Presentation on theme: "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."— Presentation transcript:
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
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 )
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 -60 o to -70 o ) in 2002/3 Main survey began in 2004 (Dec -30 o to -50 o now complete)
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
Pilot study results: two populations Aitoff equal area projection of the confirmed sources, in Galactic coordinates Two populations: Galactic & extragalactic
Pilot study: source density Steep increase in source density near the Galactic plane Galactic sources: mainly HII regions, some young SNRs? Extragalactic sources: Mainly QSOs, blazars, radio galaxies (AGN)
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: > 90% for AT20G sources, < 30% for NVSS/SUMSS Most optical IDs are stellar (QSO candidates), many are `6dFGS additional targets’ (radio/X-ray sources) in DR1. SUMSS AT20G
Typical radio-galaxy SED Non-thermal (AGN) Thermal (stars + dust) 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
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
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)
Gamma-ray Sources with GLAST GLAST LAT (D. Thompson/GLAST team 2004) 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!!
AT20G sources in the 6dFGS DR1 1254 extragalactic (|b|>10 o ) radio sources detected at 20 GHz in declination zone -30 < < -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
Radio spectral index plots Radio spectral indices at low and high freq. uncorrelated (equivalent to a radio ‘two-colour diagram’)
Radio galaxy, main 6dFGS sample Powerful nearby radio galaxy (NGC3100) in main 6dFGS sample. 175 mJy at 20 GHz, 530 mJy at 1.4 GHz. 2MASS
QSO, z=3.12, radio additional target DSS BR Lyman Radio spectrum turns up above 8 GHz, 57 mJy at 20 GHz. Not selected in 6dF QSO samples
QSO, z=1.29, X-ray additional target DSS BR CIII MgII Radio spectrum peaks around 5 GHz, 350 mJy at 20 GHz.
BL Lac?, radio additional target BR 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 -ray blazar? Probably one of the strongest sources in the sky at 100 GHz?
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!!