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

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

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 + 313 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 (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

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<0.7Black 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<0.5Black 0.5<z<1.1

Type 3+4(late)

LUMINOSITY FUNCTIONS

LF=0 (1+z)k

(L/L*)

where

L=L0 (1+z)

= -1.84= 2.63K= 0.43

SFR(radio)=SFR(optical) line

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

SFR(radio) vs SFR(optical)

Log (sfrVVDS)-Log (SFRradio)=

<0.73> +/- 0.02

Expected 0.74From FUV (1500Å) (Hopkins et al 2001)

SFR density (1+z)2.15

Uncorrected SFR form FUV (Tresse et al. 2007)

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)<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)

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

Type Num. Radio Peak

(microJY)

Rms S/N

Dusty 200 9.6 1.5 6.4

Old 330 6.6 1.2

5.5

MEDIAN IMAGES

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

Type REDSHIFT NUM

PEAK

(MICROJY) RMS S/N

DUSTY 1.00 - 1.25 54 15.6 2.9 5.4

DUSTY 1.25 - 1.50 30 10.8 3.9 2.7

DUSTY 1.50 - 2.00 53 12.9 2.9 4.4

DUSTY 2.00 - 3.00 34 10.1 3.8 2.7

DUSTY 3.00 - 4.00 12 12.3 6.2 2.0

OLD 1.00 - 1.25 123 6.8 1.9 3.6

OLD 1.25 - 1.50 100 6.7 2.3 2.9

OLD 1.50 - 2.00 62 8.3 2.7 3.1

OLD 2.0 0 - 3.00 12 23.5 6.6 3.6

OLD 3.00 - 4.00 6 18.9 8.5 2.2

Stacking “Old” and “Dusty” PARENT SAMPLE MEDIAN IMAGES WHOLE K SELECTED SAMPLE

EARLY => “TYPE” < 13 LATE=> “TYPE” > 30

Type REDSHIFT NUM

PEAK

(MICROJY) RMS S/N

LATE 1.00 - 1.25 3930 3.91 0.4 9.8

LATE 1.25 - 1.50 789 5.52 0.8 6.9

LATE 1.50 - 2.00 1140 4.28 0.7 6.1

LATE 2.00 - 3.00 1211 2.83 0.6 4.7

LATE 3.00 - 4.00 340 3.53 1.2 2.9

EARLY 1.00 - 1.25 1425 3.17 0.6 5.3

EARLY 1.25 - 1.50 170 4.47 1.7 2.6

EARLY 1.50 - 2.00 230 5.01 1.5 3.3

EARLY 2.0 0 - 3.00 120 4.17 2.1 2.0

EARLY 3.00 - 4.00 145 7.03 3.3 2.1

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 preparation WORK 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: 0.15 - 0.35 0.35 - 0.50 0.5 - 0.7 0.7 - 0.9 0.9 - 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

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?)