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Register a new userDiscovery of A Very Bright, Strongly-Lensed z=2 Galaxy in the SDSS DR5
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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.
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Using HST and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z~7.6 in the field of the massive galaxy cluster Abell 1689. The galaxy candidate, which we refer to as A1689-zD1, shows a strong z-J break of at least 2.2 mag and is completely undetected (<1 sigma) in HST/ACS g, r, i, and z-band data. These properties, combined with the very blue J-H and H-[4.5] colors, are exactly the properties of an z~7.6 LBG and can only be reasonably fit by a star-forming galaxy at z=7.6 +/- 0.4. Attempts to reproduce these properties with a model galaxy at z<4 yield particularly poor fits. A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 sigma) in the NICMOS H band and is ~1.3 mag brighter than the brightest-known z-dropout galaxy. When corrected for the cluster magnification of 9.3 at z~7.6, the candidate has an intrinsic magnitude of H=27.1 AB, or about an L* galaxy at z~7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size ~<300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9) x 10^9 M_sun, stellar ages 45-320 Myr, star-formation rates ~<7.6 M_sun/yr, and low reddening with A_V <= 0.3. These properties are generally similar to those of LBGs found at z~5-6. The inferred stellar ages suggest a formation redshift of z~8-10 (t~<0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z>7.0 galaxy candidate found to date.
We present the first result of a survey for strong galaxy-galaxy lenses in Sloan Digital Sky Survey (SDSS) images. SDSS J082728.70+223256.4 was selected as a lensing candidate using selection criteria based on the color and positions of objects in the SDSS photometric catalog. Follow-up imaging and spectroscopy showed this object to be a lensing system. The lensing galaxy is an elliptical at z = 0.349 in a galaxy cluster. The lensed galaxy has the spectrum of a post-starburst galaxy at z = 0.766. The lensing galaxy has an estimated mass of $sim 1.2 times 10^{12} M_{odot}$ and the corresponding mass to light ratio in the B-band is $sim 26 M_{odot}/L_{odot}$ inside 1.1 effective radii of the lensing galaxy. Our study shows how catalogs drawn from multi-band surveys can be used to find strong galaxy-galaxy lenses having multiple lens images. Our strong lensing candidate selection based on photometry-only catalogs will be useful in future multi-band imaging surveys such as SNAP and LSST.
We report the discovery of a very bright (r = 20.16), highly magnified, and yet intrinsically very luminous Ly{alpha} emitter (LAE) at z = 2.82. This system comprises four images in the observer plane with a maximum separation of ~ 6 and it is lensed by a z = 0.55 massive early-type galaxy. It was initially identified in the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey for GALaxy-Ly{alpha} EmitteR sYstems (BELLS GALLERY) survey, and follow-up imaging and spectroscopic observations using the Gran Telescopio Canarias (GTC) and William Herschel Telescope (WHT) confirmed the lensing nature of this system. A lens model using a singular isothermal ellipsoid in an external shear field reproduces quite well the main features of the system, yielding an Einstein radius of 2.95 +/- 0.10, and a total magnification factor for the LAE of 8.8 +/- 0.4. This LAE is one of the brightest and most luminous galaxy-galaxy strong lenses known. We present initial imaging and spectroscopy showing the basic physical and morphological properties of this lensed system.
We report the discovery of seven new, very bright gravitational lens systems from our ongoing gravitational lens search, the Sloan Bright Arcs Survey (SBAS). Two of the systems are confirmed to have high source redshifts z=2.19 and z=2.94. Three other systems lie at intermediate redshift with z=1.33,1.82,1.93 and two systems are at low redshift z=0.66,0.86. The lensed source galaxies in all of these systems are bright, with i-band magnitudes ranging from 19.73-22.06. We present the spectrum of each of the source galaxies in these systems along with estimates of the Einstein radius for each system. The foreground lens in most systems is identified by a red sequence based cluster finder as a galaxy group; one system is identified as a moderately rich cluster. In total the SBAS has now discovered 19 strong lens systems in the SDSS imaging data, 8 of which are among the highest surface brightness zsimeq2-3 galaxies known.
We report the discovery of a z_{phot}=6.18^{+0.05}_{-0.07} (95% confidence level) dwarf galaxy, lensed into four images by the galaxy cluster MACS J0329.6-0211 (z_{l}=0.45). The galaxy is observed as a high-redshift dropout in HST/ACS/WFC3 CLASH and Spitzer/IRAC imaging. Its redshift is securely determined due to a clear detection of the Lyman-break in the 18-band photometry, making this galaxy one of the highest-redshift multiply-lensed objects known to date with an observed magnitude of F125W=24.00pm0.04 AB mag for its highest-magnified image. We also present the first strong-lensing analysis of this cluster uncovering 15 additional multiply-imaged candidates of five lower-redshift sources spanning the range z_{s}~2-4. The mass model independently supports the high photometric redshift and reveals magnifications of 11.6^{+8.9}_{-4.1}, 17.6^{+6.2}_{-3.9}, 3.9^{+3.0}_{-1.7}, and 3.7^{+1.3}_{-0.2}, respectively, for the four images of the high-redshift galaxy. With this we construct a source image with a physical resolution of ~200 pc when the universe was ~0.9 Gyr old, where the z~6.2 galaxy occupies a source-plane area of approximately 2.2 kpc^{2}. Modeling the observed spectral energy distribution using population synthesis models, we find a demagnified stellar mass of ~10^{9} {M}_{sun}, subsolar metallicity (Z/Z_{sun}~0.5), low dust content (A_{V}~0.1 mag), a demagnified star formation rate (SFR) of ~3.2 {M}_{sun} yr^{-1}, and a specific SFR of ~3.4 Gyr^{-1}, all consistent with the properties of local dwarf galaxies.
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