In order to achieve the proper sample for study, we request three 24 hour sessions for observing with the VLBA at S/X bands of a complete sample of 500 sources in the zone delta > +75o with NVSS flux density > 200 mJy at 1.4 GHz regardless their spectral indexes. The VLBA results will be supplemented by instantaneous broad-band spectra measured in 2005 at RATAN--600 in the 2--22 GHz frequency range including S and X bands. This will allow direct comparison of the parsec scale structure and compactness versus the total flux density continuum spectra. We will propose VLBA follow-up observations for identified CSS at a later date in order to produce and analyze higher dynamic range mas-scale images than the once resulting from this search experiment.
Completeness of the sample and uniformity of the data reduction permits robust statistical analysis of this population of bright compact flat spectrum sources, such as: population modeling of the observed core brightness temperature in order to estimate distributions of the intrinsic core brightness temperature, the viewing angle, and Doppler brightening; expanding the cosmological significance of core-jet angular size versus redshift distribution, comparing the compactness of radio structures with IDV properties; correlating the radio core properties with optical class; etc.
However, the selection of candidates for the VLBA Calibrator surveys and the RDV programs was focused on observing the sources with a spectrum flatter than -0.5, which comprise approximately 15% of the entire population of radio sources at centimeter wavelengths. This spectral criterion guarantees that a large proportion of sources will be detected with mas-resolution. This spectral selectiveness is common for almost all previous VLBI surveys and future large VLBA surveys (e.g., VIPS, Taylor et al. 2005, to start in 2006). There are two exceptions, the PR+CJ1 and the Bologna samples.
The PR+CJ1 sample (e.g., Person & Readhead 1988, Xu et al. 1995) includes all sources with flux density > 0.7 Jy at 5 GHz. Unfortunately, only 128 out of 200 were observed with VLBI, so the sample of observed sources is complete only at the 64% level.
Another complete sample of sources, regardless of spectral index value, is the Bologna sample of 95 objects (Giovanni et al. 2004). However this sample, first, limits the objects with redshift z < 0.1, secondly, only a fraction of these objects has been observed with VLBI. Nevertheless, even preliminary results showed that statistics based on flat-spectrum samples may not give a valid role of compact emission in galaxies and quasars since they ``found a dramatically higher fraction of two-sided sources in comparison with that of previous flux-limited VLBI survey.'' We analyzed statistics of 3989 sources observed in 21 VLBA Calibrator survey experiments, 53 VLBA RDV experiments and 3941 Mark3/Mark4 experiments for geodesy and astrometry and compared it with the complete NVSS catalog (Condon et al. 1998). According to Table 1, only 20--30% of sources were observed even among the strong objects with the total flux density > 1 Jy at 1.4 GHz.
|S at 1.4 GHz, Jy||# total in NVSS||# observed||# detected|
The proposed observations will identify those sources from this sample which have compact details at the level of 20 mJy or higher at X and/or S bands. We expect that between 100 and 200 sources will be detected (this proportion is really unknown); images and positions at mas level will be obtained. Precise positions will enable performing reliable optical identification and follow-up VLBA studies which are planned for detected sources with mas-scale components.
Analysis of this sample should provide insight into the following questions:
List of 502 targeted sources in sched key format. The same list in NVSS format.
Pool of 122 sources which are suggested as tropospheric calibrators.
Pool of 10 sources which are suggested as amplitude calibrators.List of 27 sources scheduled as tropospheric and amplitude calibrators.
2006.02.16: bk130b is observed in [ 2006.02.16_08:03, 2006.02.17_08:07 ]
2006.02.14: bk130a is observed in [ 2006.02.14_03:19, 2006.02.15_03:17 ]
2006.02.08: The schedule files were submitted.
2005.09.30: Proposal was submitted to the Programme Committee on The code assigned: BK130
This page was prepared by Leonid Petrov
Last update: 2012.08.13_09:08:30