Gravitational lensing and the problem of faint galaxies

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Gravitational lensing and the problem of faint
galaxies

• Alicia Berciano Alba (JIVE / Kapteyn institute)
• Mike Garret (JIVE)
• Leon Koopmans (Kapteyn institute)

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The problem of sub-mm Galaxies
Hughes et al. (Nature 1998)
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Nature of sub-mm galaxies

• SCUBA sources faint dusty star forming galaxies
  at high z

obscured in optical but not in sub-mm and radio
At low z ? rare objects (M82, Arp220)
At high z ? the peak is shifted from FIR to sub-mm
electrons
die like SN
Massive stars
a lot of dust
A lot of uv-radiation
FIR Emission
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Solution Gravitational lensing as a telescope

• If we are lucky

very massive object Between sub-mm source
and us
several images with magnification in size and
flux density
we can see the iceberg below the sea
strong GL effect
YES, we are
Abell 2218
GL in clusters of galaxies
MS0451.6-0305
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Abell 2218
Sources Star forming galaxy (z2.516) ? 3
images arc289 (Z1.034)
arc289
Kneib et al. (2004)
Data Optical images (HST) NIR imagin /
spectroscopy (WHT/ Keck) Sub-mm (SCUBA 850
mm) Radio (VLA 8.2 GHz / WSRT 1.4 GHz)
Kneib et al. (2004) Knudsen (2004) Sheth et al.
(2004)
Garrett et al. (2005)
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MS0451.6-0305
Borys et al. (2004)

• DATA
• - Optical image (HST)
• - VLT (Very Large Telescope) spectrocopy
• - Sub-mm (SCUBA 850 mm) ? solid line
• - X-ray (Chandra) ? dotted line
• - X-ray point sources (Molar et al. 2002) ?
  croses
• - NIR (Near Infra-Red) objects ?
  circles

SOURCES - 2 lens images of a fold arc (ARC1)
? LBG - 3 lens images of 2 objects (B/C) ? 2
EROs - P ? very blue object
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Trying to find the radio counterpart
Clusters centre

• Data
• From VLA archive
• Freq 1.36 GHz (L-band) AB config.
• Obs time (on-source ) 7h 46min
• 1s rms 9 mJy / beam

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The Comparison Between Sub-mm and radio
alineation problem

• Radio emission is coincident with the sub-mm
  emission extended on the same angular scale.
• Radio sub-mm emission due to the same
  source(s)
• Two emissions magnified by GL effect
• Radio ? St gt 100 mJy (few tens mJy)
• Sub-mm ? St gtgt10 mJy (few mJy)

S850 mm / S1.4 Ghz 100 ? as we expect
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Borys et al. conclusions
ARC1 (LBG)

• Sources of sub-mm emission

B/C pair (EROs)
2/3 of the total flux
Borys et al. cant reproduce the sub-mm
emission!!!
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Ourpreliminar Results

• B1/C1 at the edge of the radio emission ? maybe
  not related with the emissions?
• We can explain the elongation in the top of
  sub-mm emission ? new radio source
• We can explain the gap in the borys simulation ?
  3 new radio sources
• No radio detection in B3/C3 ? is not a surprise

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Future Work

• Obtain the HST and SCUBA images from Borys to
  make a correct alignament with the radio image
• know the error positions of ARC1 and EROs
• Try to reproduce the detailed morphology of the
  radio map with a similar simulation used by Borys
• Understand whats going on with the radio image
  in terms of lensing model
• Make a tapered low resolution and higher
  resolution uniformly weighted image of the radio
  data
• Look for more data in the VLA rachive (5 and 8
  GHz)
• Apply for VLA data in A configuration ? 1
  resolution (instead of the actual 5 resolution)

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Conclusions

• We detect the second multiply imaged radio
  emission associated with massive cluster lensing
• We find 1 radio source to explain the the excess
  of scuba emission in the top left part of the
  image
• We find 3 radio sources to explain the gap in
  Borys simulation
• We cant be sure about the contribution of the
  B/C pair in the radio and sub-mm emissions

The answer (I hope) in the next meeting
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(No Transcript)
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Our preliminar results

• B1/C1 are not in the peak of the radio image
• The peak of the radio image have the same
  orientation as the sub-mm image
• We can explain the gap in the Borys simulation ?
  2 radio images
• The middle radio source could be associated with
  one of the Tanakas EROs

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Summary

• The only way to detect this sources is through
  the GL effect
• We have 2 systems with sub-mm and radio to study
  their nature ? we are looking for more
• We must finish the analysis of radio data in
  MS0451.6-0305
• The case of MS0451.6-0305 is more complex than
  A2218 ? we need better radio images to know the
  nature of the sub-mm emmision

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The problem of sub-mm Galaxies

• Faint SMG dominate energetically the cosmic
  far-infrared background (Knudsen 2004)
• SCUBA-detected galaxies are often extremely faint
  in the optical because the dust responsible for
  the sub-mm luminosity absorbs radiation at other
  wavelenghts ? redshifts, morphologies and
  spectral energy distributions are dificult to
  obtain
• With current sensitivity limits, actual
  telescopes can only detect the bright tail of the
  SMG population
• Flux density of SMG ? lt 2mJy

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Garrett et al. 2005
Abell 2218 (radio)

• VLA 8.2 GHz
• Contours -3, 3, 4, 7, 10
• 1-s noise level 6 m-Jy / beam
• Integration time 24 h

WSRT 1.4 GHz Contours -3, 3, 5, 10, 20, 40 1-s
noise level 15 mJy / beam Integration time12 h
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Abell 2218
Sources Star forming galaxy (z2.516) ? 3
images arc289 (Z1.034)
Data Optical images (HST) NIR imagin /
spectroscopy (WHT/ Keck) Sub-mm (SCUBA 850
mm) Radio (VLA 8.2 GHz / WSRT 1.4 GHz)
Kneib et al. (2004) Knudsen et al. (2004) Sheth
et al. (2004)
Garrett et al. (2005)
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Abell 2218 (sub-mm)
Kneib et al. (2004b)

• Sub-mm sources (SCUBA 850 mJy)
• Star forming galaxy (z2.516) ? 3 images
• SMM J1635966118 (Z1.034) ? arc289

SMM A
SMM B
SMM C
Arc289
Knudsen (2004)
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Abell 2218
Sources Star forming galaxy (z2.516) ? 3
images arc289 (Z1.034)
arc289
Kneib et al. (2004)
Data Optical images (HST) NIR imagin /
spectroscopy (WHT/ Keck) Sub-mm (SCUBA 850
mm) Radio (VLA 8.2 GHz / WSRT 1.4 GHz)
Kneib et al. (2004) Knudsen (2004) Sheth et al.
(2004)
Garrett et al. (2005)
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Nature of the sources
problem
No x-ray detection of C2

• ARC1
• VLT spectroscopy ? LBG (Lyman Break Galaxy) at
  z2.911
• Lens model (kneib et al. 1993 / 96) ?
  identification of ARC1 ci
• B/C pair
• NIR colormagnitude diagram ? 2 EROs
• Lens model ?identification of the 3
  images with correct parity if B/C pair its at
  z2.85

ARC1 and B/C at aprox. same z ? separation in
source plane 10 kpc ? 3 interacting galaxies ?
origin of a violent starburst revealed by the
strong sub-mm emission
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Which is the source of the sum-mm emmision??

• Connection between sub-mm galaxies and EROs well
  stablished
• ARC1 spectrum similar to the most absorved LBG ?
  reddest and most dust-extinted

Simulation - blank SCUBA-like map with
sources in B1,B2,B3, ARC1 - relative fluxes
fixed by lensing model predictions -
the peak flux needs to match the
observations ? 12 mJy
They CANT reproduce the sub-mm
observation only with this 2 sources
dusty starbust 4 to the NE of B3/C3 (Tanaka et
al. 2003)

• - We need the two sources to expain the sub-mm
  observations
• 2/3 of sub-mm flux is coming from the EROs

Conclusions
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More problems