I. A 22 GHz VLBI survey of 140 compact extragalactic radio sources. II. VLBA polarization observations of gamma-ray blazars at 15 and 22 GHz

A sample of 140 compact, flat- or inverted-spectrum extragalactic radio sources with $d\ge -40°$ and total flux density $Sn\gtrsim 1$ Jy has been observed with VLBI at 22 GHz on baselines of 4,400–10,800 km (3.3–8.0 × 108 λ) spanning the Pacific Ocean. Structural information on scales as small as ∼150 μas, in the form of brightness temperatures or lower limits, has been derived for the 136 sources that were detected. Twenty-one sources show evidence of structure with brightness temperature in the source frame greater than 1012 K.; Five γ-ray blazars have been observed with polarization-sensitivity at 15 and 22 GHz using the Very Long Baseline Array of the National Radio Astronomy Observatory in a search for detailed connections between milliarcsecond-scale jet direction and bending and the polarization structure. These sources provide a good test of such connections since their γ-ray emission implies jets aligned nearly along the line of sight and thus extreme projection effects should amplify even gentle bends. A number of distinctive total intensity properties are revealed by these observations, including broad jet opening angles, considerable diffuse emission despite high observing frequencies, a combination of sharply defined and diffuse jet boundaries, and narrow inner jets.; The most remarkable polarization features in these sources are the longitudinal magnetic fields inferred from the jet boundary polarization in at least three of the sources. This may indicate the stretching of otherwise random magnetic field at the interface between the jet and the surrounding medium which may explain the longitudinal field typically observed in quasars jets. In the interior of the jets, these sources tend to have transverse or oblique magnetic fields.