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A Search for Strongly-Lensed, High-z LBGs around SDSS LRGs

A Search for Strongly-Lensed, High-z LBGs around SDSS LRGs. Elizabeth Buckley-Geer Experimental Astrophysics Group Fermilab Center for Particle Astrophysics. Collaborators.

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A Search for Strongly-Lensed, High-z LBGs around SDSS LRGs

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  1. A Search for Strongly-Lensed, High-z LBGs around SDSS LRGs Elizabeth Buckley-Geer Experimental Astrophysics Group Fermilab Center for Particle Astrophysics 23rd IAP Colloquium

  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, … 23rd IAP Colloquium

  3. Outline • Motivation • SDSS Arc Search • Follow-up Observations • Sample Properties • Lens Modeling • Plans 23rd IAP Colloquium

  4. Motivation • 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 23rd IAP Colloquium

  5. 8 o’clock arc APO 3.5m g-band image and Keck LRIS spectrum zlens = 0.38 23rd IAP Colloquium

  6. SDSS 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 23rd IAP Colloquium

  7. Follow-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 23rd IAP Colloquium

  8. 15 Candidate Systems 23rd IAP Colloquium

  9. 2 Systems Rejected by Follow-Up 23rd IAP Colloquium

  10. 6 Spectroscopically Confirmed Lensing Systems This system also found by V. Belokurov et al. dubbed the “Cosmic Horseshoe” astro-ph/0706.2326 We obtained spectra in Feb/March 2007 compared with May for the published observation 23rd IAP Colloquium

  11. 7 Remaining Systems Still Need Follow-Up Confirmation 23rd IAP Colloquium

  12. Comparison of SDSS Discovery and APO 3.5m Follow-Up Images 23rd IAP Colloquium

  13. lrg_2_2811 (“Clone”) Subaru FOCAS V-band image and spectrum (M. Oguri) zlens = 0.42 23rd IAP Colloquium

  14. lrg_4_606 APO 3.5m SPIcam gri image and DIS spectrum (unfluxed) zlens = 0.49 23rd IAP Colloquium

  15. lrg_3_757 SDSS 2.5m gri image and APO 3.5m DIS spectrum (unfluxed) zlens = 0.44 23rd IAP Colloquium

  16. lrg_3_817 APO 3.5m SPIcam gri image and DIS spectrum (unfluxed) zlens= 0.35 23rd IAP Colloquium

  17. Sample 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 23rd IAP Colloquium

  18. M/L vs. Radius Comparison Weak lensing by CNOC2 groups (Parker et al. 2005) Elliptical galaxies: dynamics and X-rays (Bahcall et al. 1995) SDSS Arc Search Sample Keeton et al. (1998) lenses SLACS lenses (Treu et al. 2006, Koopmans et al. 2006) 23rd IAP Colloquium

  19. Lens Modeling • Use lensmodel/gravlens (C. Keeton, astro-ph/0102340) • Image positions from SExtractor • Assume a SIE mass profile • Flat cosmology, Wm=0.3, WL=0.7, H0=100 h km s-1 Mpc-1 • Fit for the Einstein radius θEIN • Determine velocity dispersion and mass contained within θEIN • Have 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 images for the clone. Get consistent results from the two images of the clone. Show results from fit to Subaru data. • Also have started to use LENSVIEW (R. Wayth & R.L. Webster, MNRAS 372 (2006) 1187-1207). Have a preliminary fit for “The Clone” that qualitatively agrees with the lensmodel results. 23rd IAP Colloquium

  20. Modeling Results “8 o’clock arc” θEIN = 3.35”,ε = 0.53, PA = 12.8 deg χ2/dof = 1.04 σ = 392 km s-1 REIN = 12.2 h-1 kpc MEIN = 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 deg χ2/dof = 0.5 σ = 440 km s-1 REIN = 14.9 h-1 kpc MEIN = 2.1 x 1012 h-1 M Total Magnification = 27 23rd IAP Colloquium

  21. LENSVIEW Results for “The Clone” Tangential Critical curve Input Image Model Image Tangential caustic Source 23rd IAP Colloquium

  22. Plans • 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 23rd IAP Colloquium

  23. Masses and Einstein Radii D. Kubik (2007) 23rd IAP Colloquium

  24. M/L vs. Radius D. Kubik (2007) 23rd IAP Colloquium

  25. M/L vs. Mass D. Kubik (2007) 23rd IAP Colloquium

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