6dFGS spectra of radio sources at 20 and 100 GHz 12 and 3mm

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6dFGS spectra of radio sources at 20 and 100 GHz
(12 and 3mm)
Elaine M. Sadler (University of Sydney)

• The AT20G survey - first all-sky radio
  continuum survey at millimetre wavelengths
• The radio-source population at 12mm (QSOs,
  blazars and young radio galaxies)
• 6dFGS spectra of AT20G sources, and links to
  GLAST

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The AT 20 GHz Survey Team R. Ekers (PI), L.
Staveley-Smith, W. Wilson, M. Kesteven, R.
Ricci, R. Subrahmanyan , C. Jackson (ATNF) , E.
Sadler, M. Walker (Sydney), G. De Zotti (Padua)

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AT20G observing strategy

• 3 ATCA baselines (30, 30, 60m)
• Wide-band analogue correlator
• - frequency range 16-24 GHz
• - Bandwidth 8 GHz
• Active scanning, high scan rate 10 deg/min
• No delay correction, need to scan along meridian
• Detection limit 40 mJy at 20 GHz
• Pilot study (Dec -60o to -70o) in 2002/3
• Main survey began in 2004 (Dec -30o to -50o now
  complete)

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AT20G science goals

• First all-sky radio survey at mm wavelengths -
  investigate source populations at 20-100 GHz (not
  predictable from 1-5 GHz surveys!)
• Catalogue foreground discrete-source population
  for future CMB missions (variability,
  polarization particularly important).
• Set up new calibration network for ATCA, ALMA at
  20-100 GHz

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Pilot study results two populations
Aitoff equal area projection of the confirmed
sources, in Galactic coordinates Two populations
Galactic extragalactic
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Pilot study source density
Galactic sources mainly HII regions, some young
SNRs? Extragalactic sources Mainly QSOs,
blazars, radio galaxies (AGN)

• Steep increase in source density near the
  Galactic plane

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Optical IDs of AT20G sources

AT20G detects only a small subset of the
low-frequency (NVSS/ SUMSS) radio sources
discussed by Tom Mauch. High DSS optical ID
rate gt 90 for AT20G sources, lt 30 for
NVSS/SUMSS Most optical IDs are stellar (QSO
candidates), many are 6dFGS additional targets
(radio/X-ray sources) in DR1.
SUMSS
AT20G
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Typical radio-galaxy SED
Radio flux density decreases with increasing
freq. As a result, surface density of classical
radio galaxies (and starburst galaxies) is high
below 1 GHz, low above 10 GHz
Thermal (stars dust)
Non-thermal (AGN)
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Spectral-energy distribution of blazars
Blazars (BL Lacs and flat-spectrum radio QSOs)
have a characteristic double-peaked
SED Synchrotron peak anywhere in IR to X-ray
region. Inverse Compton scattering gamma- ray
peak (GeV to TeV energies)
(Ulrich et al. 1997)
Because of their rising radio spectra, blazars
are bright at 20 GHz
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Radio emission from blazars
Radio-loud AGNs (radio galaxies, quasars, BL
Lacs) have radio jets (pc scales) and/or lobes.
Blazar BL Lac Objects Flat-spectrum radio
QSOs (FSRQs) In unified model for AGNs,
blazars are viewed within about 20 of jet axis
(I.e. relativistic beaming common)
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Gamma-ray Sources with GLAST
GLAST Next-generation ?-ray satellite
due for launch in 2007. All-sky surveys will
probe 30x fainter than EGRET. Source
population expected to be blazars and pulsars
Southern blazar census AT20G 6dFGS!!
(D. Thompson/GLAST team 2004)
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AT20G sources in the 6dFGS DR1

• 1254 extragalactic (bgt10o) radio sources
  detected at 20 GHz in declination zone -30 lt d lt
  -50 deg.
• 62 of these (2.5) have 6dFGS spectra in DR1
  (which had incomplete coverage of the AT20G area)
• 26 galaxies in main 6dFGS sample (23 with
  redshifts)
• 34 additional targets 20 QSOs
• 5 BL
  Lacs
• 2
  emission-line galaxies
• 7
  with noisy spectra

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Radio spectral index plots
(equivalent to a radio two-colour diagram)
Radio spectral indices at low and high freq.
uncorrelated
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Radio galaxy, main 6dFGS sample
2MASS
Powerful nearby radio galaxy (NGC3100) in main
6dFGS sample. 175 mJy at 20 GHz, 530 mJy at 1.4
GHz.
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QSO, z3.12, radio additional target
DSS B
R
Radio spectrum turns up above 8 GHz, 57 mJy at 20
GHz. Not selected in 6dF QSO samples
Lyman a
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QSO, z1.29, X-ray additional target
DSS B
R
CIII
MgII
Radio spectrum peaks around 5 GHz, 350 mJy at 20
GHz.
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BL Lac?, radio additional target
B
R
Inverted radio spectrum, rising from 160 mJy at
1.4 GHz to 655 mJy at 20 GHz.
Detected by WMAP, 2.4 Jy at 4.9 mm, i.e. spectrum
continues to rise above 60 GHz! Likely g-ray
blazar? Probably one of the strongest sources in
the sky at 100 GHz?
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Summary

• 6dFGS (main-survey and additional-target
  samples) overlaps the AT20G radio survey and is
  useful in characterising high-frequency radio
  sources and measuring their redshifts.
• Could make the 6dFGS data even more useful by
• - allocating higher priority to AT20G additional
  targets (which have low surface density)
• adding a QSO template to the redshifting program
  to remove the need for re-redshifting QSO/blazar
  spectra
• Looking forward to DR2!!