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July 5 2007July 5 2007 23rd IAP Colloquium23rd IAP Colloquium 11
A Search for Strongly-Lensed, High-z LBGs around SDSS LRGs
Elizabeth Buckley-GeerExperimental Astrophysics Group
Fermilab Center for Particle Astrophysics
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CollaboratorsCollaborators
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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OutlineOutline
MotivationMotivation SDSS Arc SearchSDSS Arc Search Follow-up ObservationsFollow-up Observations Sample PropertiesSample Properties Lens ModelingLens Modeling PlansPlans
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MotivationMotivation cB58 (Yee et al. 1996)
– Discovered serendipitously in CNOC1 cluster redshift survey– z = 2.72 Lyman break galaxy (LBG) lensed by z = 0.37
brightest cluster galaxy (BCG)– Bright, blue object (r = 20.4), 6” away from BCG– Bright enough to be easily seen in SDSS and to have an
SDSS spectroscopic redshift!
8 o’clock arc (Allam et al. 2007)– Discovered serendipitously in inspection of SDSS DR4
interacting galaxy pairs sample– z = 2.73 LBG lensed by z = 0.38 SDSS luminous red galaxy
(LRG)– Bright, blue arc (total r = 19), ~4” away from LRG– Easy absorption line redshift in 20 min DIS spectrum on APO
3.5m
Start systematic search for more systems like cB58 and the 8 o’clock arc in the SDSS
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8 o’clock arc
APO 3.5m g-band image and Keck LRIS spectrum
zlens = 0.38
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SDSS Arc SearchSDSS Arc Search
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– Look for arc-like morphology– Reject HII regions, spiral arms, merging galaxies, etc.– 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
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Follow-up ObservationsFollow-up Observations
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
Additional Hobby-Eberly Telescope (HET) spectroscopic follow-up program (PI D. Schneider) of fainter targets
Subaru FOCAS imaging and spectroscopy (M. Oguri) of “Clone” system
APO and HET programs are ongoing
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15 Candidate Systems
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2 Systems Rejected by Follow-Up
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6 Spectroscopically Confirmed Lensing Systems
This system also found byV. Belokurov et al. dubbedthe “Cosmic Horseshoe”astro-ph/0706.2326We obtained spectra in Feb/March 2007 compared with May for the published observation
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7 Remaining Systems StillNeed Follow-Up Confirmation
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Comparison of SDSS Discovery and APO 3.5m Follow-Up Images
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lrg_2_2811 (“Clone”)
Subaru FOCAS V-band image and spectrum (M. Oguri)
zlens = 0.42
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lrg_4_606
APO 3.5m SPIcam gri image and DIS spectrum (unfluxed)
zlens = 0.49
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SDSS 2.5m gri image and APO 3.5m DIS spectrum (unfluxed)
lrg_3_757
zlens = 0.44
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lrg_3_817
APO 3.5m SPIcam gri image and DIS spectrum (unfluxed)
zlens= 0.35
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Sample PropertiesSample Properties Current follow-up results for 15 candidate systems
– 6 spectroscopically confirmed 4 with z = 2.0-2.4: “BX” galaxies (z~2 Lyman break galaxies) 2 have z = 1.0 and z = 0.4
– 2 rejected, remaining 7 still need follow-up confirmation
Lensed images are bright (r ~ 20-22) and high SB (r ~ 23-24 mag/arcsec2) Lens galaxies in z ~ 0.2-0.5 range, but most have z ~ 0.4
Einstein radius, mass, and M/L analysis (D. Kubik master’s thesis)– Estimate Einstein radius by circle fit to lensed images– Einstein radii 3-10”, or 10-40 h-1 kpc– Masses within Einstein radii of 1012 - 1013 h-1 M
– “Intermediate” regime: lensing by groups and centers of clusters– M/L (g-band rest frame) of 10-140 h (M/L) on scales of 10-40 h-1 kpc
Consistent with trends from dynamical and X-ray M/L measurements for ellipticals on similar scales
Complementary to other strong lensing results on smaller scales, and weak lensing results on larger scales
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M/L vs. Radius Comparison
SDSS Arc Search Sample
Weak lensing by CNOC2 groups (Parker et al. 2005)
Keeton et al. (1998) lenses
SLACS lenses (Treu et al. 2006, Koopmans et al. 2006)
Elliptical galaxies: dynamics and X-rays (Bahcall et al. 1995)
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Lens ModelingLens Modeling Use Use lensmodel/gravlenslensmodel/gravlens (C. Keeton, astro-ph/0102340) (C. Keeton, astro-ph/0102340) Image positions from SExtractorImage positions from SExtractor Assume a SIE mass profileAssume a SIE mass profile Flat cosmology, Flat cosmology, mm=0.3, =0.3, =0.7, H=0.7, H00=100 h km s=100 h km s-1-1 Mpc Mpc-1-1
Fit for the Einstein radius Fit for the Einstein radius θθEINEIN
Determine velocity dispersion and mass contained within Determine velocity dispersion and mass contained within θθEINEIN
Have modeled the “8 o’clock arc” and the “Clone” so farHave modeled the “8 o’clock arc” and the “Clone” so far Used the SPIcam image for the 8 o’clock arc and both the SDSS and Subaru Used the SPIcam image for the 8 o’clock arc and both the SDSS and Subaru
images for the clone. Get consistent results from the two images of the clone. images for the clone. Get consistent results from the two images of the clone. Show results from fit to Subaru data.Show results from fit to Subaru data.
Also have started to use Also have started to use LENSVIEWLENSVIEW (R. Wayth & R.L. Webster, MNRAS 372 (R. Wayth & R.L. Webster, MNRAS 372 (2006) 1187-1207). Have a preliminary fit for “The Clone” that qualitatively (2006) 1187-1207). Have a preliminary fit for “The Clone” that qualitatively agrees with the agrees with the lensmodellensmodel results. results.
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Modeling ResultsModeling Results“8 o’clock arc”θEIN = 3.35”,ε = 0.53, PA = 12.8 degχ2/dof = 1.04σ = 392 km s-1
REIN = 12.2 h-1 kpcMEIN = 1.4 x 1012 h-1 M M/L (rest frame g-band) = 13.8 h M /L
Total Magnification = 12.8
“Clone”θEIN = 3.83”,ε = 0.291, PA = -73.6 degχ2/dof = 0.5σ = 440 km s-1
REIN = 14.9 h-1 kpcMEIN = 2.1 x 1012 h-1 M Total Magnification = 27
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LENSVIEW Results for LENSVIEW Results for “The Clone”“The Clone”
Model ImageInput Image
Source
TangentialCritical curve
Tangential caustic
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PlansPlans Observations
– Complete follow-up confirmation programs at APO and HET– HST Cycle 16 and Spitzer Cycle 4: 8 o’clock arc and clone – Gemini NIRI spectroscopy of 3 confirmed z > 2 systems (2007B)– IRAM mm CO and continuum observations of z > 2 systems– Will propose for IRTF near-IR imaging follow-up
Analyses– More detailed lens models
Constrain lens mass profiles in group/cluster core environments– Simulations to determine selection effects– Understand source and lens redshift distributions
More SDSS arc searches – Inspect existing n ≤2 query search systems– Search around fainter, higher-z red galaxies, including Stripe 82 coadds– Increase search radius to get cluster-scale lensing systems– Implement automated search methods
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D. Kubik (2007)
Masses and Einstein Radii
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D. Kubik (2007)
M/L vs. Radius
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D. Kubik (2007)
M/L vs. Mass
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