high-frequency gps sources from the at20g survey

High-Frequency GPS sources from the AT20G

surveyPaul Hancock - University of Sydney

Australia

Ron Ekers (ATNF, PI), Sarah Burke(Swinburne), Mark Calabretta (ATNF), Gianfranco De Zotti (Padua), Paul Hancock (U Sydney), Carole Jackson (ATNF),

Michael Kesteven (ATNF), Marcella Massardi (SISSA/ATNF), Tara Murphy (U Sydney), Katherine Newton-McGee (U Sydney), Chris Phillips (ATNF), Roberto

Ricci (ATNF), Elaine Sadler (U Sydney), Lister Staveley-Smith (UWA), Mark Walker (MAW Tech), Jasper Wall (UBC),

Warwick Wilson (ATNF)

Outline

• Motivation• Technology• Observing strategy• Catalog Content

• GPS candidates• e-VLBI• Data release• Final words

Motivation for the AT20G survey

• No sensitive large area surveys above 5GHz

• Observation timedrastically reducedby using newhardware

• Provide foregroundsubtraction forCMB missions

• Study high frequency source populations including high frequency GPS

Image from Sadler et. al. - 2008MNRAS.385.1656S

WBAC

• 8GHz bandwidth• 16 Channels• 3 baselines• 54ms sampling rate• Simultaneous analog

correlation• No delay tracking

• 3 Telescopes• 15°min-1 scan rate• Observing at 20GHz• Optic fiber data

transport

ATCA

Image Credit: D.Smyth

Observing Strategy

• Delay tracking fixed on the meridian

• Telescopes scan N-S • Sky rotates E-W• Result is interleaving

tracks across the sky• Interleaves are stitched

together to form maps

Candidate Sources

• Resulting maps still show a beam response, rms noise ~10mJy

• Candidates are selected above 40mJy

Confirmation

• Imaging observations at 20GHz to measure accurate flux/positiono >80% confirmed as real sources

• Confirmed sources also observed at 5 and 8 GHz• Sky coverage -90\deg < DEC < 0\deg• Catalog contains 5700 sources above 40mJy at

20GHz

AT20G 0054-3418

AT20G Catalog Content

• ~4000 sources have nearly simultaneous measurements

• Almost all extragalactic sources are AGN:• 65% QSOs & BL Lacs• 25% galaxies• 10% faint/blank

• Nearly all are unresolved at 20GHz (<5’’)

• ~20% are GPS candidates (peaked or inverted)

11%

53%

13%

22%

Inverted

PeakedSteep

Upturned

GPS Sample

• Selected to be peaked or inverted at 20GHz• Avoided Galactic sources |b| < 2.5• 843MHz from SUMSS• 1.4GHz from NVSS• 20 inverted sources observed at 40GHz and 95GHz

with ATCA• 106 Redshifts from 6dF, NED• 38 Spectra observed at Siding Spring 2.3m telescope• 10 VLBI observations

•688 GPS sources with peaks above 5GHz

Z=0.066

Z=0.11

Z=0.60

Resulting Sources

Comparison to previous samples

O’Dea Sample AT20G Sample

Typical Peak 1GHz 8-15GHz

Number of sources

31 688

Galaxy/QSO fraction

50 / 50 23 / 77

Median Z 0.5 / 1.6 0.2 / 1.2

Median Log(P5) 27 / 28 25 / 27

O’Dea 1998 PASP, 110,493-532

e-VLBI

AT20G Data Release

• Sources above 500mJy are within the Bright Source Sample

• Full sample release is currently in preparation

• Website: www.atnf.csiro.au/research/AT20G/

• First results from the ATCA 18GHz pilot survey,    Ricci et al. 2004, MNRAS, 354, 305

• The properties of extragalactic radio sources selected at 20GHz,    Sadler et al. 2006 MNRAS 371, 898-914

• The Australia Telescope 20 GHz (AT20G) Survey: The Bright Source Sample Massardi et al. 2008, MNRAS, 384, 774-802

• The extragalactic radio-source population at 95GHz, Sadler et al. 2008 MNRAS 385, 1656

Conclusion / Final Words

• When the full sample release is complete it will open up a lot of new opportunities to study GPS (and CSS) sources

• 688 sources• 144 redshifts• 10 e-VLBI observations

• Future work:• More redshifts• More / Higher resolution e-VLBI measurements• Better radio spectra