Sloan Digital Sky Survey Imaging Data Research Articles

A Detailed Morphological and Spectroscopic Study of Merging Dwarf Galaxy PGC 030133

We present a detailed morphology and spectroscopic study of a merging dwarf galaxy PGC 030133. Using the publicly available fiber spectroscopic data from the Sloan Digital Sky Survey (SDSS), we analyzed nine-strong emission lines of wavelength range 4336 Å to 6739 Å. We find that the strongest emission line is OIII5007, with an intensity of 146.32 × 10-17 erg/s/cm2 /Å. The observed emission lines are well fitted with a Gaussian profile with a coefficient of regression greater than 96%, and the derived full-width half maximum (FWHM) is less than 4.2Å. The Balmer decrement, characterized by the line ratio between Hα and Hβ is 3.07, suggesting a presence of dust at the center of PGC 030133. We derived the star-formation rate and emission line metallicity of PGC 030133 using extinction corrected emission line fluxes. SFR derived from Hα emission line flux is 0.0033 Mʘyear-1 and emission line metallicity derived from flux ratio between NII and Hα is 8.13 dex. Using the SDSS, g, and z-band imaging data, we derived morphological parameters. PGC 030133 has a half-light radius of 3.38 arc second and 3.05 arc second in g-band and z-band respectively and observed one-dimensional light profile is well fitted with a Sersic function with near exponential Sersic index ~ 0.9.

Seeing in the dark – II. Cosmic shear in the Sloan Digital Sky Survey

Statistical weak lensing by large-scale structure – cosmic shear – is a promising cosmological tool, which has motivated the design of several large upcoming surveys. Here, we present a measurement of cosmic shear using co-added Sloan Digital Sky Survey (SDSS) imaging in 168 square degrees of the equatorial region, with r < 23.5 and i < 22.5, a source number density of 2.2 per arcmin^2 and mean redshift of z_(med) = 0.52. These co-adds were generated using a new method described in the companion Paper I that was intended to minimize systematic errors in the lensing measurement due to coherent point spread function anisotropies that are otherwise prevalent in the SDSS imaging data. We present measurements of cosmic shear out to angular separations of 2°, along with systematics tests that (combined with those from Paper I on the catalogue generation) demonstrate that our results are dominated by statistical rather than systematic errors. Assuming a cosmological model corresponding to Wilkinson Microwave Anisotropy Probe 7(WMAP7) and allowing only the amplitude of matter fluctuations σ_8 to vary, we find a best-fitting value of σ_8=0.636^(+0.109)_(−0.154) (1σ); without systematic errors this would be σ_8=0.636^(+0.099)_(−0.137) (1σ). Assuming a flat Λ cold dark matter model, the combined constraints with WMAP7 are σ_8=0.784^(+0.028)_(−0.026)(1σ)^(+0.055)_(−0.054)(2σ) and Ω_mh^2=0.1303^(+0.0047)_(−0.0048)(1σ)^(+0.009)_(−0.009)(2σ); the 2σ error ranges are, respectively, 14 and 17 per cent smaller than WMAP7 alone.

Separating intrinsic alignment and galaxy-galaxy lensing

The coherent physical alignment of galaxies is an important systematic for gravitational lensing studies as well as a probe of the physical mechanisms involved in galaxy formation and evolution. We develop a formalism for treating this intrinsic alignment (IA) in the context of galaxy-galaxy lensing and present an improved method for measuring IA contamination, which can arise when sources physically associated with the lens are placed behind the lens due to photometric redshift scatter. We apply the technique to recent Sloan Digital Sky Survey (SDSS) measurements of Luminous Red Galaxy lenses and typical ( ∼ L*) source galaxies with photometric redshifts selected from the SDSS imaging data. Compared to previous measurements, this method has the advantage of being fully self-consistent in its treatment of the IA and lensing signals, solving for the two simultaneously. We find an IA signal consistent with zero, placing tight constraints on both the magnitude of the IA effect and its potential contamination to the lensing signal. While these constraints depend on source selection and redshift quality, the method can be applied to any measurement that uses photometric redshifts. We obtain a model-independent upper-limit of roughly 10% IA contamination for projected separations of rp ≈ 0.1–10 h−1Mpc. With more stringent photo-z cuts and reasonable assumptions about the physics of intrinsic alignments, this upper limit is reduced to 1–2%. These limits are well below the statistical error of the current lensing measurements. Our results suggest that IA will not present intractable challenges to the next generation of galaxy-galaxy lensing experiments, and the methods presented here should continue to aid in our understanding of alignment processes and in the removal of IA from the lensing signal.

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.

Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. I. Crowded‐Field Photometry and Cluster Fiducial Sequences inugriz

We present photometry for globular and open cluster stars observed with the Sloan Digital Sky Survey (SDSS). In order to exploit the over 100 million stellar objects with -->r < 22.5 mag observed by SDSS, we need to understand the characteristics of stars in the SDSS ugriz filters. While star clusters provide important calibration samples for stellar colors, the regions close to globular clusters, where the fraction of field stars is smallest, are too crowded for the standard SDSS photometric pipeline to process. To complement the SDSS imaging survey, we reduce the SDSS imaging data for crowded cluster fields using the DAOPHOT/ALLFRAME suite of programs and present photometry for 17 globular clusters and three open clusters in a SDSS value-added catalog. Our photometry and cluster fiducial sequences are on the native SDSS 2.5 m ugriz photometric system, and the fiducial sequences can be directly applied to the SDSS photometry without relying on any transformations. Model photometry for red giant branch and main-sequence stars obtained by Girardi et al. cannot be matched simultaneously to fiducial sequences; their colors differ by ~0.02-0.05 mag. Good agreement (0.02 mag in colors) is found with Clem et al. empirical fiducial sequences in u'g'r'i'z' when using the transformation equations in Tucker et al.

E+A and companion galaxies - I. A catalogue and statistics

Based on our intensive spectroscopic campaign with the GoldCam spectrograph on the Kitt Peak National Observatory (KPNO) 2.1-m telescope, we have constructed the first catalogue of E+A galaxies with spectroscopic companion galaxies, and investigated a probability that an E+A galaxy has close companion galaxies. We selected 660 E+A galaxies with 4.0 A < Hδ EW at a redshift of <0.167 from the Data Release 5 of the Sloan Digital Sky Survey (SDSS). We selected their companion candidates from the SDSS imaging data, and classified them into true companions, fore/background galaxies and companion candidates using the SDSS and our KPNO spectra. We observed 26 companion candidates of E+A galaxies at the KPNO to measure their redshifts. Their spectra showed that 17 targets are true companion galaxies. The number of spectroscopically confirmed E+A's companions is now 34. This becomes the first catalogue of E+A galaxies with spectroscopic companion systems. We found that E+A galaxies have 54 per cent larger probability of having companion galaxies (7.88 per cent) as compared to the comparison sample of normal galaxies (5.12 per cent). A statistical test shows that the probabilities are different with 99.7 per cent significance. Our results based on spectroscopy tighten the connection between the dynamical merger/interaction and the origin of E+A galaxies.

The color excess of quasars with intervening DLA systems

We analyzed the spectroscopic and photometric database of the 5th data release of the Sloan Digital Sky Survey (SDSS) to search for evidence of the quasar reddening produced by dust embedded in intervening damped Ly α (DLA) systems. From a list of 5164 quasars in the interval of emission redshift and SDSS spectra with signal-to-noise ratio SNR 4, we built up an “absorption sample” of 248 QSOs with a single DLA system in the interval of absorption redshift and a “pool” of 1959 control QSOs without DLA systems or strong metal systems. For each QSO of the absorption sample we extracted from the pool a subset of control QSOs that are closest in redshift and magnitude. The mean color of this subset was used as a zero point to measure the “deviation from the mean color” of individual DLA-QSOs, . The colors were measured using “BEST” ugriz SDSS imaging data. The mean color excess of the absorption sample, , was estimated by averaging the individual color deviations . We find = 27 (± 9)10-3 mag and = 54 (± 12)10-3 mag. These values are representative of the reddening of DLA systems at za ≈ 2.7 in SDSS QSOs with limiting magnitude r 20.2. The detection of the mean reddening is confirmed by several statistical tests. Analysis of the results suggests an origin of the reddening in dust embedded in the DLA systems, with an SMC-type extinction curve. By converting the reddening into rest-frame extinction, we derive a mean dust-to-gas ratio 2 to 410-23 mag cm2. This value is -1.25 dex lower than the mean dust-to-gas ratio of the Milky Way, in line with the lower level of metallicity in the present DLA sample.

WHITE DWARF LUMINOSITY AND MASS FUNCTIONS FROM SLOAN DIGITAL SKY SURVEY SPECTRA

We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine the completeness of the SDSS spectroscopic WD sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g − i) and apparent magnitude (g) that covers the range −1.0 < g − i < 0.2 and 15 < g < 19.5. We address the observed upturn in log g for WDs with T eff 12,000 K and offer arguments that the problem is limited to the line profiles and is not present in the continuum. We offer an empirical method of removing the upturn, recovering a reasonable mass function for WDs with T eff< 12,000 K. Finally, we present a WD LF with nearly an order of magnitude (3358) more spectroscopically confirmed WDs than any previous work.

Morphological Dependence of Star Formation Properties for the Galaxies in the Merging Galaxy Cluster A2255

The merging cluster of galaxies A2255 is covered by the Sloan Digital Sky Survey (SDSS) survey. In this paper we perform a morphological classification on the basis of the SDSS imaging and spectral data, and investigate the morphological dependence of the star formation rates (SFRs) for these member galaxies. As we expect, a tight correlation between the normalized SFR by stellar mass (SFR/M$_*$) and the H$\alpha$ equivalent width is found for the late-type galaxies in A2255. The correlation of SFR/M$_*$ with the continuum break strength at 4000 \AA is also confirmed. The SFR/M$_*$ - M$_*$ correlation is found for both the early- and late-type galaxies, indicating that the star formation activity tends to be suppressed when the assembled stellar mass M$_*$) increases, and this correlation is tighter and steeper for the late-type cluster galaxies. Compared with the mass range of field spiral galaxies, only two massive late-type galaxies with M$_*>10^{11}$ M$_{\odot}$ are survived in A2255, suggesting that the gas disks of massive spiral galaxies could have been tidally stripped during cluster formation. Additionally, the SFR variation with the projected radial distance are found to be heavily dependent upon galaxy morphology: the early-type galaxies have a very weak inner decrease in SFR/M$_*$, while the inner late-type galaxies tend to have higher SFR/M$_*$ values than the outer late-types. This may suggest that the galaxy-scale turbulence stimulated by the merging of subclusters might have played different roles on early- and late-type galaxies, which leads to a suppression of the star formation activity for E/S0 galaxies and a SFR enhancement for spiral and irregular galaxies.

The bright end of the luminosity function of red sequence galaxies

We study the bright end of the luminosity distribution of galaxies in fields with luminous red galaxies (LRG) from the Sloan Digital Sky Survey (SDSS). Using 2099 deg 2 of SDSS imaging data, we search for luminous (≥L*) early-type galaxies within 1.0 h -1 Mpc of a volume-limited sample of 12608 spectroscopic LRG in the redshift range 0.12 < z < 0.38. Most of these objects lie in rich environments, with the LRG being the brightest object within 1.0h -1 Mpc. The luminosity gap, M 12 , between the first- and second-ranked galaxies within 1.0h -1 Mpc is large (∼0.8 mag), substantially larger than can be explained with an exponentially decaying luminosity function of galaxies. The brightest member is less luminous (by 0.1-0.2 mag) and shows a larger gap in LRG selected groups than in cluster-like environments. The large luminosity gap shows little evolution with redshift to z = 0.4, ruling out the scenario that these LRG selected brightest cluster or group galaxies grow by recent cannibalism of cluster members.

Higher Order Moments of the Angular Distribution of Galaxies from Early Sloan Digital Sky Survey Data

We present initial results for counts in cell statistics of the angular distribution of galaxies in early data from the Sloan Digital Sky Survey (SDSS). We analyze a rectangular stripe 25 wide, covering approximately 160 deg2, containing over 106 galaxies in the apparent magnitude range 18 < r' < 22, with areas of bad seeing, contamination from bright stars, ghosts, and high galactic extinction masked out. This survey region, which forms part of the SDSS early data release, is the same as that for which two-point angular clustering statistics have recently been computed. The third and fourth moments of the cell counts, s3 (skewness) and s4 (kurtosis), constitute the most accurate measurements to date of these quantities (for r' < 21) over angular scales 0015-03. They display the approximate hierarchical scaling expected from nonlinear structure formation models and are in reasonable agreement with the predictions of Λ-dominated cold dark matter models with galaxy biasing that suppresses higher order correlations at small scales. The results are, in general, consistent with previous measurements in the APM, EDSGC, and Deeprange surveys. These results suggest that the SDSS imaging data are free of systematics to a high degree and will therefore enable determination of the skewness and kurtosis to 1% and less then 10%, as predicted earlier.

Photometric Redshifts of Quasars

We demonstrate that the design of the Sloan Digital Sky Survey (SDSS) filter system and the quality of the SDSS imaging data are sufficient for determining accurate and precise photometric redshifts of quasars. Using a sample of 2625 quasars, we show that determination is even possible for z ≤ 2.2 despite the lack of a strong continuum break, which robust photo-z techniques normally require. We find that, using our empirical method on our sample of objects known to be quasars, approximately 70% of the photometric redshifts are correct to within Δz = 0.2; the fraction of correct photometric redshifts is even better for z > 3. The accuracy of quasar photometric redshifts does not appear to be dependent upon magnitude to nearly 21st magnitude in i'. Careful calibration of the color-redshift relation to 21st magnitude may allow for the discovery of ~106 quasar candidates in addition to the 105 quasars that the SDSS will confirm spectroscopically. We discuss the efficient selection of quasar candidates from imaging data for use with the photometric redshift technique and the potential scientific uses of a large sample of quasar candidates with photometric redshifts.

High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data. VI. Sloan Digital Sky Survey Spectrograph Observations

We present data for over 100 high-redshift quasars found in ?700 deg2 by the Sloan Digital Sky Survey (SDSS), using automated selection algorithms applied to SDSS imaging data and with spectroscopic confirmation obtained during routine spectroscopic observations by the Sloan 2.5 m telescope. The SDSS spectra cover the wavelength range 3900?9200 ? at a spectral resolution of 1800 and have been obtained for 116 quasars with redshifts greater than 3.94; 92 of these objects were previously uncataloged, significantly increasing the current tally of published z > 4 quasars. The paper also reports observations of seven additional new z > 4 quasars; all were selected from the SDSS imaging survey and spectroscopically confirmed with observations by the Apache Point Observatory's 3.5 m telescope or the Hobby-Eberly Telescope. The i' magnitudes of the quasars range from 18.03 to 20.68. Of the 99 new objects reported in this paper, 13 appear to be broad absorption line quasars. Five quasars, including one object at a redshift of 5.11, have 20 cm peak flux densities greater than 1 mJy. Two of the quasars, both at z ? 4.5, have very weak emission lines; one of these objects is a radio source. Nineteen of the newly discovered objects have redshifts above 4.6, and the maximum redshift is z = 5.41; among objects reported to date, the latter is the third highest redshift AGN and is penultimate in redshift among luminous quasars.

Weak‐Lensing Measurements of 42 SDSS/RASS Galaxy Clusters

We present a lensing study of 42 galaxy clusters imaged in Sloan Digital Sky Survey (SDSS) commissioning data. Cluster candidates are selected optically from SDSS imaging data and confirmed for this study by matching to X-ray sources found independently in the ROSAT All-Sky Survey (RASS). Five-color SDSS photometry is used to make accurate (Δz = 0.018) photometric redshift estimates that are used to rescale and combine the lensing measurements. The mean shear from these clusters is detected to 2 h-1 Mpc at the 7 σ level, corresponding to a mass within that radius of (4.2 ± 0.6) × 1014 h-1 M☉. The shear profile is well fitted by a power law with index -0.9 ± 0.3, consistent with that of an isothermal density profile. Clusters are divided by X-ray luminosity into two subsets, with mean LX of (0.14 ± 0.03) × 1044 and (1.0 ± 0.09) × 1044 h-2 ergs s-1. The average lensing signal is converted to a projected mass density based on fits to isothermal density profiles. From this we calculate a mean r500 (the radius at which the mean density falls to 500 times the critical density) and M(<r500). The mass contained within r500 differs substantially between the low- and high-LX bins, with (0.7 ± 0.2) × 1014 and 2.7×1014 h-1 M☉, respectively. This paper demonstrates our ability to measure ensemble cluster masses from SDSS imaging data. The full SDSS data set will include 1000 SDSS/RASS clusters. With this large data set we will measure the M-LX relation with high precision and put direct constraints on the mass density of the universe.

Optical and Infrared Colors of Stars Observed by the Two Micron All Sky Survey and the Sloan Digital Sky Survey

We discuss optical and infrared photometric properties of stars matched in the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) commissioning data for ~50 deg2 of sky along the celestial equator centered at l = 150°, b = -60°. About 98% (~63,000) of objects listed in the 2MASS Point Source Catalog in the analyzed area are matched within 2'' to an SDSS source. The matched sources represent 8% of the ~800,000 SDSS sources in this area. They are predominantly red sources, as expected, and 15% of them are resolved in SDSS imaging data although they are detected as point sources in 2MASS data. The distribution of positional discrepancies for the matched sources and the astrometric statistics for the multiply observed SDSS sources imply that the astrometric accuracy of both surveys is about 01 per coordinate (rms). For about 14,000 stars with the smallest photometric errors (10%) in both surveys, we present optical and infrared color-magnitude and color-color diagrams. We use optical (SDSS) colors to identify the stellar spectral sequence and show that stars of different spectral types can have similar infrared colors, thus making the classification of stars based on only 2MASS data very difficult. However, a broad separation into early and late spectral types (relative to type K0) is possible with a reliability of ~95% even with 2MASS colors alone. The distributions of matched sources in color-magnitude and color-color diagrams are compared with the predictions of a stellar population synthesis code. We find that the models are in fair overall agreement with the data. In particular, the total number counts agree to better than 10%, and the morphologies of the color-magnitude and color-color diagrams appear similar. The most significant discrepancies are found for the number ratio of early to late type stars (by about a factor of 2) and in the colors of M stars (up to 0.2 mag). The first disagreement indicates that some parameters of the standard Galactic structure model and/or initial mass function can be improved, and the second disagreement emphasizes known difficulties with the modeling of stellar atmospheres for cool stars.