april 2007 des collaboration meeting 1 strong lensing studies at fermilab elizabeth buckley-geer for...
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April 2007 DES Collaboration Meeting 1
Strong Lensing Studies at Fermilab
Elizabeth Buckley-Geer for theExperimental Astrophysics Group
Fermilab Center for Particle Astrophysics
April 2007 DES Collaboration Meeting 2
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)– < 10” from LRG or BCG– 57,000 systems returned with n=1 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 n=2 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
lrg-4-606zl=0.49zs = 2.03
lrg-3-817zl = 0.35 zs = 2.26
lrg-3-227zl = 0.45zs = 0.98
lrg-4-581zl = 0.43zs = 0.97“CosmicSnowman”
SSA_1113zl = 0.35zs = 0.77
lrg-2-2811zl = 0.42zs = 2.0“The Clone”
lrg-3-757zl = 0.44zs = 2.38“CosmicHorseshoe”
8 o’clock arczl = 0.38zs = 2.73
SSA_1343zl = 0.34zs = 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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Tangential caustic
TangentialCritical curve
Lens Modeling Results for lrg-2-2811- ‘The Clone’
Model Image Source
•Using LENSVIEW (R. Wayth & R.L. Webster, MNRAS 372 (2006) 1187-1207).•Assume a SIE mass profile•Flat cosmology, m=0.3, =0.7, H0=100 h km s-1 Mpc-1 •Fit for the Einstein radius θEIN
Residuals
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Input Model
ResidualsCombination of Sersic profiles for thegalaxies and exponential disks for the arcs18 objects + skyχ2/dof = 1.4
Use GALFIT to model the light profiles of the galaxies and the arcs
Modeling for lrg-4-606
i band
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GALFIT r-bandResiduals
Model
Input
Use i-band parameters for galaxiesand allow magnitude and position to vary. Allow all arc parameters tovary.Add small red galaxy that is visibleat the top left of the arc (it shows upmost clearly in r).
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GALFIT g-bandResiduals
Model
Input
Use i-band parameters for galaxiesand allow magnitude and position to vary. Allow all arc parameters tovary.
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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
SIEθEIN = 7.4”Axis ratio = 0.77PA = 44.7°
Input Model
Source
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BCS data – Elliot ArcParameters (using Lensmodel)θEIN = 7.5"Ellipticity = 0.269PA = -32.8 degχ2/dof = 1.03σ = 826 km s-1
REIN = 28.2 h-1 kpcMEIN = 1.4x1013 h-1 M
The galaxy cluster surrounding the arc hasan 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
A4
A3
A1
A2
This system is included in arecent proposal that we submittedto get HST imaging data.