December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 1

Microjansky Radio Sources:AGN or Star Formation?

Ken Kellermann & EdFomalontNRAO

in collaboration with

Neal Miller, Paolo Padovani, Vincenzo Mainieri, Paolo Tozzi

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 2

Star-formation, AGN, or ?• History of star and BH formation similar

– Does star formation trigger BH formation?– Do BH’s trigger star formation?– Is there a common underlying cause?– Jet feedback? + or -

• No single criteria to distinguish AGN & SF– UV/Optical observations

• Morphology, spectra• Obscuration

– FIR observations• Good tracer of star formation• Limited sensitivity/resolution

– X-ray observations• Good tracer of AGN• Weak x-ray emission from star formation

– Radio observations• AGN and SF detectable to large z• See through gas and dust• Morphology/Tb (resolution)• Spectra (α > -0.4 indicates AGN) (S α να)• Polarization, Variability• No redshift

Quasars

Star formation rate

Shaver et al., 1999

Hopkins & Beacon, 2007

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Chandra DeepField South

1 (2) Msec exposure366 X-ray sources5 x 10-17 ergs/sec

Extended CDFS250 ks per field

16 arcmin

Hubble UDF976 ks exposure

B, V, I, z10,000 galaxies

mag 29

GOODS ACSB, V, I, z < 28

GEMS/ACS, VLT/FORS ESO2.2m/WFI

VLA data (30% sensitivity level)

Spitzer – IRAC/MIPS

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 4

CDFS - 20 cm VLA image

266 radio sources in CD FS– σ = 8.5 μJy– S > 43 μJy– < 0.5 arcsec position accuracy

89 have X-ray counterparts

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 5

Optical/X-ray Counterparts in the VLA CDFS

254 O/IR counterparts– 10 Radio galaxies

– AGN + SFR

– 107 spectroscopic redshifts

– 79 photo z’s (17 bands)

– 12 Sources remain unidentified• 9 are ambiguous

• 3 no counterpart at any λ– OIR quiet

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 6

RID-97

R_WFI

R> 25.5 b> 27.5 v> 27.5

K> 24.4

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime

Radio Loud- 63%

R=log(Sr/So)

RL AGN

RQ AGN

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• Large scatter in μJy count

• Cosmic variance? NO!

• Instrumental errors– N(S) depends on instrument!

– incompleteness

– primary beam, bandwidth, time smearing corrections

– Statistical weight corrections

– Resolution corrections

Fomalont et al 2008ApJ S 179, 71

Padovani et al.ApJ submitted

Lx > 1042 W/HzR < 1.4

Star forming galaxies• R < 1.7• Lr< 1024.5 W/Hz• Not E galaxy• Lx not > 1042 ergs/sec

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 9

θ = 3.5 arcsec θ = 13.3 arcsec

Miller et al., unpublishedKellermann et al. ApJS, v179, 90

Chandra Deep Field South – VLA 20 cm: S > 55 μJy

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 10

Resolution vs. confusion

• Resolution < few asec to avoid confusion at 20 cm

• If the nanoJy population has dimensions of ∼ 1 arcsec, natural confusion may be a limiting factor

VLA+MERLINMuxlow et al.

MNRAS 358, 1159

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SummarySummary• Classification as SF or AGN

– Radio and X-ray Luminosity– Ratio radio/optical flux density– Optical morphology and spectra reaching faint magnitudes

• μJy radio population includes RQ and RL AGN and SFG• SF & BH probably co-exist• There is no “correct” resolution to use for EVLA deep surveys

– Good compromise ≈ 1 arcsec (35 km at 2.5 GHz)– 0.1 arcsec (300 km) to image sub-microJy sources (EVLA+eMERLIN)– 0.01 arcsec (3000 km) to distinguish between SF and AGN (VLBA +EVN)

• AGN: Tb > 105 for 1 μJy

• Issues for the EVLA and for design of the SKA– Determine the submicroJy source density - confusion– Angular structure – natural confusion? – The importance of cosmic variance– Optimum frequency for studying faint radio sources– Very high dynamic range (~ 105) needed if EVLA is to reach the thermal noise

limits in a few hundred hours• Primary beam• Pointing stability• Source spectra• Variability

December 17, 2008 The EVLA VisionGalaxies Through CosmicTime 12

CDFS/ECDFS• 20 & 6 cm CDFS

– I. Kellermann et al., ApJS , 179, 90 (CDFS – VLA)

•8 μ σ ∼ Jy, θ ~ 3.5 arsec

– II. Mainieri et al. ApJS, 179, 95 (CDFS – optical)

– III. X-ray sources, Tozzi et al. ApJ, (submitted)

– IV. Population Studies, Padovani et al. ApJ, in press

– V. Fomalont et al., 6 cm, σ ∼ 5 μJy, θ ~ 3.5 arcsec (in prep)

– VI. CDFS, Miller et al., 20 cm, σ ∼ 10 μJy, θ ~ 13 arcsec (in prep)

• 20 cm ECDF– Miller et al. ApJS, 179, 105

• σ ∼ 8 μJy, θ ~ 2 arcsec (S >55 μJy)

– Miller et al. , 20 cm, θ ~ 2 arcsec (in prep)

• σ ∼ 7 μJy, θ ~ 2 arcsec (S > 35 μJy)