Leonid Gurvits in collaboration with S.Frey, L.Mosoni, S.Garrington, M.Garrett, Z.Tsvetanov Joint VLBI in Europe Dwingeloo, The Netherlands

8-12 June 2003VLBA-10 Workshop, Socorro2 The challenge: to mine the terra incognita Need to observe mJy-level sources to study – W/Hz objects at z>0.5

8-12 June 2003VLBA-10 Workshop, Socorro3 Imaging VLBI surveys of extragalactic sources Pearson-Readhead and Caltech-Jodrell surveys: ~250 sources at 5 GHz: 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): 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):

8-12 June 2003VLBA-10 Workshop, Socorro4 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 ); 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 10 5 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 S 1.4 > 30 mJy (Note: NO spectral index criteria)  MERLIN detection of compact components brighter than ~2 mJy/beam

8-12 June 2003VLBA-10 Workshop, Socorro5 The sky area of DEVOS NGP (North Galactic Pole) The reference source: J VLBA Calibrator source 2°2° 2.3 GHz 8.4 GHz 47 FIRST/SDSS sources within 2° From J

8-12 June 2003VLBA-10 Workshop, Socorro6 DEVOS NGP – the sample of 47 sources FIRST data: 30 < S 1.4 < 490 mJy

8-12 June 2003VLBA-10 Workshop, Socorro7 MERLIN filter for DEVOS NGP Filter passed Observed at 5 GHz, 24 March 2001 J , 2 min NGP target, 4.5 min J , 2 min NGP target, 4.5 min Total: 15h 18m … + improved astrometry for VLBI φ-ref !

8-12 June 2003VLBA-10 Workshop, Socorro8 Global VLBI filter for DEVOS NGP Filter passed Observed at 5 GHz, 30 May 2001 J , 2 min NGP target, 2 min J , 2 min Total: 21 hr (7 hr global), min/target, 1σ thermal = 200 μJy/beam …

8-12 June 2003VLBA-10 Workshop, Socorro9 NGP01: VLBI detection at 4.4 mJy/beam

8-12 June 2003VLBA-10 Workshop, Socorro10 NGP14: 12.2 (MERLIN) and 2.2 (VLBI) mJy/beam

8-12 June 2003VLBA-10 Workshop, Socorro11 NGP15: 47 (MERLIN) and 20 (VLBI) mJy/beam

8-12 June 2003VLBA-10 Workshop, Socorro12 NGP32: 10 (MERLIN) and 7.9 (VLBI) mJy/beam

8-12 June 2003VLBA-10 Workshop, Socorro13 NGP36: 13.3 (MERLIN) and 1.4 (VLBI) mJy/beam

8-12 June 2003VLBA-10 Workshop, Socorro14 NGP47: 13.3 (MERLIN) and 13.5 (VLBI) mJy/beam

8-12 June 2003VLBA-10 Workshop, Socorro15 DEVOS NGP: the final yield 16/47 NGP sources detected with VLBI 30%

8-12 June 2003VLBA-10 Workshop, Socorro16 Conclusions: what to expect at the VLBA-20 Workshop DEVOS NGP produced 16 mJy-level VLBI detections in ~12 deg 2; Quarter of the sky (~10,000 deg 2 ) 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