A Search for Bright, StronglyLensed, Highz Galaxies in the SDSS

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Strong Lensing Studies at Fermilab
Elizabeth Buckley-Geer for the Experimental
Astrophysics Group Fermilab Center for Particle
Astrophysics
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Collaborators

• Fermilab H. Lin, D. Kubik, H.T. Diehl, S.
  Allam, D. Tucker, E. Buckley-Geer, J. Kubo, J.
  Annis, J. Frieman, D. Finley, J. Estrada, D.
  McGinnis, V. Scarpine, Fermilab Cosmology
  Analysis Group
• D. Schneider, M. Oguri, A. Shapley, A. Baker, D.
  Lutz, J.A. Smith, J. Brinchmann, M. Strauss,
  M.-S. Shin, C. Kochanek, C. Tremonti,

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Outline

• SDSS Arc Search
• Follow-up Observations
• Sample Properties
• Lens Modeling for LRG-4-606
• A lens from the BCS data

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SDSS Arc Search

• The candidates come from two different samples.
• Potential red galaxy lenses from SDSS DR5 (8000
  deg2)
• 221,000 luminous red galaxies (LRGs)
• 29,000 brightest cluster galaxies (BCGs) from
  maxBCG cluster sample (J. Annis)
• SDSS DR5 CAS database query (D. Kubik)
• Blue galaxies (g-r and r-i color cuts)
• 57,000 systems returned with n1 or more blue
  objects
• Rank systems by number of blue objects n
• Visual inspections
• Inspect all systems (1081) with n 3 blue
  objects
• 4 separate inspectors looked at SDSS CAS gri
  color jpeg images
• Follow up 14 candidate systems flagged by 2 or
  more inspectors
• Plus 1 more (clone) from single-inspector eye
  scan of n2 LRG list
• Interacting-merging galaxy sample (S.Allam)
• Start with 15,000 isolated galaxies and 38,000
  isolated galaxy pairs from SDSS DR5
• Exclude spiral galaxies to avoid false detections
  of lenses
• Apply additional selection cuts.
• Yields 17500 objects which after visual
  examination reduces to 3000 objects.

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Follow-up Observations

• The search identified N candidate systems
• Follow-up observing program (Fermilab group) on
  Apache Point Observatory (APO) 3.5m telescope
• Arcs are bright (r 20-22) and high SB (?r
  23-24 mag/arcsec2)
• SPIcam gri imaging (15 min exposures per filter)
  for deeper images (SDSS discovery images are only
  54 seconds on a 2.5m telescope)
• DIS spectroscopy (45 min exposures) of brighter
  targets for source and lens redshifts
• We curently have 9 spectroscopically confirmed
  lensing systems.
• 6 with z 2
• 3 have z 1.0
• Lenses typically have z 0.4
• We also have HST and Spitzer data for one system
  (lrg_2_2811)

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9 Spectroscopically Confirmed Lensing Systems
SSA_1113 zl 0.35 zs 0.77
lrg-4-606 zl0.49 zs 2.03
lrg-3-817 zl 0.35 zs 2.26
8 oclock arc zl 0.38 zs 2.73
lrg-3-227 zl 0.45 zs 0.98
lrg-2-2811 zl 0.42 zs 2.0 The Clone
lrg-4-581 zl 0.43 zs 0.97 Cosmic Snowman
lrg-3-757 zl 0.44 zs 2.38 Cosmic Horseshoe
SSA_1343 zl 0.34 zs 2.1
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Example Spectra
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Comparison of SDSS, Subaru and HST Data for
lrg-2-2811
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Spitzer Data for lrg-2-2811
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Lens Modeling Results for lrg-2-2811- The Clone

• Using LENSVIEW (R. Wayth R.L. Webster, MNRAS
  372 (2006) 1187-1207).
• Assume a SIE mass profile
• Flat cosmology, Wm0.3, WL0.7, H0100 h km s-1
  Mpc-1
• Fit for the Einstein radius ?EIN

Model Image
Source
Residuals
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Modeling for lrg-4-606

• Use GALFIT to model the light profiles of the
  galaxies and the arcs

Input
Model
i band
Combination of Sersic profiles for the galaxies
and exponential disks for the arcs 18 objects
sky ?2/dof 1.4
Residuals
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GALFIT r-band
Residuals
Input
Model
Use i-band parameters for galaxies and allow
magnitude and position to vary. Allow all arc
parameters to vary. Add small red galaxy that is
visible at the top left of the arc (it shows
up most clearly in r).
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GALFIT g-band
Residuals
Input
Model
Use i-band parameters for galaxies and allow
magnitude and position to vary. Allow all arc
parameters to vary.
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Color-magnitude plot
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LENSVIEW Input
Use g-band image Add small red galaxy at correct
location using g-band magnitude estimated from
color-magnitude plot
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First try using Lensview
Input
Model
SIE ?EIN 7.4 Axis ratio 0.77 PA 44.7
Source
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BCS data Elliot Arc
Parameters (using Lensmodel) ?EIN
7.5" Ellipticity 0.269 PA -32.8 deg ?2/dof
1.03 s 826 km s-1 REIN 28.2 h-1 kpc MEIN
1.4x1013 h-1 M
A4
A1
A3
A2
This system is included in a recent proposal that
we submitted to get HST imaging data.
The galaxy cluster surrounding the arc has an
Ngals 71 and a mass of M200 4x1014 h-1 M
which makes it a very rich cluster. GMOS spectra
taken with Gemini South in August 2007 give zl
0.38 and zs 0.9