July 5 2007 23rd IAP Colloquium 1 A Search for Strongly-Lensed, High-z LBGs around SDSS LRGs...

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


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, …


OutlineOutline

MotivationMotivation SDSS Arc SearchSDSS Arc Search Follow-up ObservationsFollow-up Observations Sample PropertiesSample Properties Lens ModelingLens Modeling PlansPlans


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


8 o’clock arc

APO 3.5m g-band image and Keck LRIS spectrum

zlens = 0.38


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


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


15 Candidate Systems


2 Systems Rejected by Follow-Up


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


7 Remaining Systems StillNeed Follow-Up Confirmation


Comparison of SDSS Discovery and APO 3.5m Follow-Up Images


lrg_2_2811 (“Clone”)

Subaru FOCAS V-band image and spectrum (M. Oguri)

zlens = 0.42


lrg_4_606

APO 3.5m SPIcam gri image and DIS spectrum (unfluxed)

zlens = 0.49


SDSS 2.5m gri image and APO 3.5m DIS spectrum (unfluxed)

lrg_3_757

zlens = 0.44


lrg_3_817

APO 3.5m SPIcam gri image and DIS spectrum (unfluxed)

zlens= 0.35


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


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)


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.


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


LENSVIEW Results for LENSVIEW Results for “The Clone”“The Clone”

Model ImageInput Image

Source

TangentialCritical curve

Tangential caustic


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


D. Kubik (2007)

Masses and Einstein Radii


D. Kubik (2007)

M/L vs. Radius


D. Kubik (2007)

M/L vs. Mass

July 5 2007 23rd IAP Colloquium 1 A Search for Strongly-Lensed, High-z LBGs around SDSS LRGs...

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