Triggering radio galaxies at 0
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25 Nov 2009 1
Triggering radio galaxies at 0<z<1Triggering radio galaxies at 0<z<1
Elaine M. Sadler
Luminosity functions and stellar populations
New spectroscopic samples at 0<z<1
High frequency: the AT20G survey
[with Russell Cannon, Scott Croom, Tom Mauch, Tara Murphy, Helen Johnston, Paul Hancock & the AT20G, 6dFGS, 2SLAQ, WiggleZ and GAMA survey teams]
25 Nov 2009 2
Radio-source populations at z~0Radio-source populations at z~0
Local radio-source populations now mapped out in detail from large-area radio + optical surveys
Good-quality optical spectra available for >20,000 local radio-emitting galaxies! (2dFGRS/SDSS/6dFGS +NVSS/SUMSS/FIRST)
25 Nov 2009 3
Local (z~0) radio LFs for AGN and star-forming galaxies now accurately measured over six orders of magnitude.
Sample is large enough to split by MK
SF
AGN
(Mauch & Sadler 2007) NVSS+6dFGS
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Fraction of galaxies hosting radio-loud AGN increases with galaxy stellar mass (Auriemma+ 77,
Sadler+ 89, Best+ 05)
BH duty cycle high in local massive galaxies
(Mauch & Sadler 2007)
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““Post-starburst” radio galaxiesPost-starburst” radio galaxies
2dFGRS radio galaxy: Balmer abs. lines imply a massive (~1010 Msun) starburst occurred ~0.15 Gyr ago. Compact, steep-spectrum radio source has P1.4 ~ 1025 W/Hz, MK ~ -25. Extremely rare locally! (<0.01% of radio AGN)
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Stellar populations of radio galaxies at Stellar populations of radio galaxies at 0.4<z<0.8 0.4<z<0.8
Photometric selection from SDSS, sky area ~150 deg2
• Optical spectra and redshifts from AAT/2dF
• 15,000 spectra of luminous red galaxies (LRGs) at 0.4<z<0.8
• 10,000+ faint QSO spectra
Survey paper: Cannon et al. (2006) MNRAS 372, 425
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First detection of cosmic evolution for low-power radio galaxies. P<1026 W/Hz radio AGN population well-fitted by luminosity evolution of the form (1+z)2. More rapid evolution for powerful sources (Sadler+ 07, Donoso+ 09)
z=0.5
z=0
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zSF
2SLAQ radio galaxies redder (and more clustered: Wake+ 08) than the general LRG population, passively-evolving optical LF.
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Composite LRG optical spectraComposite LRG optical spectra
0.45<z<0.50.55<z<0.65
Analysed matched composite spectra to test for differences between the stellar populations of radio-loud and radio-quiet 2SLAQ galaxies (Johnston+ 08).0.65<z<0.85
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Binned in redshift Binned in radio power
(Johnston+08)
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Fitted composite spectra with two single-age stellar populations, old (~7 Gyr) plus younger (10 Myr to 5 Gyr).
• In general, no difference between stellar populations of radio-detected galaxies and full 2SLAQ LRG sample.
• Around 30-40% of the light at 4000A comes from intermediate-age stars (~1 Gyr old, <1% by mass).
• The most powerful radio galaxies (>1026 W/Hz) have strong emission lines, AND a younger (100 Myr) stellar population.
Stellar populations at z~0.5Stellar populations at z~0.5
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L*
Recent mergers? Rapid evolution like ULIRGS, QSOs.
“Optically-quiet” radio galaxies Evolution as (1+z)2, similar to cosmic SF density. Not yet observed beyond z~0.7.
FRI
FRII
Represent ~ 0.5% of 2SLAQ galaxies at z~0.6
Cold mode?
Hot mode
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Blue radio galaxies at 0<z<1?Blue radio galaxies at 0<z<1?
• What about the effects of colour selection in LRG samples?
• Are we missing a population of blue radio galaxies?
• How are are radio galaxies and radio-loud QSOs related?
Work in progress: New spectroscopic survey, piggy-backed on AAT large-area WiggleZ and GAMA surveys
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Piggyback spectroscopy:
Spare fibres from AAT WiggleZ survey.
FIRST radio sources with i<20.5 mag, no colour selection. ~3000 spectra so far
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Wigglez radio galaxiesWigglez radio galaxiesLRGs
QSOs
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Wigglez radio galaxiesWigglez radio galaxies
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Wigglez radio galaxiesWigglez radio galaxies
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Wigglez radio galaxiesWigglez radio galaxies
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Currently ~3000 radio-loud AGN spectra from WiggleZ/GAMA, redshift range 0<z<1. Goal is to map out hot/cold accretion systems vs redshift and clustering environment to z~1.
25 Nov 2009 20Image Credit: D.Smyth
The Australia Telescope 20 GHz SurveyThe Australia Telescope 20 GHz Survey
2004-2009: Wide-band correlator on ATCA, 2.4 arcmin FoV, fast scanning at 15 deg/minute, 54ms sampling
AT20G team: PI Ron Ekers and 25 astronomers/engineers/students
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VLSS
WENSS
SUMSSNVSS
AT20GPMN
WMAP
Most work on radio galaxy populations/demographics has been at frequencies near 1.4 GHz - where the deepest radio surveys are. Can we learn something new at higher frequencies?
25 Nov 2009 22
Full AT20G source catalogue just released (Murphy et al. 2009)
Almost 6000 sources above 40 mJy limit, optical positions to ~1 arcsec.
Also simultaneous 5 and 8 GHz meas, polarization www.atnf.csiro.
au/research/AT20G/
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AT20G, radio two-colour diagram: 65% QSOs & BL Lacs, 25% galaxies, 10% faint/blank.
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O’Dea (1998) AT20G Sample
Typical Peak Freq 1 GHz 8-15 GHz
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 W/Hz 25 / 27 W/Hz
AT20G `extreme GPS’ sourcesAT20G `extreme GPS’ sources
Paul Hancock (2009 PhD thesis): Complete sample of 688 GigaHertz Peaked Spectrum (GPS) sources with spectral peaks above 5GHz - the youngest nearby radio sources?
25 Nov 2009 25
SUMSS 843 MHz
AT20G
AT20G J074618-570258: z=0.13, passive early-type galaxy. FRI Giant radio galaxy at 843 MHz (Saripalli+ 05), extreme GPS source with peak above 20 GHz (Hancock+ 09)
A nearby recently-retriggered radio galaxy?
25 Nov 2009 26
Local AT20G sources: the 6dFS sample
Complete spectroscopic sample, 195 sources with K<12.6 mag, median z~0.05.
~25% extended at 20GHz
Many `old friends’ from the 2Jy sample
Work in progress!
First measurement of the local (z<0.1) RLF at 20 GHz
25 Nov 2009 27
SummarySummary
• Luminosity functions are important - they tell us what’s common and what’s rare.
• High-frequency radio surveys are becoming easier, and can provide a new perspective on the demographics and triggering of young radio sources.
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