Diapositive 1

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Radio emission and properties of Spitzer
selected z2 submillimeter galaxies Alain
Omont (IAP, CNRS and Université Paris
6)
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OUTLINE Radio emission and properties of Spitzer
selected z2 submm galaxies

• Submillimeter galaxies (SMG) high-z
  Ultra-Luminous Far-IR Galaxies
• 24µm bright z2 ULIRGs PAHs/starburst vs AGN
• complete sample with very deep radio data
• Mm continuum emission. Far-IR luminosity, star
  formation rate (SFR)
• Radio emission starburst/AGN
• 1400, 610, 325 MHz, spectral index
• 1.2mm/radio, FIR/radio correlation, SFR
• Radio extension
• Other properties of Spitzer selected z2
  submillimeter galaxies
• Prospects (Herschel)
• Collaborators
• N. Fiolet, M. Polletta, F. Owen, R. Ivison, C.
  Lonsdale, S. Berta, D. Shupe, A. Beelen,

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SMGs strongest starbursts in the
Universe essential star formation in massive
galaxies at z gt 2 see Willem Baans talk

• Revealed by SCUBA/JCMT surveys at 850µm
• MAMBO/IRAM at 1.2mm ? AzTEC, LABOCA, BOLOCAM
• Easy detection of dust FIR emission at high z
• same flux at 1mm from z 0.5 to 10
• At least ULIRGs LFIR 1012-1013 Lo SFR
  100-1000 Mo/yr
• Numerous 0.1-0.3 per arcmin2
• 1000 times more numerous than locally
• Account for a significant fraction of submm
  background
• Giant starbursts at the peak of star formation,
• z 2-3 ? 1-4, in massive proto-elliptical
  galaxies
• 400 known ? 10-100 more expected from SCUBA2
  Spitzer, Herschel

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Radio emission of SMGs

• Deep radio observations are essential
• for analysis of SMGs
• (e.g. Chapman et al. 2005)
• Most SMGs are detected in deep radio
• surveys up to z2.5 (1.4GHz rms lt10µJy)
• Radio detections are crucial for
• (
• Accurate positions (SCUBA beam 14)
• ? Identification
• ? Redshift determination (100)
• AGN/starburst discrimination
• LFIRSFR estimates
• From FIR/radio correlation

Kovacs06
Chapman et al.2005
Chapman05
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• Spitzer selected z2
  24µm-bright SMGs
• Wide Spitzer surveys (SWIRE) should have
  detected a large fraction of SMGs
• To find a significant fraction of them (not so
  easy), e.g. (Lonsdale08)
• Among bright 24µm sources,
  discriminate starbursts against AGN through
  stellar bump at 5.8µm (1.6µm rest) ? strong PAH
  at 24µm (7.7µm rest)

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PAH
Starbursts
Stellar bump
AGN
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• Spitzer selected z2
  24µm-bright SMGs
• Wide Spitzer surveys (SWIRE) should have
  detected a large fraction of SMGs
• To find a significant fraction of them (not so
  easy), e.g. (Lonsdale08)
• Among bright 24µm sources, select
  starbursts against AGN through stellar bump at
  5.8µm (1.6µm rest) ? strong PAH at 24µm (7.7µm
  rest)
• Confirm by 1.2mm or 870µm pointed
  observations
• Multi-l study of a complete sample of
  5.8µm-peakers (Fiolet et al. 2009)
• in a 0.5deg2 SWIRE field
  (J10465901)
• with S24µmgt400µJy and Rgt23 ? 33
  sources
• with very deep VLA GMRT radio data
  (Owen, Ivison)
• rich other multi-l data, but lack of
  spectroscopic redshifts ? zphot

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1.2mm detection and FIR luminosity MAMBO 1.2mm
bolometer camera at IRAM-30m Moderately deep
pointed observation rms0.7mJy 14/33
3s-detections S1.2mmgt2 mJy Average ltS1.2mmgt
1.56/-0.14mJy ? 4mJy at 850µm No
individual detection in deep 160µm (and 70µm),
but after stacking ? mean ltLFIRgt
2.4 1012Lo (Tdust37K) ? most sources
are z2 ULIRGs ? SMGs
24µm 160 1200
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• Radio emission starburst/AGN
• 1400, 610, 325 MHz, spectral index
• 1.2mm/radio, FIR/radio correlation, SFR
• Radio extension

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• Radio emission of z2 Spitzer selected SMGs
• Ultra-deep VLA observation of part of the field
  (Owen Morrison 2008)
• 1.4GHz rms 5µJy ? 25/33 detections (9
  sources gt10kpc extended)
• Very deep GMRT observations of most of the field
  (Ivison et al. in prep.)
• 610MHz rms 15µJy ALL 33 sources are
  detected
• (325MHz rms 70µJy ? 17/33 detections)
• 610/1400MHz spectral indices
• About 2/3 of the sources have
  -0.4gta(610/1400)gt-1.1 compatible with
• starbursts (or obscured AGN)

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• LFIR/radio correlation
• 1.2mm/radio correlation
• Ratio 1.2mm/20cm in usual limits
• at z2 (e.g. Chapman et al. 2005)
• Except 20-35
• mm-faint/radio excess?
• ?5 to 12 AGN?
• (or faint submm radio sources SFRGs?)
• 6 of them have flat spectral index
• LFIR/Lradio correlation
• Similar behaviour

F20cm (µJy)
q
LFIR/L1.4GHz
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Fraction of strong AGN? Spatial
extension 9 sources extended on gt10kpc scale
could be AGN, but not discriminant About 25
of the sources display two AGN signposts
radio vs mm excess, flat a, extension They
could be AGN But explain the 5.8µm(1.6µm rest)
stellar peak ? no strong AGN emission
either uncertain data (SWIRE, radio ) or
AGN emission weak at 5.8µm but strong at 24µm ?
Compton thick?
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LFIR and star formation rate inferred from
radio The radio/FIR correlation allows the
derivation of LFIR for INDIVIDUAL sources
? 1012Lo lt LFIR lt 1013Lo The average value
of LFIR, 2.8x1012Lo, is somewhat
overestimated because of the AGN contribution,
but compatible with the derivation of
LFIR2.41012Lo from FIR stacked intensities The
star formation rates are thus a few 100 Mo/yr
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• Other properties of z2 Spitzer selected
  SMGs
• Large 24µm/1.2mm flux ratio
• larger than the bulk of classical SMGs because of
  larger 24µm flux
• ? strong PAH emission
• or significant AGN contribution
• Large stellar mass gt1011Mo
• derived from redshifted near-IR emission
• probably larger than the bulk of classical SMGs
  
• Similar samples may display
• Strong PAH emission (Lonsdale et al. 2008,
  Younger et al. 2009)
• Indication of extended starbursts (Huang et
  al. 2009, Dasyra et al. 2008)
• SWIRE (50deg2) includes 104 similar z2 SMGs
• They should be major mergers, significant late
  steps of assembling

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• Herschel
• Will detect 104s of SMGs in wide
• surveys with full SEDs, LFIR and SFR
• Will need multi-l data to beat confusion
• Very large surveys
• SPIRE GTO high-z HERMES 900h mapping most
  Spitzer survey fields
• (50deg2)
• GO key project ATLAS 500h, 500 deg2 ?
  shallow observations nearby and rare (lensed)
  objects

Prospects
Herschel bands and SMG SEDs
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Prospects

• Herschel (launch April 2009)
• Will detect 104s of SMGs in wide surveys with
  full SEDs, LFIR and SFR
• Will need multi-l data to beat confusion (beam
  36 at 500µm, 18 at 250µm)
• Deep radio data will be crucial
• For identifying accurate position and
  counterparts
• and thus for measuring redshifts in
  optical/near-IR
• 10µJy at 1.4GHz or 15µJy at 610MHz are
  needed
• GMRT will be essential for covering larger
  areas than VLA or complement VLA
• Priority to 20deg2 to be observed by
  Herschel/Hermes, SCUBA2 at 850µm and warm Spitzer
  at 3.6-4.5µm

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Large ratio PAH/FIR (1.2M/24µm) emission
Ratio S(1.2mm)/S(24µm) much smaller than most
SMGs whose typical SED is relatively cold,
similar to Arp 220 SED rather similar to M 82
or NGC 6090 But more luminous, without local
equivalent (Desai 07) (or composite AGN IRAS19254)
 Optimized sample 350µm detections
Unbiased sample x Literature sources


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