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