118 research outputs found
X-ray Emitting GHz-Peaked Spectrum Galaxies: Testing a Dynamical-Radiative Model with Broad-Band Spectra
In a dynamical-radiative model we recently developed to describe the physics
of compact, GHz-Peaked-Spectrum (GPS) sources, the relativistic jets propagate
across the inner, kpc-sized region of the host galaxy, while the electron
population of the expanding lobes evolves and emits synchrotron and
inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the
expanding lobes, and photoionized by the active nucleus, are responsible for
the radio spectral turnover through free-free absorption (FFA) of the
synchrotron photons. The model provides a description of the evolution of the
spectral energy distribution (SED) of GPS sources with their expansion,
predicting significant and complex high-energy emission, from the X-ray to the
gamma-ray frequency domain. Here, we test this model with the broad-band SEDs
of a sample of eleven X-ray emitting GPS galaxies with Compact-Symmetric-Object
(CSO) morphology, and show that: (i) the shape of the radio continuum at
frequencies lower than the spectral turnover is indeed well accounted for by
the FFA mechanism; (ii) the observed X-ray spectra can be interpreted as
non-thermal radiation produced via IC scattering of the local radiation fields
off the lobe particles, providing a viable alternative to the thermal,
accretion-disk dominated scenario. We also show that the relation between the
hydrogen column densities derived from the X-ray (N_H) and radio (N_HI) data of
the sources is suggestive of a positive correlation, which, if confirmed by
future observations, would provide further support to our scenario of
high-energy emitting lobes.Comment: 29 pages, 3 figures, 6 tables; to appear in ApJ. A few clarifications
included, according to referee's suggestion
Multi-frequency VLBA study of the blazar S5 0716+714 during the active state in 2004: I. Inner jet kinematics
We observed the blazar \object{0716+714} with the
VLBA during its active state in 2003-2004. In this paper we discuss
multi-frequency analysis of the inner jet (first 1 mas) kinematics. The
unprecedentedly dense time sampling allows us to trace jet components without
misidentification and to calculate the component speeds with good accuracy. In
the smooth superluminal jet we were able to identify and track three components
over time moving outwards with relatively high apparent superluminal speeds
(8.5-19.4 ), which contradicts the hypothesis of a stationary oscillating
jet in this source. Component ejections occur at a relatively high rate (once
in two months), and they are accompanied by mm-continuum outbursts.
Superluminal jet components move along wiggling trajectories, which is an
indication of actual helical motion. Fast proper motion and rapid decay of the
components suggest that this source should be observed with the VLBI at a rate
of at least once in one or two months in order to trace superluminal jet
components without confusion.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letter, language
corrections adde
Mid-Infrared Diagnostics of the Circumnuclear Environments of the Youngest Radio Galaxies
We present a systematic analysis of the mid-infrared (MIR) properties of the
youngest radio galaxies, based on low-resolution data provided by the {\it
WISE} and {\it IRAS} satellites. We restrict our analysis to sources with
available X-ray data that constitute the earliest phase of radio galaxy
evolution, i.e. those classified as Gigahertz Peaked Spectrum (GPS) and/or
Compact Symmetric Objects (CSOs). In our sample of 29 objects, we find that the
host galaxies are predominantly red/yellow ellipticals, with some of them
displaying distorted morphology. We find a variety of MIR colors, and observe
that the sources in which the MIR emission is dominated by the ISM component
uniformly populate the region occupied by galaxies with a wide range of
pronounced (\,yr) star formation activity. We
compare the MIR color distribution in our sample to that in the general
population of local AGN, in the population of evolved FR\,II radio galaxies,
and also in the population of radio galaxies with recurrent jet activity. We
conclude that the triggering of radio jets in AGN does not differentiate
between elliptical hosts with substantially different fractions of young stars;
instead there is a relationship between the jet duty cycle and the ongoing star
formation. The distribution of the sub-sample of our sources with on
the low-resolution MIR vs. absorption-corrected X-ray luminosity plane is
consistent with the distribution of a sample of local AGN. Finally, we comment
on the star formation rates of the two -ray detected sources in our
sample, 1146+596 \& 1718--649.Comment: Revised version, accepted by the Astrophysical Journa
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