相关论文: Free-Free Absorption and the Unified Scheme

We report results of pentachromatic VLBI survey for 18 GHz-peaked spectrum sources. Spectral fitting at every pixel across five frequencies allows us to illustrate distribution of optical depth in terms of free-free absorption or…

We propose a morphological classification based on the parsec scale structure of fifty-one High Frequency Peakers (HFPs) from the ``bright'' HFP sample. VLBA images at two adjacent frequencies (chosen among 8.4, 15.3, 22.2 and 43.2 GHz)…

We observed 17 nearby low luminosity FR I radio galaxies using the NRAO Very Long Baseline Array (VLBA) at 1.67 GHz, as part of a multi-wavelength study of a complete sample of 21 sources selected by radio flux density from the Uppsala…

The VLBA and the VLA have been used to image the continuum radio emission from Mrk 231, a Seyfert 1 galaxy and the brightest infrared galaxy in the local universe. The smallest scales reveal a double source less than 2 pc in extent. The…

Seyfert galaxies come in two main types (types 1 and 2) and the difference is probably due to obscuration of the nucleus by a torus of dense molecular material. The inner edge of the torus is expected to be ionized by optical and…

In a long-term observing project we have imaged a complete sample of FRII quasars and radio galaxies with z < 1.0 at high resolution and high sensitivity with the VLA and MERLIN. This sample of 98 sources includes 15 quasars, 11 broad line…

We present Very Long Baseline Interferometry observations of a faint and low-luminosity ($L_{\rm 1.4 GHz} < 10^{27}~\mbox{W Hz}^{-1}$) Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sample. We select eight sources from…

We present VLBA observations at 15 GHz of ten GHz Peaked Spectrum (GPS) radio sources. The cores are often difficult or impossible to locate. When likely cores are found, they account for a small fraction of the flux density in GPS galaxies…

We have used the VLBA at 15 GHz to image the structure of 132 strong compact AGN and quasars with a resolution better than one milliarcsecond and a dynamic range typically exceeding 1000 to 1. These observations were made as part of a…

Global VLBI observations at 5 GHz have been performed to study the source morphology in 10 compact steep-spectrum (CSS) sources selected from the Peacock & Wall catalogue with the aim of finding asymmetric structures produced by the…

A sample of 123 radio sources that exhibit significant variations at 1.4 GHz on a seven year base-line has been created using FIRST VLA B-array data from 1995 and 2002 on a strip at dec=0 near the south Galactic cap. This sample spans the…

We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint Gigahertz Peaked Spectrum (GPS) sources selected from the Westerbork Northern Sky Survey (WENSS). The 5 GHz observations involved a global array…

The NRAO Very Long Baseline Array (VLBA) was used at 1.4 GHz to image 20 compact sources in the inner 1-degree radius of the Spitzer VLA First-Look Survey. Twelve sources were detected with the VLBA, with peak flux densities above 2 mJy at…

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…

We present high resolution (< 20 mas) observations of the radio continuum emission at 1.4 GHz from three high-redshift quasars: J1053-0016 (z=4.29), 1235-0003 (z=4.69), and J0913+5919 (z=5.11), thereby doubling the number of z > 4…

We have observed the canonical gigahertz-peaked spectrum source 0108+388 with the VLBA at a range of frequencies above and below the spectral peak. The activity that dominates the radio emission from 0108+388, which is also classified as a…

By modeling the broadband spectral energy distributions (SEDs) of a typical flat spectrum radio quasar (FSRQ, 3C 279) and two GeV narrow-line Seyfert 1 galaxies (NLS1s, PMN J0948+0022 and 1H 0323+342) in different flux stages with the…

We present the result of 27 ASCA observations of 26 radio-quiet quasars (RQQs) from the PG survey. All the RQQs were detected except 2 BALQSOs. We find the variability characteristics of the sources to be consistent with Seyf-1s. A powerlaw…

We have obtained mas-scale resolution very long baseline interferometry (VLBI) images of a sample of Seyfert 1 and Seyfert 2 galaxies at 5 GHz (wavelength, $\lambda$ = 6 cm). The Seyferts of the two types were chosen to be matched in…

This paper presents the first high-resolution and high-sensitivity study of the radio properties of optically selected type~2 quasars. We used the Very Large Array at 8.4 GHz to observe 59 sources drawn from the Sloan Digital Sky Survey…