Leonid Gurvits in collaboration with S.Frey, L.Mosoni, S.Garrington, M.Garrett, Z.Tsvetanov
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Transcript of Leonid Gurvits in collaboration with S.Frey, L.Mosoni, S.Garrington, M.Garrett, Z.Tsvetanov
Leonid Gurvitsin collaboration with
S.Frey, L.Mosoni, S.Garrington, M.Garrett, Z.Tsvetanov
Joint VLBI in EuropeDwingeloo, The Netherlands
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The challenge: to mine the terra incognita
Need to observe mJy-level sources to study 1023 – 1025 W/Hz objects at z>0.5
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Imaging VLBI surveys of extragalactic sources
Pearson-Readhead and Caltech-Jodrell surveys: ~250 sources at 5 GHz:
www.astro.caltech.edu/~tjp/cj/
USNO VLBI survey at 2.3 and 8.4 GHz (Fey & Charlot, 1998):
rorf.usno.navy.mil/rrfid.html
VLBA Calibrator survey at 2.3 and 8.4 GHz (Peck & Beasley, 1998):
magnolia.nrao.edu/vlba_calib/index.html
VLBA-VSOP pre-launch survey at 5 GHz (Fomalont et al. 2000):
www.jive.nl/jive/jive/svlbi/vlbapls/
VSOP survey at 5 GHz (Fomalont et al. 2000):
oj287.vsop.isas.ac.jp/survey/
VLBA surveys at 15 GHz (Kellermann et al. 1998, Zensus et al. 2001,
Gurvits et al. 2003):
www.cv.nrao.edu/2cmsurvey/
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Deep Extragalactic VLBI-Optical Survey (DEVOS): the approach
To observe weak compact sources around bright ones using phase-referencing technique (Garrington, Garrett, Polatidis 1999 – he field around 1156+295);
To select targets using multi-step filtering: Overlay of optical and radio surveys; e.g. FIRST VLA and the Sloan
Digital Sky Survey (SDSS) can provide 105 targets MERLIN observations filter out sources too resolved for further VLBI
observations
DEVOS (Deep Extragalactic VLBI-Optical Survey) criteria: SLOAN-identified quasars (other types of AGN) identified as FIRST
sources with S1.4 > 30 mJy (Note: NO spectral index criteria)
MERLIN detection of compact components brighter than ~2 mJy/beam
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The sky area of DEVOS NGP (North Galactic Pole)
The reference source: J1257+3229VLBA Calibrator source
2°
2.3 GHz
8.4 GHz
47 FIRST/SDSS sources within 2°From J1257+3229
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DEVOS NGP – the sample of 47 sources
FIRST data:30 < S1.4 < 490 mJy
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MERLIN filter for DEVOS NGP
Filter passed
Observed at 5 GHz,24 March 2001
J1257+3229, 2 min
NGP target, 4.5 min
J1257+3229, 2 min
NGP target, 4.5 min
Total: 15h 18m
…
+ improved astrometry for VLBI φ-ref !
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Global VLBI filter for DEVOS NGP
Filter passed
Observed at 5 GHz,30 May 2001
J1257+3229, 2 min
NGP target, 2 min
NGP target, 2 min
J1257+3229, 2 min
Total: 21 hr (7 hr global), 12-14 min/target, 1σthermal = 200 μJy/beam
…
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NGP01: VLBI detection at 4.4 mJy/beam
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NGP14: 12.2 (MERLIN) and 2.2 (VLBI) mJy/beam
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NGP15: 47 (MERLIN) and 20 (VLBI) mJy/beam
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NGP32: 10 (MERLIN) and 7.9 (VLBI) mJy/beam
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NGP36: 13.3 (MERLIN) and 1.4 (VLBI) mJy/beam
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NGP47: 13.3 (MERLIN) and 13.5 (VLBI) mJy/beam
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DEVOS NGP: the final yield
16/47 NGP sourcesdetected with VLBI
30%
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Conclusions: what to expect at the VLBA-20 Workshop
DEVOS NGP produced 16 mJy-level VLBI detections in ~12 deg2;
Quarter of the sky (~10,000 deg2) would result in ~15,000 mJy-level detections!
Things to be sorted out:
Optimum “yield – filter threshold” relation At least one more pilot required (lower declination field, in
preparation) Observing and man-power resources
Higher recording data rate (e.g. 1 Gbit/s) reduces integration required Pipelining helps to keep post-docs alive and smiling
New instruments (“e”-Radio Astronomy) will make mJy-level VLBI surveys inevitable