of a complete sample of 88 southern radio sources derived from the Wall \& Peacock 2-Jy sample. It comprises 68 radio galaxies, 18 quasars and 2 BL Lac objects. Whereas both BL Lac objects and all but one quasar are detected in the {\it ROSAT} All-Sky Survey, the fraction of detected radio galaxies is only $\sim$ 60 per cent. For the undetected sources upper limits to the X-ray flux are given. We confirm the correlation of the soft X-ray luminosity (\lx) with the core radio luminosity (\lc) for galaxies as well as for quasars using partial correlation analysis, whereas the corresponding correlations between \lx and \lt are probably spurious due to sample selection effects. We also find strong correlations between \lx and \lc for both Fanaroff-Riley type I (FR~I) and type II galaxies. The broad-line radio galaxies (BLRGs) and the quasars are at the top end of the X-ray luminosity distribution and the detection rate of these objects generally is higher than that of the narrow- or weak-lined radio galaxies. This indicates the presence of an anisotropic X-ray component in BLRGs and quasars, as predicted by unified schemes for radio sources.