RADIO OBSERVATIONS IN VVDS FIELD : PAST - PRESENT - FUTURE P.Ciliegi(OABo), Marco Bondi (IRA) G. Zamorani(OABo), S. Bardelli (OABo) + VVDS-VLA collaboration

The contribution of radio observations for multi-λ surveys Easier to image “large” regions of sky at freq < 2 GHz with arcsecond resolution.  FOV: VLA(1.4 GHz)= 30' GMRT(0.61 GHz)= 43'

The contribution of radio observations for multi-λ surveys Easier to image “large” regions of sky at freq < 2 GHz with arcsecond resolution.  FOV: VLA(1.4 GHz)= 30' GMRT(0.61 GHz)= 43' Radio emission is not affected by dust obscuration and gas extinction:  Ideal to derive the Star Formation History  Find highly obscured classes of AGNs or SB  Test the FIR/radio correlation at high redshift

The contribution of radio observations for multi-λ surveys Easier to image “large” regions of sky at freq < 2 GHz with arcsecond resolution.  FOV: VLA(1.4 GHz)= 30' GMRT(0.61 GHz)= 43' Radio emission is not affected by dust obscuration and gas extinction:  Ideal to derive the Star Formation History  Find highly obscured classes of AGNs or SB  Test the FIR/radio correlation at high redshift Other more general goals:  Sub-mJy source counts  Evolution of the currently highly uncertain faint-end of the radio luminosity function

The limitation of radio observations for multi-λ surveys Not possible for radio emission alone to determine redshift or even distinguish between AGNs and galaxies

The limitation of radio observations for multi-λ surveys Not possible for radio emission alone to determine redshift or even distinguish between AGNs and galaxies  Photometric redshift using radio band: Radio-to-submm spectral index (Carilli & Yun 1999) Radio-to-FIR SED (Yun & Carilli 2002)  Resolution filter: pc-scale resolution observations to pinpoint the radio AGN and disentangle it from the extended emission (e.g. Garrett et al. 2001, Garrett et al. 2005)

The limitation of radio observations for multi-λ surveys Not possible for radio emission alone to determine redshift or even distinguish between AGNs and galaxies  Photometric redshift using radio band: Radio-to-submm spectral index (Carilli & Yun 1999) Radio-to-FIR SED (Yun & Carilli 2002)  Resolution filter: pc-scale resolution observations to pinpoint the radio AGN and disentangle it from the extended emission (e.g. Garrett et al. 2001, Garrett et al. 2005) Only a small fractions of optical objects (AGNs and galaxies) are radio-loud  Radio stacking analysis to derive the median radio properties of a radio-quiet population selected at a different band (Georgakakis et al. 06, Simpson et al. 06, White et al. 07, Garn & Alexander 08)

VVDS Radio Survey (Bondi et al. 2003, 2007; Ciliegi et al. 2005; Bardelli et al. 2009) Carried out with the VLA at 1.4 GHz and GMRT at 0.6 GHz Survey area: 1 square degree Catalog of about 1100 radio sources down to flux limit 0.1 mJy The whole area was followed up by multicolor optical and NIR imaging plus optical spectroscopy Aimed at obtaining the radio source counts down to 0.1 mJy and the radio spectral properties of the sub-mJy population.

Results: Radio Source Counts First interpretation of change in the slope of sub-mJy counts was an evolving population of starbursts. Now it is clear that a mixing of different populations is responsible for the flattening AGN and starburst contribution to the sub-mJy population Bondi et al. 2003

Results: Radio Source Counts Wide scatter of source counts below 1 mJy from different surveys (cosmic variance & incompleteness corrections) Bondi et al. 08

Results: OPTICAL ID Seymour et al. 09 Ciliegi et al. 2005

VIRMOS F Ghz Bondi et al. '03 Ciliegi et al. '05

VIRMOS F Ghz Bondi et al. '06

VVDS GMRT RADIO SURVEY The deepest and largest survey at 610 Mhz so far (rms ~ 50 microJy/beam) The largest sample of sub-mJy sources for spectral index studies: 741 (652 sub-mJy) spectral index values limits 75% of the sample optically identified (colors, morphological type & z phot) Bondi et al 2007

Evidences of different populations at the sub-mJy level. Median spectal index ( mJy) flatter than that brighter sources. Contribution from AGN and radio quiet QSO. The contribution of starburst become important below 0.2 mJy VVDS GMRT 0.6 GHz Sample of 58 candidate ultra-steep sources. High z sources ? 35% of USS source with S(1.4GHz) > 10 mJy have z > 3 (De Breuck et al. 2000)

Red 0<z<0.7 Black 0.7<z<1.0 LUMINOSITY FUNCTIONS Type 1+2 (early) LF=  0 (1+z) k (L/L*)  Early: increase of radio-optical ratio compensated by decrease of optical luminosity function Bardelli et al. 2009

Red 0<z<0.5 Black 0.5<z<1.1 Type 3+4 (late) LUMINOSITY FUNCTIONS LF=  0 (1+z) k (L/L*)  where L=L 0 (1+z)   =  = 2.63 K= 0.43

SFR(radio)=SFR(optical) line 30% of objects below “equality line” (i.e. > ) ==> effect of dust? SFR(radio) vs SFR(optical)

Log (sfrVVDS)- Log (SFRradio)= +/ Expected 0.74 From FUV (1500Å) (Hopkins et al 2001) SFR density  (1+z) 2.15 Uncorrected SFR form FUV (Tresse et al. 2007)

LF CONCLUSIONS Radio Luminosity Functions evolution Early: increase of radio-optical ratio compensated by decrease of optical luminosity function Late : one magnitude evolution of optical population, no Evolution of radio-optical ratio SFR(radio> > (dust) Possible to use optical galaxies as tracers for radio emission in particular for the estimation of the Star Formation History

PRESENT AND FUTURE Radio properties of non-radio detected objects Only a small fraction of optical galaxies are radio detected. Stacking techniques can be used to derive the average radio properties of a large population of sub-threshold objects selected in a different band (optical, IR, X-rays...). Stacking N objects the noise in the stacked image can decrease by square root of N. Applied to 1 ) a sample of about 900 Extremely Red Objects 2 ) a mass limited sample of 4420 VVDS objects 0.15 < z < 1.2

The radio properties of EROs Starting from the K-band selected photometric sample, obtained 898 objects with K(Vega) 5.3 Using (R-K)-(J-K) color plot (Pozzetti & Mannucci 2000) is possible to classify 63% of the EROs sample as “old evolved galaxies” or “dusty star forming galaxies” 58 EROs have a radio counterpart down to 3σ (~ 50 μJy)

Stacking EROs Average of 740 fields centered on EROs with SNR<3, each field has an r.m.s = 17 μJy Peak = 8.4 μJy r.m.s. = 0.8 μJy SNR = 10

Stacking Empty Fields Average of 740 fields centered on random position with SNR<3 Peak = 1.4 μJy r.m.s. = 0.7 μJy SNR = 2

Stacking “Old” and “Dusty” EROs MEDIAN IMAGES OLD DUSTY

Stacking “Old” and “Dusty” EROs TypeNum.Radio Peak (microJY) RmsS/N Dusty Old MEDIAN IMAGES

Stacking “Old” and “Dusty” EROs in z bin NO DETECTION IN SINGLE REDSHIFT BIN TypeREDSHIFTNUM PEAK (MICROJY)RMSS/N DUSTY DUSTY DUSTY DUSTY DUSTY OLD OLD OLD OLD OLD

Stacking “Old” and “Dusty” PARENT SAMPLE MEDIAN IMAGES WHOLE K SELECTED SAMPLE EARLY => “TYPE” “TYPE” > 30 TypeREDSHIFTNUM PEAK (MICROJY)RMSS/N LATE LATE LATE LATE LATE EARLY EARLY EARLY EARLY EARLY

SFR in a Mass Limited Sample AIM : THE STUDY OF THE STAR FORMATION RATE AT DIFFERENT STELLAR MASS SCALE AS A FUNCTION OF REDSHIFT THE SPECIFIC SFR CALCULATED FROM EMISSION LINES VS THE STELLAR MASS OF VVDS F02 GALAXIES Vergani et al in preparationWORK IN PROGRESS !!!!!!

SFR in a Mass Limited Sample Pannella et al. 2009

SFR in a Mass Limited Sample Radio stacking in 6 mass bins and 5 redshift bins poor statistics Radio stacking in 3 mass bins and 5 redshift bins redshift bins: Mass bins : detection in the stacked images only in the last 2 bins

Very preliminary results…. WORKING IN PROGRESS!!! Statistic (number of sources) must be improved 1) New sources from 02h fields missing 2) Analysis with photometric redshift (T05 version?)