The 8 o'clock Arc: A Serendipitous Discovery of a Strongly Lensed Lyman Break Galaxy in the SDSS DR4 Imaging Data

We report on the serendipitous discovery of the brightest Lyman Break Galaxy (LBG) currently known, a galaxy at z=2.73 that is being strongly lensed by the z=0.38 Luminous Red Galaxy (LRG) SDSS J002240.91+143110.4. The arc of this gravitational lens system, which we have dubbed the "8 o'clock arc" due to its time of discovery, was initially identified in the imaging data of the Sloan Digital Sky Survey Data Release 4 (SDSS DR4); followup observations on the Astrophysical Research Consortium (ARC) 3.5m telescope at Apache Point Observatory confirmed the lensing nature of this system and led to the identification of the arc's spectrum as that of an LBG. The arc has a spectrum and a redshift remarkably similar to those of the previous record-holder for brightest LBG (MS 1512-cB58, a.k.a "cB58"), but, with an estimated total magnitude of (g,r,i) = (20.0,19.2,19.0) and surface brightness of (mu_g,mu_r,mu_i) = (23.3, 22.5, 22.3) mag/arcsec^2, the 8 o'clock arc is thrice as bright. The 8 o'clock arc, which consists of three lensed images of the LBG, is 162deg (9.6arcsec) long and has a length-to-width ratio of 6:1. A fourth image of the LBG -- a counter-image -- can also be identified in the ARC 3.5m g-band images. A simple lens model for the system assuming a singular isothermal ellipsoid potential yields an Einstein radius of 2.91+/-0.14 arcsec, a total mass for the lensing LRG (within the (10.6+/-0.5)/h kpc enclosed by the lensed images) of 1.04x10^12/h Msun, and a magnification factor for the LBG of 12.3(+15/-3.6). The LBG itself is intrinsically quite luminous (approximately 6L*) and shows indications of massive recent star formation, perhaps as high as 160/h Msun/year.Comment: 4 pages 5 figures, submitted to ApJ Letter

The Cut & Enhance method : selecting clusters of galaxies from the SDSS commissioning data

We describe an automated method, the Cut & Enhance method (CE) for detecting clusters of galaxies in multi-color optical imaging surveys. This method uses simple color cuts, combined with a density enhancement algorithm, to up-weight pairs of galaxies that are close in both angular separation and color. The method is semi-parametric since it uses minimal assumptions about cluster properties in order to minimize possible biases. No assumptions are made about the shape of clusters, their radial profile or their luminosity function. The method is successful in finding systems ranging from poor to rich clusters of galaxies, of both regular and irregular shape. We determine the selection function of the CE method via extensive Monte Carlo simulations which use both the real, observed background of galaxies and a randomized background of galaxies. We use position shuffled and color shuffled data to perform the false positive test. We have also visually checked all the clusters detected by the CE method. We apply the CE method to the 350 deg^2 of the SDSS (Sloan Digital Sky Survey) commissioning data and construct a SDSS CE galaxy cluster catalog with an estimated redshift and richness for each cluster. The CE method is compared with other cluster selection methods used on SDSS data such as the Matched Filter (Postman et al. 1996, Kim et al. 2001), maxBCG technique (Annis et al. 2001) and Voronoi Tessellation (Kim et al. 2001). The CE method can be adopted for cluster selection in any multi-color imaging surveys.Comment: 62 pages, 32 figures, Accepted for publication in the Astronomical Journal, "the CE galaxy cluster catalog can be downloaded from, http://astrophysics.phys.cmu.edu/~tomo/ce/

The Sloan Bright Arcs Survey : Six Strongly Lensed Galaxies at z=0.4-1.4

We present new results of our program to systematically search for strongly lensed galaxies in the Sloan Digital Sky Survey (SDSS) imaging data. In this study six strong lens systems are presented which we have confirmed with follow-up spectroscopy and imaging using the 3.5m telescope at the Apache Point Observatory. Preliminary mass models indicate that the lenses are group-scale systems with velocity dispersions ranging from 466-878 km s^{-1} at z=0.17-0.45 which are strongly lensing source galaxies at z=0.4-1.4. Galaxy groups are a relatively new mass scale just beginning to be probed with strong lensing. Our sample of lenses roughly doubles the confirmed number of group-scale lenses in the SDSS and complements ongoing strong lens searches in other imaging surveys such as the CFHTLS (Cabanac et al 2007). As our arcs were discovered in the SDSS imaging data they are all bright ($r\lesssim22$), making them ideally suited for detailed follow-up studies.Comment: 13 pages, 3 figures, submitted to ApJL, the Sloan Bright Arcs page is located here: http://home.fnal.gov/~kubo/brightarcs.htm

The Sloan Bright Arcs Survey: Four Strongly Lensed Galaxies with Redshift >2

We report the discovery of four very bright, strongly-lensed galaxies found via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and 6. These were followed-up with spectroscopy and imaging data from the Astrophysical Research Consortium 3.5m telescope at Apache Point Observatory and found to have redshift $z>2.0$. With isophotal magnitudes $r = 19.2 - 20.4$ and 3\arcsec-diameter magnitudes $r = 20.0 - 20.6$, these systems are some of the brightest and highest surface brightness lensed galaxies known in this redshift range. In addition to the magnitudes and redshifts, we present estimates of the Einstein radii, which range from 5.0 \arcsec to 12.7 \arcsec, and use those to derive the enclosed masses of the lensing galaxies

Interactions of thrombospondins with α4β1 integrin and CD47 differentially modulate T cell behavior

Thrombospondin (TSP)-1 has been reported to modulate T cell behavior both positively and negatively. We found that these opposing responses arise from interactions of TSP1 with two different T cell receptors. The integrin α4β1 recognizes an LDVP sequence in the NH2-terminal domain of TSP1 and was required for stimulation of T cell adhesion, chemotaxis, and matrix metalloproteinase gene expression by TSP1. Recognition of TSP1 by T cells depended on the activation state of α4β1 integrin, and TSP1 inhibited interaction of activated α4β1 integrin on T cells with its counter receptor vascular cell adhesion molecule-1. The α4β1 integrin recognition site is conserved in TSP2. A recombinant piece of TSP2 containing this sequence replicated the α4β1 integrin–dependent activities of TSP1. The β1 integrin recognition sites in TSP1, however, were neither necessary nor sufficient for inhibition of T cell proliferation and T cell antigen receptor signaling by TSP1. A second TSP1 receptor, CD47, was not required for some stimulatory responses to TSP1 but played a significant role in its T cell antigen receptor antagonist and antiproliferative activities. Modulating the relative expression or function of these two TSP receptors could therefore alter the direction or magnitude of T cell responses to TSPs

Merging Galaxies in the SDSS EDR

We present a new catalog of merging galaxies obtained through an automated systematic search routine. The 1479 new pairs of merging galaxies were found in approximately 462 sq deg of the Sloan Digital Sky Survey Early Data Release (SDSS EDR; Stoughton et al. 2002) photometric data, and the pair catalog is complete for galaxies in the magnitude range 16.0 <= g* <= 20. The selection algorithm, implementing a variation on the original Karachentsev (1972) criteria, proved to be very efficient and fast. Merging galaxies were selected such that the inter-galaxy separations were less than the sum of the component galaxies' radii. We discuss the characteristics of the sample in terms of completeness, pair separation, and the Holmberg effect. We also present an online atlas of images for the SDSS EDR pairs obtained using the corrected frames from the SDSS EDR database. The atlas images also include the relevant data for each pair member. This catalog will be useful for conducting studies of the general characteristics of merging galaxies, their environments, and their component galaxies. The redshifts for a subset of the interacting and merging galaxies and the distribution of angular sizes for these systems indicate the SDSS provides a much deeper sample than almost any other wide-area catalog to date.Comment: 58 pages, which includes 15 figures and 6 tables. Figures 2, 8, 9, 10, 11, 13, and 14 are provided as JPEG files. For online atlas, see http://home.fnal.gov/~sallam/MergePair/ . Accepted for publication in A

Discovery of A Very Bright, Strongly-Lensed z=2 Galaxy in the SDSS DR5

We report on the discovery of a very bright z = 2.00 star-forming galaxy that is strongly lensed by a foreground z=0.422 luminous red galaxy (LRG). This system was found in a systematic search for bright arcs lensed by LRGs and brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 5 sample. Follow-up observations on the Subaru 8.2m telescope on Mauna Kea and the Astrophysical Research Consortium 3.5m telescope at Apache Point Observatory confirmed the lensing nature of this system. A simple lens model for the system, assuming a singular isothermal ellipsoid mass distribution, yields an Einstein radius of 3.82 +/- 0.03 arcsec or 14.8 +/- 0.1 kpc/h at the lens redshift. The total projected mass enclosed within the Einstein radius is 2.10 +/- 0.03 x 10^12 M_sun/h, and the magnification factor for the source galaxy is 27 +/- 1. Combining the lens model with our gVriz photometry, we find an (unlensed) star formation rate for the source galaxy of 32 M_sun/h / yr, adopting a fiducial constant star formation rate model with an age of 100 Myr and E(B-V) = 0.25. With an apparent magnitude of r = 19.9, this system is among the very brightest lensed z >= 2 galaxies, and provides an excellent opportunity to pursue detailed studies of the physical properties of an individual high-redshift star-forming galaxy.Comment: 31 pages, 12 figures, 4 tables, submitted to Ap

High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data II: The Spring Equatorial Stripe

This is the second paper in a series aimed at finding high-redshift quasars from five-color (u'g'r'i'z') imaging data taken along the Celestial Equator by the Sloan Digital Sky Survey (SDSS) during its commissioning phase. In this paper, we present 22 high-redshift quasars (z>3.6) discovered from ~250 deg^2 of data in the spring Equatorial Stripe, plus photometry for two previously known high-redshift quasars in the same region of sky. Our success rate of identifying high-redshift quasars is 68%. Five of the newly discovered quasars have redshifts higher than 4.6 (z=4.62, 4.69, 4.70, 4.92 and 5.03). All the quasars have i* < 20.2 with absolute magnitude -28.8 < M_B < -26.1 (h=0.5, q_0=0.5). Several of the quasars show unusual emission and absorption features in their spectra, including an object at z=4.62 without detectable emission lines, and a Broad Absorption Line (BAL) quasar at z=4.92.Comment: 28 pages, AJ in press (Jan 2000), final version with minor changes; high resolution finding charts available at http://www.astro.princeton.edu/~fan/paper/qso2.htm

The Angular Correlation Function of Galaxies from Early SDSS Data

The Sloan Digital Sky Survey is one of the first multicolor photometric and spectroscopic surveys designed to measure the statistical properties of galaxies within the local Universe. In this Letter we present some of the initial results on the angular 2-point correlation function measured from the early SDSS galaxy data. The form of the correlation function, over the magnitude interval 18<r*<22, is shown to be consistent with results from existing wide-field, photographic-based surveys and narrower CCD galaxy surveys. On scales between 1 arcminute and 1 degree the correlation function is well described by a power-law with an exponent of ~ -0.7. The amplitude of the correlation function, within this angular interval, decreases with fainter magnitudes in good agreement with analyses from existing galaxy surveys. There is a characteristic break in the correlation function on scales of approximately 1-2 degrees. On small scales, < 1', the SDSS correlation function does not appear to be consistent with the power-law form fitted to the 1'< theta <0.5 deg data. With a data set that is less than 2% of the full SDSS survey area, we have obtained high precision measurements of the power-law angular correlation function on angular scales 1' < theta < 1 deg, which are robust to systematic uncertainties. Because of the limited area and the highly correlated nature of the error covariance matrix, these initial results do not yet provide a definitive characterization of departures from the power-law form at smaller and larger angles. In the near future, however, the area of the SDSS imaging survey will be sufficient to allow detailed analysis of the small and large scale regimes, measurements of higher-order correlations, and studies of angular clustering as a function of redshift and galaxy type