We describe the parsec-scale kinematics of 200 active galactic nucleus (AGN) jets based on 15GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 and 2011 May 1. We present new VLBA 15 GHz images of these and 59 additional AGNs from the MOJAVE and 2cm Survey programs. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12-16yr interval, ranging from 10{deg} to 150{deg} on the sky, corresponding to intrinsic variations of ~0.5{deg} to ~2{deg}. The BL Lac jets show smaller variations than quasars. Roughly half of the heavily observed jets show systematic position angle trends with time, and 20 show indications of oscillatory behavior. The time spans of the data sets are too short compared to the fitted periods (5-12yr), however, to reliably establish periodicity. The rapid changes and large jumps in position angle seen in many cases suggest that the superluminal AGN jet features occupy only a portion of the entire jet cross section and may be energized portions of thin instability structures within the jet. We have derived vector proper motions for 887 moving features in 200 jets having at least five VLBA epochs. For 557 well-sampled features, there are sufficient data to additionally study possible accelerations. We find that the moving features are generally non-ballistic, with 70% of the well-sampled features showing either significant accelerations or non-radial motions. Inward motions are rare (2% of all features), are slow (<0.1mas/yr), are more prevalent in BL Lac jets, and are typically found within 1mas of the unresolved core feature. There is a general trend of increasing apparent speed with distance down the jet for both radio galaxies and BL Lac objects. In most jets, the speeds of the features cluster around a characteristic value, yet there is a considerable dispersion in the distribution. Orientation variations within the jet cannot fully account for the dispersion, implying that the features have a range of Lorentz factor and/or pattern speed. Very slow pattern speed features are rare, comprising only 4% of the sample, and are more prevalent in radio galaxy and BL Lac jets. We confirm a previously reported upper envelope to the distribution of speed versus beamed luminosity for moving jet features. Below 10^26^W/Hz there is a fall-off in maximum speed with decreasing 15GHz radio luminosity. The general shape of the envelope implies that the most intrinsically powerful AGN jets have a wide range of Lorentz factors up to ~40, while intrinsically weak jets are only mildly relativistic.
We studied star formation activities in the molecular clouds in the Large Magellanic Cloud. We have utilized the second catalog of 272 molecular clouds obtained by NANTEN (4m radio telescope of Nagoya University at Las Campanas Observatory, Chile) to compare the cloud distribution with signatures of massive star formation including stellar clusters, and optical and radio HII regions. We find that the molecular clouds are classified into three types according to the activities of massive star formation: Type I shows no signature of massive star formation; Type II is associated with relatively small HII region(s); and Type III with both HII region(s) and young stellar cluster(s). The radio continuum sources were used to confirm that Type I giant molecular clouds (GMCs) do not host optically hidden HII regions. These signatures of massive star formation show a good spatial correlation with the molecular clouds in the sense that they are located within ~100pc of the molecular clouds.
In the article we present a rather extensive mapping survey of 19 molecular clouds in the SO(3_2_-2_1_) and CS(2-1) molecular lines and, at certain positions, also the corresponding 34S isotope lines. Here we present the maps of the survey.
We here analyse the observational SO and CS data presented in Nilsson et al. (2000A&AS..144..441N). The SO/CS integrated intensity ratio maps are presented for 19 molecular clouds, together with tables of relevant ratios at strategic positions, where w e have also observed ^34^SO and/or C^34^S.
The observations for the MDS1 were made in Sep. 1973 over a period of 16 days, and consist of drift scans with the telescope set to one declination number (-20 and -62{deg}) during the transit of the RA range of the survey, and scanning a long narrow strip of sky. The MDS2 results from observations made in 1978 with the same telescope working at its maximum sensitivity
The Molonglo Reference Catalog of Radio Sources results from a 408-MHz survey observations made with the Molonglo Radio Telescope (Australia) between 1968 and 1978. The survey covers 7.85sr of the sky between the declinations -85{deg} and +18{deg}, excluding the strip of the galactic plane (|b|<=3{deg}). The nominal beamwidth is 2.62arcmin in right ascension and 2.86sec({delta}+35.5)arcmin in declination. There are 7347 sources with flux density S>=1Jy, at which level the catalogue is substantially complete. A new version of the catalog has been done in 1990 (Cat. VIII/16).
"408-MHz survey observations made with the Molonglo Radio Telescope have been used to prepare a catalogue of 12 141 discrete sources of listed flux density >= 0.7 Jy. The survey covers 7.85 sr of the sky defined by +18.5 (deg) >= dec(1950) >= -85.0 (deg), mod(b) >= 3 (deg). A few sources beyond the declination limits are also included. The catalogue comprises celestial coordinates with standard error typically lying between 3 and 10 arcsec and 408-MHz flux densities with standard error typically lying between 4 and 10 per cent. Galactic coordinates, notes on source morphology and cross-references to the Parkes Catalogues are included. The overall source density is 1500/sr, corresponding to 0.001 per beam area. There are 7347 sources of listed flux density >= 1.00 Jy, at which level the catalogue is substantially complete. The reliability is believed to be better than 99.9 per cent." The MRC was re-issued in 1990 with the original B1950 coordinates supplemented by J2000 values, and an additional cross-reference flag `J' added to denote (extended) sources imaged at 843-MHz by P.A. Jones. No other alterations were made to the original release. The MRC is now available on 5.25 inch, 1.2 Mbyte MS-DOS (IBM) floppy disk (0.5 inch magnetic tape is also available, but is not the preferred medium). In the floppy disk format, simple software is provided to facilitate use of the catalogue on a PC computer.
We present light curves for 149 sources monitored with the Green Bank Interferometer. The light curves are at two radio frequencies (approximately 2.5 and 8.2GHz) and range from 3 to 15yr in length, covering the interval 1979-1996, and have a typical sampling of one flux density measurement every 2 days. Observations were made on a 2.4km baseline. Dual circular polarization was recorded over a 35MHz bandwidth at two frequencies in the S and X frequency bands. Until 1989 August (1989.7), the frequencies were 2.7GHz (S band) and 8.1GHz (X band); in 1989 September cryogenic receivers were installed, and the frequencies changed to 2.25GHz (S band) and 8.3GHz (X band).
High-resolution radio observations are ideal for constraining the value of physical parameters in the inner regions of active-galactic-nucleus jets and complement results on multiwavelength (MWL) observations. This study is part of a wider multifrequency campaign targeting the nearby TeV blazar Markarian 421 (z=0.031), with observations in the sub-mm (SMA), optical/IR (GASP), UV/X-ray (Swift, RXTE, MAXI), and {gamma} rays (Fermi-LAT, MAGIC, VERITAS). We investigate the jet's morphology and any proper motions, and the time evolution of physical parameters such as flux densities and spectral index. The aim of our wider multifrequency campaign is to try to shed light on questions such as the nature of the radiating particles, the connection between the radio and {gamma}-ray emission, the location of the emitting regions and the origin of the flux variability.
We investigate the optical morphologies of candidate active galaxies identified at radio, X-ray, and mid-infrared wavelengths. We use the Advanced Camera for Surveys General Catalog (ACS-GC) to identify 372, 1360, and 1238 active galactic nucleus (AGN) host galaxies from Very Large Array, XMM-Newton, and Spitzer Space Telescope observations of the COSMOS field, respectively. We investigate both quantitative (GALFIT) and qualitative (visual) morphologies of these AGN host galaxies, split by brightness in their selection band.
