Abstracts

Abstracts for the talks at the workshop were totally optional. Any abstracts submitted are presented here and linked directly from the list of talks page.

III Zw 2: Evolution of a radio galaxy in a nutshell

Abstract: III~Zw~2 shows dramatic radio outbursts roughly every five years. Here we present the full set of lightcurves and VLBA observations of the latest flare with an excellent time sampling. We have discovered superluminal motion with a lower limit for the apparent expansion speed of $1.25\pm0.09$~c. Spectral and spatial evolution are closely linked. Before and after this rapid expansion we have seen a period ofvirtually no expansion with an expansion speed less than 0.04 c. However, at 15 GHz the picture is completely different. III~Zw~2 shows slow expansion ($\sim 0.6c$) during the time of no expansion at 43 GHz and no expansion during the rapid expansion at 43 GHz. The difference between the two frequency is qualitatively explained by optical depth effects in an 'inflating balloon-model', describing the evolution of radio lobes on an ultra-compact scale. The stop-and-go behavior could be explained by a jet interacting with a molecular cloud or the molecular torus. The unique and simple structure and timescales of such outbursts within 5 years makes III~Zw~2 an ideal source to study radio jet evolution relevant also to radio galaxies, especially those that appear as CSOs and GPSs. Since III~Zw~2 is also part of a sample of so called radio-intermediate quasars (RIQ), it confirms earlier predictions of superluminal motion for this source, based on the argument that RIQs could be relativistically boosted jets in radio-weak quasars and Seyfert galaxies.

High Frequency Peakers

Abstract: Extremely young radio sources should be very rare, and are likely to be found among those peaking at high frequencies. A brief overview of the properties of these High Frequency Peakers is given.

Optical/UV Spectral Signatures of GPS/CSS Sources

Abstract: The Cosmic Origins Spectrograph on the Hubble Telescope provides a unique chance to study GPS/CSS sources in the far-UV at a comparable spatial resolution to ground-based studies at longer wavelengths. I will show that this enables us for the first time to definitively identify the mode of excitation of the line emission, and to provide new observational constraints on the physical conditions in these sources.

A new test for the absorption mechanism of GPS using polarization properties

Abstract: We consider the use of polarization properties as a means to discriminate between Synchrotron Self-Absorption (SSA) and Free--Free Absorption (FFA) in GHz-Peaked Spectrum (GPS) sources. The polarization position angle (PA) of synchrotron radiation at high frequencies for the optically thin regime is perpendicular to the magnetic field, whereas it is parallel to the magnetic field at low frequencies for the optically thick regime. Therefore, SSA produces a change in PA of $90^{circ}$ across the spectral peak, while FFA does not result in such a change. We analyzed polarization data from VLA observations for six GPS sources to see if such a change in PA was present. Our results indicate that there is no significant evidence for $90^{circ}$ change in PA across the spectral peak, suggesting that FFA is more likely than SSA for low-frequency cutoffs in these sources. Based on the FFA model, we further discuss asymmetry in Faraday Rotation between lobes due to the difference of path length.

Dense Plasma Torus in the GPS Galaxy NGC 1052

Abstract: We report results from nearly simultaneous pentachromatic VLBI observations towards a nearby GPS galaxy NGC 1052. The observations at 1.6 and 4.8 GHz with VSOP, and 2.3, 8.4, and 15.4 GHz with VLBA, provide resolutions of ~0.1 pc. Convex spectra of the double-sided jet imply that synchrotron emission is obscured through the free--free absorption (FFA) by the foreground cold dense plasma. We found a central condensation of the plasma which covers about 0.1 pc and 0.7 pc of the approaching and receding jets, respectively. A simple explanation for the asymmetric distribution of FFA opacity is the existence of a geometrically thick plasma torus perpendicular to the jets.

Free-Free Absorption and the Unified Scheme

Abstract: We intend to study how commonly is free-free absorption (FFA) found around GPS sources. A multi-frequency survey for many GPS sources is needed to clarify the universality. We report observations of nine objects at 2.3, 8.4, and 15.4 GHz with the Very-Long-Baseline Array (VLBA) simultaneously. One Seyfert 1 galaxy, one Seyfert 2 galaxy, three radio galaxies, and four quasars were included in our survey. We obtained spatial distributions of the FFA opacity with milliarcsec resolutions for all sources. It is found that type-1 (Seyfert 1 and quasars) and type-2 (Seyfert 2 and radio galaxies) sources showed a significantly different distributions of the FFA opacities. The type-1 sources tend to show more asymmetric opacity distributions towards a double lobe, while those of the type-2 sources are rather symmetric. Our results imply that the different viewing angle of the jet causes the difference of FFA opacity along the external absorber. This idea supports the unified scheme between quasars and radio galaxies, proposed by Barthel (1989).

Two-sided radio jet in the CSS quasar B1524-1236

Abstract: We present MERLIN, global VLBI and VLBA observations of the high-luminosity, CSS quasar B1524-136 at cm wavelengths. These observations reveal well-defined radio jets on both sides of the active nucleus, a situation which is almost unique among high-luminosity radio quasars.

CSSs in a sample of B2 radio sources

Abstract: We present radio observations of 19 candidates CSSs object selected from a well-defined complete sample of 52 B2 radio sources of intermediate strength. These observations were made with the VLA A-array at 4835 MHz. The radio structures of the entire sample are summarised and the brightness asymmetries within the compact sources are compared with those of the more extended ones, as well as with those in the 3CRR sample and the CSSs from the B3-VLA sample.

The polarised gentle bent jet of 3C43

Abstract: We present VLBA 8.4 GHz images of the CSS quasar 3C43. The core of the source is clearly detected. The jet is imaged up to 200 mas from the core. It presents a very gentle bent. Polarised emission is detected along the jets and not detected in the core region as seen in others CSSs, a result which differs with the distribution of polarized emission found in core-dominated QSOs.

Search for CSS and GPS candidates from the Peacock and Well Catalogue

Abstract: A sample of sources from the PW Catalogue with unknown or uncertain mas structure has been observed with the VLBA at 1.6, 5, 8.4, 15 GHz. Our goal is to find among them small size CSS/GPS sources. These data will complete the structure knowledge of flat spectrum population of the PW sources. Preliminary results will be presented.

Population study of faint CSS radio sources: VLA-A observations at 74 MHz and their impact on evolution models

Abstract: Our observations consisted in a challenging experiment: using the 74-MHz receivers mounted on the VLA in A-configuration we determined the spectral turnover (peak frequency and peak flux-density) for a number of faint (S_wenss > 250 mJy) CSS radio sources. Combining the newly obtained information with information about the overall sourze size allows us either (1) to rule out or (2) to set further constraints on (much-loved) evolution models propagating the vision of self-similar growth of young radio sources. Be there when the outcome gets revealed.

Young radio galaxy

Abstract: We present preliminary results of new VLBA observations of a sample of sources peaking at frequencies higher than a few GHz, making them good candidates for being "newly born" sources. Our initial analysis deals with the morphological classification which allow to study the contamination from beamed sources dominated by a single unresolved component.

The shroud around the "compact, symmetric" radio jets in NGC1052.

Abstract: I will present and discuss multiple VLBA continuum and spectral imaging and WSRT spectroscopic observations of the compact variable nuclear radio source in NGC1052, which presents the appearance of a classical CSO. It consists of symmetric jets with sub-parsec scale features, propagating at near-relativistic velocities through or behind a complex medium, which is possibly the same as the optical broad-line emission region surrounding the nucleus of the galaxy. Absorption and emission signatures reveal ionised, atomic, and molecular components.

For more information, contact gpscss3@atnf.csiro.au

This page is maintained by Tasso Tzioumis.
Last Modified: 6 May 2002