The B3-VLA CSS sample

Abstract

Context. Compact steep-spectrum radio sources and giga-hertz peaked spectrum radio sources (CSS/GPS) are generally considered to be mostly young radio sources. In recent years we studied at many wavelengths a sample of these objects selected from the B3-VLA catalog: the B3-VLA CSS sample. Only ≈60% of the sources were optically identified. Aims. We aim to increase the number of optical identifications and study the properties of the host galaxies of young radio sources. Methods. We cross-correlated the CSS B3-VLA sample with the Sloan Digital Sky Survey (SDSS), DR7, and complemented the SDSS photometry with available GALEX (DR 4/5 and 6) and near-IR data from UKIRT and 2MASS. Results. We obtained new identifications and photometric redshifts for eight faint galaxies and for one quasar and two quasar candidates. Overall we have 27 galaxies with SDSS photometry in five bands, for which we derived the ultraviolet-optical spectral energy distribution (UV-O-SED). We extended our investigation to additional CSS/GPS selected from the literature. Most of the galaxies show an excess of ultra-violet (UV) radiation compared with the UV-O-SED of local radio-quiet ellipticals. We found a strong dependence of the UV excess on redshift and analyzed it assuming that it is generated either from the nucleus (hidden quasar) or from a young stellar population (YSP). We also compare the UV-O-SEDs of our CSS/GPS sources with those of a selection of large size (LSO) powerful radio sources from the literature. Conclusions. If the major process of the UV excess is caused by a YSP, our conclusion is that it is the result of the merger process that also triggered the onset of the radio source with some time delay. We do not see evidence for a major contribution from a YSP triggered by the radio sources itself.

Multifrequency VLBA observations of two compact symmetric objects

“…The components in the source of the radio source. In 07101439 and 2352149 et al 1996b), it seems th radio jets and lobes on bo two-sided radio structures Conway et al (1990aConway et al ( , 19 (1994 and Readhead et a used by Readhead et al emission on both sides of symmetry between the tw radio galaxies are two-sid arm ratios, and flux densi This asymmetry may be d source with the ambient From (Stanghellini et al, 2001) and CSS (Fanti et al, 1995). Quasars are marked by crosses while galaxies are represented by squares.…”

“…(where the source growth is prevented by an anomalously dense Interstellar Medium of the host galaxy), or, in terms of Youth: the radio galaxy is small because young (Fanti et al, 1995) and it will develop and become larger and larger as it expands and ages. No evidence for a particularly dense medium has been found so far (Siemiginowska et al, 2005).…”

“…To solve this problem, evolutionary models which take into account changes in both the growth velocity and luminosity are required (Fanti et al, 1995). So far strong support to the youth scenario comes from both the determination of hot-spot separation velocity in a dozen of the most compact CSO (Polatidis, 2003), and the derivation of the radiative age from the analysis of the source spectra (Murgia 2003), showing that sources with sizes of about 100-500 pc are typically 10 3 years old.…”

“…In this Section I describe the model proposed by Fanti et al, (1995) based on a the properties of the selected sample of CSS/GPS presented (Fanti et al, 1995). First we assume that the source luminosity is constant.…”

Radio source evolution from galaxy core to intracluster medium

“…There is large overlap between these classifications in the sense that most CSOs are also GPS sources and that the MSO class contains the larger GPS objects and CSS objects. It is usually proposed that CSOs (GPS objects) evolve into MSOs (CSS objects), with the most powerful eventually becoming the classic FRIIs at large scales and the rest either shutting off completely or evolving into lower-luminosity, turbulent FRIs (e.g., Fanti et al 1995;Alexander 2000;Kunert-Bajraszewska & Labiano 2010). In this study we do not consider the duty cycle of CSOs, but rather model only those young sources that survive to become large-scale FRII sources.…”