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: 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


Efficient usage of multi-band images: 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


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


Selection of strong lensing candidates (1): 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 andlt; (r-i) – 0.25 (g-r) – 0.18 andlt; 0.2 0.2 andlt; (g-r) andlt; 2.0 We consider only quadruple systems. The angular separation between one image and another image is andlt; 160.0 degree when there are at least two images within a fixed radius range (1.2 – 6.0') around a possible lens galaxy.


Selection of strong lensing candidates (2): Selection of strong lensing candidates (2) 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 andgt; 2.0. Main contamination of galaxy group or clusters Example of expected candidates SLACS : HST ACS image of SDSS J0737+3216 Finding the candidates that satisfy the criteria.


Discovery of our lensed E+A galaxy: Discovery of our lensed E+A galaxy Δ(u – g) andgt; 2.0 and angle andlt; 160.0 degree. Galaxy cluster? zlens = 0.349 zsource = 0.766


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


Other confirmed lenses: Other confirmed lenses


Ongoing works: Ongoing works Refining the selection criteria: Color of lens galaxies → late-type lens galaxies? Color difference cut → Δcolor andgt; 1.0 Double lens images → 160.0 andlt; angle andlt; 180.0 deg. Single magnified z andgt; 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.


Summary: 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.


Examples: Examples