radio observations in vvds field : past - present - future p.ciliegi(oabo), marco bondi (ira) g....
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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?)