VSOP space VLBI and geodetic VLBI investigations of southern hemisphere radio sources
Tingay, SJ and Reynolds, JE and Tzioumis, AK and Jauncey, DL and Lovell, JEJ and Dodson, R and Costa, ME and McCulloch, PM and Edwards, PG and Hirabayashi, H and Murphy, DW and Preston, RA and Piner, BG and Nicolson, GD and Quick, JFH and Kobayashi, H and Shibata, KM, VSOP space VLBI and geodetic VLBI investigations of southern hemisphere radio sources, The Astrophysical Journal Supplement Series, 141, (2) pp. 311-335. ISSN 0067-0049 (2002) [Refereed Article]
We present images from VLBI Space Observatory Programme (VSOP) observations of 14 compact extra-galactic southern hemisphere radio sources, including a description of the observations, the data reduction techniques, and the parameters of the resulting images and model fits. These images provide the highest resolution information to date for many of these objects. Comparisons are made between VSOP and previous ground-based VLBI results, including images from data extracted from the geodetic VLBI archive at the United States Naval Observatory. From the VSOP data, we find that the two radio galaxies observed have lower peak brightness temperatures than the 12 quasars. Also, these data show (1) no evidence for obvious differences between the brightness temperature distributions of gamma-ray-loud and gamma-ray-quiet radio-loud active galactic nuclei and (2) no evidence for obvious correlations between brightness temperature and spectral index, radio polarization, flux density, or month timescale modulation index. These results are consistent with previous work by Lister, Tingay, & Preston, who found that the only observable significantly correlated with VSOP-derived brightness temperature is intraday variability, which is strongly correlated with many relativistic beaming indicators. For one source, PKS 1127-145, we undertake a detailed investigation of the milliarcsecond-scale component positions as a function of time, taking data from the literature and the current work, to estimate proper motions. As a result, we suggest that two components previously reported as stationary, C1 and C2, have apparent transverse speeds of (9.1 ± 3.8) and (5.3 ± 2.3) h -1c, respectively. We also make the first investigation of the apparent motion in the nearest GHz-peaked spectrum radio galaxy, PKS 1718-649, finding an upper limit on the apparent separation speed of 0.08c. Comparison of geodetic VLBI and VSOP data show no significant detection of component motion in PKS 0208-512, (2.4 ± 3.1) h -1c, and only a tentative detection in PKS 0537-441, (2.8 ± 2.2) h -1c. A significant detection of component motion is found in PKS 1610-771, solely from the geodetic VLBI data, (9.4 ± 3.5) h -1c.