[en] 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 followup 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 ≅ 22), making them ideally suited for detailed follow-up studies

[en] 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 3.5 m telescope at the Apache Point Observatory. Preliminary mass models indicate that the lenses are group-scale systems with velocity dispersions ranging from 464 to 882 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. As our arcs were discovered in the SDSS imaging data they are all bright (r ∼< 22), making them ideally suited for detailed follow-up studies.

[en] 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 3.5 m telescope at Apache Point Observatory and found to have redshift z > 2.0. With isophotal magnitudes r = 19.2-20.4 and 3'' 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 to 12.''7, and use those to derive the enclosed masses of the lensing galaxies.

[en] We present measurements of two types of cluster galaxy alignments based on a volume limited and highly pure (≥90%) sample of clusters from the GMBCG catalog derived from Data Release 7 of the Sloan Digital Sky Survey (SDSS DR7). We detect a clear brightest cluster galaxy (BCG) alignment (the alignment of major axis of the BCG toward the distribution of cluster satellite galaxies). We find that the BCG alignment signal becomes stronger as the redshift and BCG absolute magnitude decrease and becomes weaker as BCG stellar mass decreases. No dependence of the BCG alignment on cluster richness is found. We can detect a statistically significant (≥3σ) satellite alignment (the alignment of the major axes of the cluster satellite galaxies toward the BCG) only when we use the isophotal fit position angles (P.A.s), and the satellite alignment depends on the apparent magnitudes rather than the absolute magnitudes of the BCGs. This suggests that the detected satellite alignment based on isophotal P.A.s from the SDSS pipeline is possibly due to the contamination from the diffuse light of nearby BCGs. We caution that this should not be simply interpreted as non-existence of the satellite alignment, but rather that we cannot detect them with our current photometric SDSS data. We perform our measurements on both SDSS r-band and i-band data, but do not observe a passband dependence of the alignments.

[en] We describe 10 strong lensing galaxy clusters of redshift 0.26 ≤ z ≤ 0.56 that were found in the Sloan Digital Sky Survey. We present measurements of richness (N₂₀₀), mass (M₂₀₀), and velocity dispersion for the clusters. We find that in order to use the mass-richness relation from Johnston et al., which was established at mean redshift of 0.25, it is necessary to scale measured richness values up by 1.47. Using this scaling, we find richness values for these clusters to be in the range of 22 ≤ N₂₀₀ ≤ 317 and mass values to be in the range of 1 × 10¹⁴ h ^–1 M_☉ ≤ M₂₀₀ ≤ 30 × 10¹⁴ h ^–1 M_☉. We also present measurements of Einstein radius, mass, and velocity dispersion for the lensing systems. The Einstein radii (θ_E) are all relatively small, with 5.''4 ≤ θ_E ≤ 13''. Finally, we consider if there is evidence that our clusters are more concentrated than ΛCDM would predict. We find that six of our clusters do not show evidence of overconcentration, while four of our clusters do. We note a correlation between overconcentration and mass, as the four clusters showing evidence of overconcentration are all lower-mass clusters. For the four lowest mass clusters the average value of the concentration parameter c₂₀₀ is 11.6, while for the six higher-mass clusters the average value of c₂₀₀ is 4.4. ΛCDM would place c₂₀₀ between 3.4 and 5.7.

[en] 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 to 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, SBAS has now discovered 19 strong lens systems in the SDSS imaging data, 8 of which are among the highest surface brightness z ≅ 2-3 galaxies known.

[en] Stripe 82 in the Sloan Digital Sky Survey was observed multiple times, allowing deeper images to be constructed by co-adding the data. Here, we analyze the ellipticities of background galaxies in this 275 deg² region, searching for evidence of distortions due to cosmic shear. We do so using measurements of both the shear-shear correlation function and power spectrum, with the latter determined using both ''quadratic'' and ''pseudo'' estimation techniques. We show how we verified these methods using mock catalogs. We also describe our methods for modeling and correcting for the effects of the point-spread function (PSF) in our shape measurements, and we also describe our prescription for estimating photometric redshifts (photo-z's) for our galaxy sample. In particular, we assess the impact of potential systematic effects due to the PSF and to photo-z's, and show that these are under control in our analysis. We find consistent correlation function and power spectrum results, where the E-mode cosmic shear signal is detected in both real and Fourier space with >5σ significance on degree scales, while the B-mode is consistent with zero as expected. The amplitude of the signal constrains the combination of the matter density Ω_m and fluctuation amplitude σ₈ to be Ω^0.7_mσ₈ = 0.252^+0.032_–0.052.

[en] We present a regularized maximum likelihood weak-lensing reconstruction of the Deep Lens Survey F2 field (4 deg²). High signal-to-noise ratio peaks in our lensing significance map appear to be associated with possible projected filamentary structures. The largest apparent structure extends for over a degree in the field and has contributions from known optical clusters at three redshifts (z ∼ 0.3, 0.43, 0.5). Noise in weak-lensing reconstructions is known to potentially cause 'false positives'; we use Monte Carlo techniques to estimate the contamination in our sample, and find that 10%-25% of the peaks are expected to be false detections. For significant lensing peaks, we estimate the total signal-to-noise ratio of detection using a method that accounts for pixel-to-pixel correlations in our reconstruction. We also report the detection of a candidate relative underdensity in the F2 field with a total signal-to-noise ratio of ∼5.5.

[en] 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), SDSS J120602.09+514229.5. This system, nicknamed the 'Clone', 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 8.2 m telescope on Mauna Kea and the Astrophysical Research Consortium 3.5 m 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 θ_Ein = 3.82 ± 0.''03 or 14.8 ± 0.1 h^-1 kpc at the lens redshift. The total projected mass enclosed within the Einstein radius is 2.10 ± 0.03 x 10¹² h ^-1 M_sun, and the magnification factor for the source galaxy is 27 ± 1. Combining the lens model with our gVriz photometry, we find a (unlensed) star formation rate (SFR) for the source galaxy of 32 h^-1 M _sun yr^-1, adopting a fiducial constant SFR model with an age of 100 Myr and E(B - V) = 0.25. With an apparent magnitude of r = 19.8, 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.

[en] We describe and present initial results of a weak lensing survey of nearby (z ∼< 0.1) galaxy clusters in the Sloan Digital Sky Survey (SDSS). In this first study, galaxy clusters are selected from the SDSS spectroscopic galaxy cluster catalogs of Miller et al. and Berlind et al. We report a total of seven individual low-redshift cluster weak lensing measurements that include A2048, A1767, A2244, A1066, A2199, and two clusters specifically identified with the C4 algorithm. Our program of weak lensing of nearby galaxy clusters in the SDSS will eventually reach ∼200 clusters, making it the largest weak lensing survey of individual galaxy clusters to date.