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)

25 Nov 2009 5

““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)

25 Nov 2009 6

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

25 Nov 2009 7

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

25 Nov 2009 8

zSF

2SLAQ radio galaxies redder (and more clustered: Wake+ 08) than the general LRG population, passively-evolving optical LF.

25 Nov 2009 9

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

25 Nov 2009 12

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

25 Nov 2009 13

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

25 Nov 2009 14

Piggyback spectroscopy:

Spare fibres from AAT WiggleZ survey.

FIRST radio sources with i<20.5 mag, no colour selection. ~3000 spectra so far

25 Nov 2009 15

Wigglez radio galaxiesWigglez radio galaxiesLRGs

QSOs

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Wigglez radio galaxiesWigglez radio galaxies

25 Nov 2009 17

Wigglez radio galaxiesWigglez radio galaxies

25 Nov 2009 18

Wigglez radio galaxiesWigglez radio galaxies

25 Nov 2009 19

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

25 Nov 2009 21

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/

25 Nov 2009 23

AT20G, radio two-colour diagram: 65% QSOs & BL Lacs, 25% galaxies, 10% faint/blank.

25 Nov 2009 24

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.

25 Nov 2009 28