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The contribution of radio observations for multi- λ surveys

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.

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The contribution of radio observations for multi- λ surveys

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

  2. 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'

  3. 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

  4. 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

  5. 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.

  6. Results: Radio Source Counts Bondi et al. 2003 • 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 andstarburst contribution to the sub-mJy population

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

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

  9. VVDS GMRT RADIO SURVEY Bondi et al 2007 • 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 + 313 limits • 75% of the sample optically identified (colors, morphological type & z phot)

  10. VVDS GMRT 0.6 GHz • Evidences of different populations at the sub-mJy level. • Median spectal index (0.15 - 0.5 mJy) flatter than that brighter sources. Contribution from AGN and radio quiet QSO. • The contribution of starburst become important below 0.2 mJy 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)

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

  12. LUMINOSITY FUNCTIONS Type 3+4 (late) Red 0<z<0.5 Black 0.5<z<1.1 LF=0 (1+z)k (L/L*) where L=L0 (1+z)  = -1.84 = 2.63 K= 0.43

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

  14. Log (sfrVVDS)- Log (SFRradio)= <0.73> +/- 0.02 Expected 0.74 From FUV (1500Å) (Hopkins et al 2001) SFR density (1+z)2.15 Uncorrected SFR form FUV (Tresse et al. 2007)

  15. 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

  16. The radio properties of EROs • Starting from the K-band selected photometric sample, obtained 898 objects with K(Vega)<20.25 and (R-K)>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)

  17. 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

  18. 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

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

  20. Stacking “Old” and “Dusty” EROs MEDIAN IMAGES

  21. Stacking “Old” and “Dusty” EROs in z bin NO DETECTION IN SINGLE REDSHIFT BIN

  22. Stacking “Old” and “Dusty” PARENT SAMPLE MEDIAN IMAGES WHOLE K SELECTED SAMPLE EARLY => “TYPE” < 13 LATE=> “TYPE” > 30

  23. SFR in a Mass Limited Sample Vergani et al in preparation WORK IN PROGRESS !!!!!! 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

  24. SFR in a Mass Limited Sample Pannella et al. 2009

  25. 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: 0.15 - 0.350.35 - 0.500.5 - 0.70.7 - 0.90.9 - 1.2 Mass bins : 8.1 - 9.7 9.7 - 10.5 10.5 - 12.0 detection in the stacked images only in the last 2 bins

  26. 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?)

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