The gravitational lens CLASS B1608+656 is one of the most promising lens systems for the measurement of H 0 on cosmological scales. The three independent time delays between the four lensed images have been measured, and the extended lensed optical emission holds the promise for a very well-constrained model. The published time delay measurements are based on the first season of VLA monitoring, in which the background source varied by only 5% in flux density. The small level of variation leads to relatively large uncertainties in the determination of the time delays (10-20%). Two more seasons of monitoring have now been completed and the source flux density has changed by ˜25% during that time. We present the results of the continued VLA monitoring and the resulting time-delay analysis. The new data have significantly reduced the uncertainties on the time delays and, hence, reduced the uncertainties on the resulting determination of H 0 from this system.
The four-component gravitational lens CLASS B1608+656 has been monitored with the VLA for two seasons in order to search for time delays between the components. These time delays can be combined with mass models of the lens system to yield a measurement of H_0. The component light curves show significantly different behavior in the two observing seasons. In the first season the light curves have maximum variations of ~5%, while in the second season the components experienced a nearly monotonic ~40% decrease in flux. We present the time delays derived from a joint analysis of the light curves from the two seasons.
The CERES Astronomical Archive was created initially in order to make the large amount of data that were collected from the two surveys, the Jodrell-VLA Astrometric Survey (JVAS) and the Cosmic Lens All-Sky Survey (CLASS), easily accessible to the partner members of the Consortium for European Research on Extragalactic Surveys (CERES) through the web. Here we describe the web based archive of the 15,000 flat spectrum radio sources. There is a wealth of information that one can access including downloading the raw and processed data for each of the sources. We also describe the search engines that were developed so that a) one can search through the archive for an object or a sample of objects by setting specific criteria and b) select new samples. Since new data are continually gathered on the same sources from follow up programs, an automatic update engine was created so that the new information and data can be added easily in the archive.
High-resolution Multi-Element Radio Linked Interferometer Network 5-GHz observations of seven Seyfert galaxies, selected as the ones previously showing evidence of collimated ejection, have been compared with high-resolution Hubble Space Telescope data. A radio and optical/near-ultraviolet emission correlation is apparent in all the sources. The radio maps reveal rich structures in the entire sample. NGC 2639 and TXFS 2226−184 have multiple-knot parsec-scale extended structures, Mrk 1034NED02, Mrk 1210, NGC 4922NED02 and NGC 5506 reveal one-sided jets, while IC 1481 exhibits jet features. Interaction between these very small (mostly mas) sub-kpc jets with dense material gives rise to symptoms of a disrupted medium, signatures of which are present in all the sources.
We present Very Large Array (VLA) 8.5-GHz light curves of the two lens images of the Cosmic Lens All Sky Survey (CLASS) gravitational lens B1600+434. We find a nearly linear decrease of 18-19% in the flux densities of both lens images over a period of eight months (February-October) in 1998. Additionally, the brightest image A shows modulations up to 11% peak-to-peak on scales of days to weeks over a large part of the observing period. Image B varies significantly less on this time scale. We conclude that most of the short-term variability in image A is not intrinsic source variability, but is most likely caused by microlensing in the lens galaxy. The alternative, scintillation by the ionized Galactic ISM, is shown to be implausible based on its strong opposite frequency dependent behavior compared with results from multi-frequency WSRT monitoring observations (Koopmans & de Bruyn 1999). From these VLA light curves we determine a median time delay between the lens images of 47^{+5}_{-6} d (68%) or 47^{+12}_{-9} d (95%). We use two different methods to derive the time delay; both give the same result within the errors. We estimate an additional systematic error between -8 and +7 d. If the mass distribution of lens galaxy can be described by an isothermal model (Koopmans, de Bruyn & Jackson 1998), this time delay would give a value for the Hubble parameter, H_0=57^{+14}_{-11} (95% statistical) ^{+26}_{-15} (systematic) km/s/Mpc (Omega_m=1 and Omega_Lambda=0). Similarly, the Modified-Hubble-Profile mass model would give H_0=74^{+18}_{-15} (95% statistical) ^{+22}_{-22} (systematic) km/s/Mpc. For Omega_m=0.3 and Omega_Lambda=0.7, these values increase by 5.4%. ... (ABRIDGED)
Using the final version of the VLA FIRST survey (Becker et al. 2003), the optical Sloan Digital Sky Survey Data Release 3 (DR3) quasar list and a series of carefully selected criteria, we have defined the largest homogeneous population of double‐lobed sources. With the precise sample definition, the increased depth and sensitivity of the survey data, the large size of the dataset, and our self‐consistent method of analysis, which addresses many of the problems associated with previous work in the area, we are able to: a) explore the correlations between the intrinsic properties of the double‐lobed radio sources (the results are also confirmed by a non‐parametric analysis) and study their evolution, b) place more interesting and tighter constraints on the cosmological parameters, distinguish among the different cosmology models, and determine the impact of the angular size‐redshift studies in cosmology, c) further our understanding of the behavior of the intergalactic medium (IGM) density as a function of redshift and shed more light to the quasar‐radio galaxy unification issue.
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