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A blind survey for compact HII regions at 20 GHz
Tara Murphy Ron Ekers, Martin Cohen, Anne Green

9th September 2010


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The Australia Telescope 20 GHz Survey (AT20G)
Covers southern sky ( < 0 ) S20 40 mJy Follow-up at 20, 8 and 5 GHz Carried out from 2004 to 2008 3000 hours of observing Main aims were: Population characterisation Spectral index distribution Variability studies Polarisation Extended sources Murphy et al., 2010, MNRAS, 402, 2403 Massardi et al., 2008, MNRAS, 384, 775
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Fast scanning: the survey mode
Wideband analogue correlator

(8 GHz bandwidth)
ATCA fast scanning capability

(15 deg min-1 )
3 antennas scan sky in bands of

10 - 15 in Dec.
Earth rotation covers RA Cover sky fast despite

2.4 FoV
Candidate sources extracted

from the raw data
Hancock 2010, PhD Thesis Hancock et al., 2010 in prep
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A typical image from the scanning survey

Tara Murphy

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Candidates were followed up in snapshot mode
Primary follow-up at 20 GHz

Resolution 10 - 15 arcsec Hybrid array: 80- 300 m
Low freq follow-up (within weeks)

secondary A 5 min block A 20 targets 40 sec each secondary A 5 min secondary B 5 min

LST -2 hr

5 and 8 GHz Resolution 10 - 20 arcsec
Stokes IQUV at all frequencies

secondary A 5 min block A 20 targets 40 sec each secondary A 5 min

LST +2 hr

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The final catalogue: 5890 sources with S20 > 40 mJy

Catalogue available on Vizier and from http://www.atnf.csiro.au/research/AT20G
Murphy et al. 2010, MNRAS, 402, 2403
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The AT20G Galactic plane
Galactic plane (|b | < 1.5 ) hasn't been followed up We have scan maps, with fluxes accurate to 20%

We have done a pilot follow-up on a small sample
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UCHII are signposts of massive star formation
Mostly detected from MIR colour-colour selection criteria Rising sp ectral index at radio frequencies

Tara Murphy

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9th September 2010


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Sample selection
AT20G Galactic plane region (|b | 1.5 ) Overlap with Molonglo Galactic Plane Survey ( < -30 ) Bright (S20 GHz 200 mJy)

= 263 sources
Compact (in AT20G and MGPS-2) Isolated (in AT20G and MGPS-2)
20 Inverted sp ectrum (0.843 0.1)

= 46 sources

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Our follow-up observations aimed to:
Measure accurate 20 GHz fluxes

= 18.624 GHz follow-up snapshot imaging Detect recombination lines to calculate size, Te = 18.769 GHz H70 recombination line detection Compare radio emission with MIR = 18.496 / 19.520 GHz high resolution imaging Characterise SEDs of objects = higher frequency (40, 100 GHz) imaging follow-up

Tara Murphy

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The UCHII SEDs show a 95 GHz excess

Tara Murphy

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Classification as UCHII or HCHII
Parameter Size Mean density Emission measure Recombination line width UCHII < 0.1 pc 104 cm-3 107 pc cm-6 40kms-1 HCHII < 0.05 pc 3в 105 cm-3 108 pc cm-6 > 40kms-1

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G302.0321-00.0606

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G301.1366-00.2248

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Summary
We have conducted the first blind radio survey for ultra and

hyper-compact HII regions.
We have found 33 HI I regions, of which at least 4 are UCHI I,

2 are HCHII and 2 are borderline.
We are currently monitoring several sources as potential high

frequency flux calibrators for the ATCA.
For more information: Murphy et al. 2010, MNRAS, 405, 1560

We welcome collaboration on this project or other ideas for

Galactic science with the AT20G data. http://www.atnf.csiro.au/research/AT20G

Tara Murphy

HCHII2010

9th September 2010