VLBA Calibrator Survey for reaching completness (VCS10)
Goals
The main goal of the project is to investigate the relationship between
compactness, spectral index at kiloparsec scale (angular size at
aresecond level), spectral index at parsec scale (angular size at
milliarcsecond level), source size and its morphology at parsec scales
from VLBA images and kiloparsec scales using VLA images from NVSS and
VLASS. The key scientific questions are
- Which parts of an AGN dominates in emission at different
frequencies and different resolutions?
- Can the spectral index be used as a discriminator of radio source
properties? If yes, which properties and what are the eliminations?
- How different the statistics of VLBI detected sources drawn from
flat-spectrum biased parent samples are different from the
statistics drawn from unbiased samples? How many compact sources
do we miss? For instance, CGRaBS catalogue of flat specrtum sources
was used by Fermi mission for associations
of γ-rays sources with AGNs. How many AGN associations were
missed due to the selection bias?
This will be achieved by the following way:
- We will produce images of proposed target sources at 4.3 and 7.6 GHz
and compute the total VLBA flux density, the median flux density at
baseline projections shorter 900 km, and the median flux density at
baseline projections longer 5,000 km. These flux density estimates
will augment information collected from dual-band images of other
sources of the sample that have been previously observed.
- We will determine the fraction of compact sources as a function of
spectrum among AGNs for each of three complete flux-limited samples,
the sample drawn from the NVSS at 1.4 GHz,
from the GB6+PMN at 4.85 GHz, and the sample draw from AT20G at 20 GHz.
These samples are complimentary to each other.
- We will analyze the physical differences between flat and steep spectrum
radio sources by correlating the flux density, angular size, and spectral
index of the compact component with single-dish total flux spectra of the
sources integrated over 10—100'' area. We have collected information
about single-dish flux densities and spectral indies of our samples from
literature and we will run RATAN—600 observations to collect missing
information for the rest of the target sources. We will also compute
spectral indices over 2—4 GHz from VLASS observations over entire source
and over the central pixels of VLASS images.
A by-product of this campaign will be a list of new calibrators near the ecliptic
plane that are used for space navigation and VLBI observations of interplanetary
spacecrafts. The newly detected sources from AT20G will be useful as ALMA
calibrators since they are brighter than 40 mJy at 20 GHz. We will determine
absolute positions of all detected sources with accuracies better 1 mas.
It is not practical to conduct an unbiased all sky survey. However,
it is within an arm reach to get a complete, unbiased flux limited sample
in two relatively large areas. First, a zone with ecliptic latitude
β ∈ [-7.5°, 7.5°]
was observed with the VLBI ecliptic
plane survey. The parent catalogue is GB6+PMN and the
detection limit of the survey was 13–18 mJy. By 2019 only 616 sources
brighter 70 mJy have not been not observed. Second, a zone with δ ∈
[-40°, 0°] was observed in a number of VLBI surveys with
a detection limit of 10–12 mJy. Only 742 sources from the AT20G catalogue
brighter 40 mJy have not been observed with VLBI. Among them, 8 sources
are in both list.
VLBA observations of missing 1350 sources will make two
unbiased flux-limited samples of over 2000 sources each.
Source count from prioir observations among
GB6+PMN sample |β| < 7.5° (targets are with flux @ 4.85 GHz > 70 mJy) and
AT20G sample -40° < δ < 0° (targets are with flux @ 20 GHz > 40 mJy):
| Sample | # Tot | # Obs | # Det | # Non-det | # Targets |
| GB6+PMN | 5756 | 5140 | 1958 | 3182 | 616 |
| AT20G | 3572 | 2830 | 2543 | 287 | 742 |
| Total | | | | | 1358 |
Results
The list of observed sources.
Status on 2020.02.16
| The total number of sources observed: | 1881 | |
| The number target sources observed: | 1751 | |
| The number of primary target sources observed: | 1350 | |
| The number of secondary sources observed: | 401 | |
| The number of calibrator sources observed: | 130 | |
| The number of segments observed: | 15 | |
| The number of segments correlated: | 15 | |
| The number of segments with preliminary solution: | 15 | |
| The number of segments imaged: | 15 | |
| The number images | 2420 | |
| The number of target sources detected at any band: | 1092 | |
| The number of target sources detected at C band: | 1079 | |
| The number of target sources detected at X band: | 1028 | |
| The number of target sources detected at both bands: | 1019 | |
| Detection rate: | 62% | |
| Nominal campaign duration: | 65 hours | |
| On source time: | 32 hours | |
The catalogue of positions of 1079 target sources from C-band observations:
vcs10_c.sou
The catalogue of positions of 1028 target sources from X-band observations:
vcs10_x.sou
The list of source that 623 were observed, but not detected at C-band
The list of source that 674 were observed, but not detected at X-band
2420 images of observed sources are available.
Statistics after 15 segments:
| Sample | # Tot | # Obs | # Det | # Non-det | # Remained |
| GB6+PMN | 5780 | 5758 | 2198 | 3560 | 22 |
| AT20G | 3580 | 3570 | 3288 | 282 | 10 |
| Total | | | | | 32 |
The list of 32 missed sources to observe.
Change Log
- 2020.02.16 Manual inspection and re-imaging of sources deteceted
in all BP242 segments is finished. Images of 2049 sources
are available.
- 2020.01.20 Automatic imaging all BP242 segments is finished
- 2019.12.12 Processed all segements BP242A through BP242O
- 2019.09.08 Processed segement BP242C through BP242I
- 2019.08.11 Project page created
- 2019.08.10 Processed segement BP242A and BP242B
- 2019.07.24 First segmetn BP242A is observed
- 2019.05.28 The project was approved by the NRAO Program
Committee.
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This web page was prepared by Leonid Petrov
(
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Last update: 2020.02.16_13:37:19