Strong Lensing Studies at Fermilab Elizabeth BuckleyGeer for

Strong Lensing Studies at Fermilab Elizabeth Buckley-Geer for the Experimental Astrophysics Group Fermilab Center for Particle Astrophysics April 2007 DES Collaboration Meeting 1

Collaborators u 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. Mc. Ginnis, V. Scarpine, … Fermilab Cosmology Analysis Group u D. Schneider, M. Oguri, A. Shapley, A. Baker, D. Lutz, J. A. Smith, J. Brinchmann, M. Strauss, M. -S. Shin, C. Kochanek, C. Tremonti, … April 2007 DES Collaboration Meeting 2

Outline u u u SDSS Arc Search Follow-up Observations Sample Properties Lens Modeling for LRG-4 -606 A lens from the BCS data April 2007 DES Collaboration Meeting 3

SDSS Arc Search u The candidates come from two different samples. ► Potential red galaxy lenses from SDSS DR 5 (8000 deg 2) u u 221, 000 luminous red galaxies (LRGs) 29, 000 brightest cluster galaxies (BCGs) from max. BCG cluster sample (J. Annis) SDSS DR 5 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) u u April 2007 Start with 15, 000 isolated galaxies and 38, 000 isolated galaxy pairs from SDSS DR 5 Exclude spiral galaxies to avoid false detections of lenses Apply additional selection cuts. Yields 17500 objects which after visual examination reduces to 3000 objects. DES Collaboration Meeting 4

Follow-up Observations u u The search identified N candidate systems Follow-up observing program (Fermilab group) on Apache Point Observatory (APO) 3. 5 m telescope ► Arcs are bright (r ~ 20 -22) and high SB ( r ~ 23 -24 mag/arcsec 2) ► SPIcam gri imaging (15 min exposures per filter) for deeper images (SDSS discovery images are only 54 seconds on a 2. 5 m telescope) ► DIS spectroscopy (45 min exposures) of brighter targets for source and lens redshifts u We curently have 9 spectroscopically confirmed lensing systems. ► 6 with z ≥ 2 ► 3 have z ~1. 0 ► Lenses typically have z ~ 0. 4 u We also have HST and Spitzer data for one system (lrg_2_2811) April 2007 DES Collaboration Meeting 5

9 Spectroscopically Confirmed Lensing Systems April 2007 lrg-3 -817 zl = 0. 35 zs = 2. 26 SSA_1113 zl = 0. 35 zs = 0. 77 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” DES Collaboration Meeting lrg-4 -606 zl=0. 49 zs = 2. 03 8 o’clock arc zl = 0. 38 zs = 2. 73 SSA_1343 zl = 0. 34 zs = 2. 1 6

Example Spectra April 2007 DES Collaboration Meeting 7

Comparison of SDSS, Subaru and HST Data for lrg-2 -2811 April 2007 DES Collaboration Meeting 8

Spitzer Data for lrg-2 -2811 April 2007 DES Collaboration Meeting 9

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, Wm=0. 3, WL=0. 7, H 0=100 h km s-1 Mpc-1 • Fit for the Einstein radius θEIN Model Image Source Residuals Tangential caustic Tangential Critical curve April 2007 DES Collaboration Meeting 10

Modeling for lrg-4 -606 u Use GALFIT to model the light profiles of the galaxies and the arcs Input Residuals April 2007 Model i band Combination of Sersic profiles for the galaxies and exponential disks for the arcs 18 objects + sky χ2/dof = 1. 4 DES Collaboration Meeting 11

GALFIT r-band Residuals Model April 2007 Input 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). DES Collaboration Meeting 12

GALFIT g-band Residuals Model April 2007 Input Use i-band parameters for galaxies and allow magnitude and position to vary. Allow all arc parameters to vary. DES Collaboration Meeting 13

Color-magnitude plot April 2007 DES Collaboration Meeting 14

LENSVIEW Input Use g-band image Add small red galaxy at correct location using g-band magnitude estimated from color-magnitude plot April 2007 DES Collaboration Meeting 15

First try using Lensview Input Model SIE θEIN = 7. 4” Axis ratio = 0. 77 PA = 44. 7° Source April 2007 DES Collaboration Meeting 16

BCS data – Elliot Arc Parameters (using Lensmodel) θEIN = 7. 5" Ellipticity = 0. 269 PA = -32. 8 deg χ2/dof = 1. 03 σ = 826 km s-1 REIN = 28. 2 h-1 kpc MEIN = 1. 4 x 1013 h-1 M A 4 A 1 A 2 A 3 The galaxy cluster surrounding the arc has an Ngals ≥ 71 and a mass of M 200 ~ 4 x 1014 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 April 2007 This system is included in a recent proposal that we submitted to get HST imaging data. DES Collaboration Meeting 17