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DIRECT DETECTION OF STRONG GALAXY-GALAXY LENSING IN SDSS : usage of photometry catalogs

DIRECT DETECTION OF STRONG GALAXY-GALAXY LENSING IN SDSS : usage of photometry catalogs. Min-Su Shin msshin @ astro.princeton.edu Princeton University Michael Strauss, Masamune Oguri, Naohisa Inada, and other SDSS people. Discovery of strongly lensed galaxies.

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DIRECT DETECTION OF STRONG GALAXY-GALAXY LENSING IN SDSS : usage of photometry catalogs

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  1. DIRECT DETECTION OF STRONG GALAXY-GALAXY LENSING IN SDSS: usage of photometry catalogs Min-Su Shin msshin @ astro.princeton.edu Princeton University Michael Strauss, Masamune Oguri, Naohisa Inada, and other SDSS people

  2. Discovery of strongly lensed galaxies • Increasing number of deep wide-field surveys • Single or multi-band imaging • Eye-ball check of arc-like objects on images • e.g. Hennawi et al. 2006 • Using image analysis program • e.g. Estrada et al. 2007 • Exploiting a photometry catalog

  3. Efficient usage of multi-band images • Multi-band images can be used to identify a specific kind of SED. • Photometric redshift is useful information in estimating rough distances to objects. • Compilation of multi-band data. • High-resolution IR and optical data

  4. Properties of typical galaxy strong lensing • A background galaxy is lensed by a foreground elliptical galaxy. • Forming multiple images of arc and knots. Different SED at high-z Red galaxy SED at low-z

  5. Goto et al. 2002 Selection of strong lensing candidates (1) • A typical color of ellipticals as lens galaxies is assumed in SDSS g-r and r-i: -0.2 < (r-i) – 0.25 (g-r) – 0.18 < 0.2 0.2 < (g-r) < 2.0 • We consider only quadruple systems. • The angular separation between one image and another image is < 160.0 degree when there are at least two images within a fixed radius range (1.2 – 6.0") around a possible lens galaxy.

  6. Selection of strong lensing candidates (2) Example of expected candidates SLACS : HST ACS image of SDSS J0737+3216 • Colors of the two possible lens images have to be different from that of the lens galaxy in at least one of four colors, i.e. Δcolor > 2.0. • Main contamination of galaxy group or clusters Finding the candidates that satisfy the criteria.

  7. Discovery of our lensed E+A galaxy • Δ(u – g) > 2.0 and angle < 160.0 degree. • Galaxy cluster? zlens = 0.349 zsource = 0.766

  8. Follow-up observations MgII λλ2796, 2803 outflow gas velocity? (Tremonti et al. 2007) complex source morphology? 4th image? Subaru and APO 3.5m

  9. Keck LRIS E+A galaxy z=0.727 z=1.86 z~0.35 UH88 z=0.021 LBG z=2.165 z=0.41 UH88 z~0.4 Other confirmed lenses

  10. Ongoing works • Refining the selection criteria: • Color of lens galaxies → late-type lens galaxies? • Color difference cut → Δcolor > 1.0 • Double lens images → 160.0 < angle < 180.0 deg. • Single magnified z > 2.0 galaxy • Radial arc → several objects on the same side with a narrow angle • Distance cut → lens galaxy cluster or group • Follow-up observations of some selected candidates. • We will submit the paper to explain the selection method, the discovery of the E+A lensed galaxy, and its MgII absorption feature this month.

  11. Summary • Selection criteria : relative positions of lens images, color difference between lens and images, and the number of possible lens images. • Efficient detection of faint lens images even though the images do not show a bright arc. → finding a high-z lensed galaxy • Application to the compiled multi-band photometry catalog from wide-field imaging surveys in VO environment. • Computationally less expensive than direct image analysis. • Using both our selection method and a direct image analysis might be the best way to find all kinds of lensing.

  12. SDSS HST WFPC2 “Partial answers are the only answers.” - James Gunn z=1.554 Sand, Treu, Ellis, and Smith, ApJ, 627, 32, 2005 Examples

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