Fifty-two magnetic white dwarfs have been identified in spectroscopicobservations from the Sloan Digital Sky Survey (SDSS) obtained betweenmid-2002 and the end of 2004, including Data Releases 2 and 3. Althoughnot as numerous or diverse as the discoveries from the first datarelease, the collection exhibits polar field strengths ranging from 1.5to ~1000 MG and includes two new unusual atomic DQA examples, amolecular DQ, and five stars that show hydrogen in fields above 500 MG.The highest field example, SDSS J2346+3853, may be the most stronglymagnetic white dwarf yet discovered. Analysis of the photometric dataindicates that the magnetic sample spans the same temperature range asfor nonmagnetic white dwarfs from the SDSS, and support is found forprevious claims that magnetic white dwarfs tend to have larger massesthan their nonmagnetic counterparts. A glaring exception to this trendis the apparently low-gravity object SDSS J0933+1022, which may have ahistory involving a close binary companion.A portion of the results presented here were obtained with the MMTObservatory, a facility operated jointly by the University of Arizonaand the Smithsonian Institution.

Mid-infrared photometry provides a robust technique for identifyingactive galaxies. While the ultraviolet to mid-infrared (λ<~5μm) continuum of stellar populations is dominated by the compositeblackbody curve and peaks at approximately 1.6 μm, the ultraviolet tomid-infrared continuum of active galactic nuclei (AGNs) is dominated bya power law. Consequently, with a sufficient wavelength baseline, onecan easily distinguish AGNs from stellar populations. Mirroring thetendency of AGNs to be bluer than galaxies in the ultraviolet, wheregalaxies (and stars) sample the blue, rising portion of stellar spectra,AGNs tend to be redder than galaxies in the mid-infrared, where galaxiessample the red, falling portion of the stellar spectra. We report onSpitzer Space Telescope mid-infrared colors, derived from the IRACShallow Survey, of nearly 10,000 spectroscopically identified sourcesfrom the AGN and Galaxy Evolution Survey. On the basis of thisspectroscopic sample, we find that simple mid-infrared color criteriaprovide remarkably robust separation of active galaxies from normal

This paper describes the observations and data reduction techniques forthe version 2.0 images and catalog of the Near-Infrared Camera andMulti-Object Spectrometer Ultra Deep Field (NICMOS UDF) Treasuryprogram. All sources discussed in this paper are based on detections inthe combined NICMOS F110W and F160W bands only. The NICMOS images aredrizzled to 0.09" pixel-1 and aligned to the Advanced Camerafor Surveys UDF F850LP image, which was rebinned to the same pixelscale. These form the NICMOS version 2.0 UDF images. The catalog sourcesare chosen with a conservative detection limit to avoid the inclusion ofnumerous spurious sources. The catalog contains 1293 objects in the144''×144'' NICMOS subfield of the UDF. The5 σ signal-to-noise ratio level is an average 0.6" diameteraperture AB magnitude of 27.7 at 1.1 and 1.6 μm. The catalog sources,listed in order of right ascension, satisfy a minimum signal-to-noiseratio criterion of 1.4 σ in at least seven contiguous pixels ofthe combined F110W and F160W image.

We examine the relationship between environment and the luminosities,surface brightnesses, colors, and profile shapes of luminous galaxies inthe Sloan Digital Sky Survey (SDSS). For the SDSS sample, galaxy coloris the galaxy property most predictive of the local environment. Galaxycolor and luminosity-measures of the star formation history-jointlycomprise the most predictive pair of properties. At fixed luminosity andcolor, density is not closely related to surface brightness or toSérsic index-measures of galaxy structure. In the text, wediscuss what measurable residual relationships exist, generally findingthat at red colors and fixed luminosity, the mean density decreases atthe highest surface brightnesses and Sérsic indices. In general,these results suggest that the structural properties of galaxies areless closely related to galaxy environment than are their masses andstar formation histories.Based on observations obtained with the Sloan Digital Sky Survey.

We report the discovery of a new two-image gravitationally lensedquasar, SDSS J024634.11-082536.2 (SDSS J0246-0825). This object wasselected as a lensed quasar candidate from the Sloan Digital Sky Survey(SDSS) by the same algorithm that was used to discover other SDSS lensedquasars (e.g., SDSS J0924+0219). Multicolor imaging with the MagellanConsortium's Walter Baade 6.5 m telescope and spectroscopic observationsusing the W. M. Keck Observatory's Keck II telescope confirm that SDSSJ0246-0825 consists of two lensed images (Δθ=1.04") of asource quasar at z=1.68. Imaging observations with the Keck I telescopeand the Hubble Space Telescope reveal an extended object between the twoquasar components, which is likely to be a lensing galaxy of thissystem. From the absorption lines in the spectra of the quasarcomponents and the apparent magnitude of the galaxy, combined with theexpected absolute magnitude from the Faber-Jackson relation, we estimatethe redshift of the lensing galaxy to be z=0.724. A highly distortedring is visible in the Hubble Space Telescope images, which is likely tobe the lensed host galaxy of the source quasar. Simple mass modelingpredicts the possibility that there is a small (faint) lensing objectnear the primary lensing galaxy.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS5-26555. These observations are associated withHST program 9744.

We present the third edition of the Sloan Digital Sky Survey (SDSS)Quasar Catalog. The catalog consists of the 46,420 objects in the SDSSThird Data Release that have luminosities larger than Mi=-22(in a cosmology with H0=70 km s-1Mpc-1, ΩM=0.3, andΩΛ=0.7), have at least one emission line withFWHM larger than 1000 km s-1 or are unambiguously broadabsorption line quasars, are fainter than i=15.0, and have highlyreliable redshifts. The area covered by the catalog is ~4188deg2. The quasar redshifts range from 0.08 to 5.41, with amedian value of 1.47; the high-redshift sample includes 520 quasars atredshifts greater than 4, of which 17 are at redshifts greater than 5.For each object the catalog presents positions accurate to better than0.2" rms per coordinate, five-band (ugriz) CCD-based photometry withtypical accuracy of 0.03 mag, and information on the morphology andselection method. The catalog also contains radio, near-infrared, andX-ray emission properties of the quasars, when available, from otherlarge-area surveys. The calibrated digital spectra cover the wavelengthregion 3800-9200 Å at a spectral resolution of ~=2000 the spectracan be retrieved from the public database using the information providedin the catalog. A total of 44,221 objects in the catalog were discoveredby the SDSS; 28,400 of the SDSS discoveries are reported here for thefirst time.

We construct and analyse a u-band selected galaxy sample from the SloanDigital Sky Survey (SDSS) Southern Survey, which covers275deg2. The sample includes 43223 galaxies withspectroscopic redshifts in the range 0.005 < z < 0.3 and with 14.5< u < 20.5. The signal-to-noise (S/N) ratio in the u-bandPetrosian aperture is improved by co-adding multiple epochs of imagingdata and by including sky-subtraction corrections. Luminosity functionsfor the near-UV 0.1u band (λ~ 322 +/- 26nm) aredetermined in redshift slices of width 0.02, which show a highlysignificant evolution in M* of -0.8 +/- 0.1 mag between z= 0 and 0.3;with M*-5 logh70=-18.84 +/- 0.05 (AB mag), logφ*=-2.06+/- 0.03 (h370Mpc-3) andlogρL= 19.11 +/- 0.02(h70WHz-1Mpc-3) at z= 0.1. Thefaint-end slope determined for z < 0.06 is given by α=-1.05 +/-0.08. This is in agreement with recent determinations from the GalaxyEvolution Explorer at shorter wavelengths. Comparing our z < 0.3luminosity density measurements with 0.2 < z < 1.2 fromClassifying Objects by Medium Band Observations in 17 Filters(COMBO-17), we find that the 280-nm density evolves asρL~ (1 +z)β with β= 2.1 +/- 0.2; andfind no evidence for any change in slope over this redshift range. Bycomparing with other measurements of cosmic star formation history, weestimate that the effective dust attenuation at 280nm has increased by0.8 +/- 0.3mag between z= 0 and 1.

We present the small-scale (0.2-7 h-1 Mpc) cross-correlationsbetween 32,000 luminous early-type galaxies and a reference sample of 16million normal galaxies from the Sloan Digital Sky Survey (SDSS). Ourmethod allows us to construct the spherically averaged, real-spacecross-correlation function between the spectroscopic luminous red galaxy(LRG) sample and galaxies from the SDSS imaging. We report thecross-correlation as a function of scale, luminosity, and redshift. Wefind very strong luminosity dependences in the clustering amplitudes, upto a factor of 4 over a factor of 4 in luminosity, and we measure thisdependence with a high signal-to-noise ratio. The luminosity dependenceof bias is found to depend on scale, with more variation on smallerscales. The clustering as a function of scale is not a power law butinstead has a dip at 1 h-1 Mpc and an excess on small scales.The fraction of red galaxies within the L* sample surroundingLRGs is a strong function of scale, as expected. However, the fractionof red galaxies evolves in redshift similarly on small and large scales,suggesting that cluster and field populations are changing in the samemanner. The results highlight the advantage on small scales of usingcross-correlation methods as a means of avoiding shot noise in samplesof rare galaxies.

This paper describes the Third Data Release of the Sloan Digital SkySurvey (SDSS). This release, containing data taken up through 2003 June,includes imaging data in five bands over 5282 deg2,photometric and astrometric catalogs of the 141 million objects detectedin these imaging data, and spectra of 528,640 objects selected over 4188deg2. The pipelines analyzing both images and spectroscopyare unchanged from those used in our Second Data Release.

We present the full spectroscopic white dwarf and hot subdwarf samplefrom the Sloan Digital Sky Survey (SDSS) first data release, DR1. Wefind 2551 white dwarf stars of various types, 240 hot subdwarf stars,and an additional 144 objects we have identified as uncertain whitedwarf stars. Of the white dwarf stars, 1888 are nonmagnetic DA types and171 are nonmagnetic DBs. The remaining (492) objects consist of alldifferent types of white dwarf stars: DO, DQ, DC, DH, DZ, hybrid starssuch as DAB, etc., and those with nondegenerate companions. We fit theDA and DB spectra with a grid of models to determine the Teffand logg for each object. For all objects, we provide coordinates,proper motions, SDSS photometric magnitudes, and enough information toretrieve the spectrum/image from the SDSS public database. This catalognearly doubles the known sample of spectroscopically identified whitedwarf stars. In the DR1 imaged area of the sky, we increase the knownsample of white dwarf stars by a factor of 8.5. We also comment onseveral particularly interesting objects in this sample.

We present estimates of cosmological parameters from the application ofthe Karhunen-Loève transform to the analysis of thethree-dimensional power spectrum of density fluctuations using SloanDigital Sky Survey galaxy redshifts. We use Ωmh andfb=Ωb/Ωm to describe theshape of the power spectrum, σL8g for the(linearly extrapolated) normalization, and β to parameterize lineartheory redshift-space distortions. On scales k<~0.16hMpc-1, our maximum likelihood values areΩmh=0.264+/-0.043, fb=0.286+/-0.065,σL8g=0.966+/-0.048, and β=0.45+/-0.12.When we take a prior on Ωb from the Wilkinson MicrowaveAnisotropy Probe (WMAP), we find Ωmh=0.207+/-0.030,which is in excellent agreement with WMAP and the Two-Degree Field. Thisindicates that we have reasonably measured the gross shape of the powerspectrum, but we have difficulty breaking the degeneracy betweenΩmh and fb, because the baryon oscillationsare not resolved in the current spectroscopic survey window function.

We measure cosmological parameters using the three-dimensional powerspectrum P(k) from over 200 000 galaxies in the Sloan Digital Sky Survey(SDSS) in combination with Wilkinson Microwave Anisotropy Probe (WMAP)and other data. Our results are consistent with a “vanilla”flat adiabatic cold dark matter model with a cosmological constantwithout tilt (ns=1), running tilt, tensor modes, or massiveneutrinos. Adding SDSS information more than halves the WMAP-only errorbars on some parameters, tightening 1σ constraints on the Hubbleparameter from h≈0.74+0.18-0.07 toh≈0.70+0.04-0.03, on the matter density fromΩm≈0.25±0.10 toΩm≈0.30±0.04 (1σ) and on neutrino

The distribution in color and absolute magnitude is presented for 55,158galaxies taken from the Sloan Digital Sky Survey in the redshift range0.08-1 Mpc and line-of-sighthalf-length 8 h-1 Mpc. In all environments, bulge-dominatedgalaxies (defined to be those with radial profiles best fitted withlarge Sérsic indices) have a color-magnitude diagram dominated byred galaxies for which the mode of the color distribution at fixedabsolute magnitude depends linearly on absolute magnitude. Although themost luminous galaxies reside preferentially in high-density regions andblue galaxies reside preferentially in low-density regions, there isonly a barely detectable variation with overdensity in the color (zeropoint) or slope of the linear relation between the mode color andluminosity [<0.02 mag in 0.1(g-r) or (B-V)]. These resultsconstrain variations with environmental density in the ages or

We have detected likely z~7-8 galaxies in the144''×144'' Near-Infrared Camera andMulti-Object Spectrometer (NICMOS) observations of the Hubble Ultra DeepField. Objects are required to be >=3 σ detections in bothNICMOS bands, J110 and H160. The selectioncriteria for this sample are(z850-J110)AB>0.8,(z850-J110)AB>0.66(J110-H160)AB+0.8,(J110-H160)AB<1.2 and no detectionat less than 8500 Å. The five selected sources have totalmagnitudes H160,AB~27. Four of the five sources are quiteblue compared to typical lower redshift dropout galaxies and areclustered within a 1 arcmin2 region. Because all five sourcesare near the limit of the NICMOS data, we have carefully evaluated theirreality. Each of the candidates is visible in different splits of thedata and a median stack. We analyzed several noise images and estimatethe number of spurious sources to be 1+/-1. A search using anindependent reduction of this same data set clearly revealed three ofthe five candidates and weakly detected a fourth candidate, suggestingthat the contamination could be higher. For comparison with predictionsfrom lower redshift samples, we take a conservative approach and adoptfour z~7-8 galaxies as our sample. With the same detection criteria onsimulated data sets, assuming no evolution from z~3.8, we predict 10sources at z~7-8, or 14 if we use a more realistic (1+z)-1size scaling. We estimate that the rest-frame continuum UV (~1800Å) luminosity density at z~7.5 (integrated down to0.3L*z=3) is just0.20+0.12-0.08 times that found at z~3.8 (or0.20+0.23-0.12 times this quantity includingcosmic variance). Effectively this sets an upper limit on the luminositydensity down to 0.3L*z=3 and is consistent withsignificant evolution at the bright end of the luminosity function fromz~7.5 to 3.8. Even with the lower UV luminosity density at z~7.5, itappears that galaxies could still play an important role in reionizationat these redshifts, although definitive measurements remain to be made.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555.

We analyze the spectrum of an unusually low mass white dwarf, SDSSJ123410.37-022802.9 (0335-264-52000), found in our recent, white dwarfcatalog from the first data release (DR1) of the Sloan Digital SkySurvey (SDSS). Two independent, model atmosphere fits result in anaccurate determination of atmospheric and stellar parameters. The morehands-on analysis yields Teff=17,470+/-750 K andlogg=6.38+/-0.05. We argue that the object cannot be a main-sequence Astar, a horizontal-branch star, or a subdwarf B star. Instead, it isinterpreted as a very low mass white dwarf with a core composed ofhelium, with mass ~0.18-0.19 Msolar, similar to thatpublished previously for the unusual companion to the millisecond pulsarJ1012+5307. The star probably remains in a binary, perhaps even with anundiscovered or dead pulsar companion. However, the companion might be amore ordinary star, provided Roche lobe mass transfer began shortlyafter the now-visible component left the main sequence. A second SDSSlow-mass white dwarf candidate is also analyzed, but the spectrum forthis fainter object is of poorer quality. The sample appears to includeadditional, similar candidates, worthy of more accurate observation.Correct identification of any additional white dwarfs of extremely lowmass requires careful observation and interpretation.

We study the recently discovered gravitational lens SDSS J1004+4112, thefirst quasar lensed by a cluster of galaxies. It consists of four imageswith a maximum separation of 14.62". The system was selected from thephotometric data of the Sloan Digital Sky Survey (SDSS) and has beenconfirmed as a lensed quasar at z=1.734 on the basis of deep imaging andspectroscopic follow-up observations. We present color-magnituderelations for galaxies near the lens plus spectroscopy of three centralcluster members, which unambiguously confirm that a cluster at z=0.68 isresponsible for the large image separation. We find a wide range of lensmodels consistent with the data, and despite considerable diversity theysuggest four general conclusions: (1) the brightest cluster galaxy andthe center of the cluster potential well appear to be offset by severalkiloparsecs; (2) the cluster mass distribution must be elongated in thenorth-south direction, which is consistent with the observeddistribution of cluster galaxies; (3) the inference of a large tidalshear (~0.2) suggests significant substructure in the cluster; and (4)enormous uncertainty in the predicted time delays between the imagesmeans that measuring the delays would greatly improve constraints on themodels. We also compute the probability of such large-separation lensingin the SDSS quasar sample on the basis of the cold dark matter model.The lack of large-separation lenses in previous surveys and thediscovery of one in SDSS together imply a mass fluctuation normalization

The z=3.02 quasar SDSS J095253.83+011421.9 exhibits broad metal-lineemission (C IV FWHM~=9000 km s-1), but broad Lyαemission is not present. Instead, only a narrow Lyα line isobserved (FWHM~=1140 km s-1). The large CIV/Lyα ratioin the broad-line region (BLR) emission from this object can be matchedmost closely by a BLR dominated by gas at very high densities(1015 cm-3), which suppresses the Lyαemission, and illuminated by an incident power law extending to ~200μm, which yields increased emission from purely collisionally excitedcoolant lines (such as C IV, N V, and O VI) but not from recombinationlines like Lyα. However, the strong C III emission predicted bythis model is not observed, and the observed broad C III] emission mustcome from a lower density BLR component and should be accompanied bybroad Lyα emission, which is not observed. The least unlikelyexplanation for this spectrum seems to be that any intrinsic broadLyα emission is removed by smooth N V absorption in the red wingof the Lyα emission line and by smooth Lyα absorption in theblue wing of the Lyα emission line. This postulated smoothabsorption would be in addition to the strong, associated, narrowabsorption seen in numerous ions. Smooth absorption in Lyα, N V,and O VI, but not in C IV, would be unusual, but not impossible,although it is suspicious that the postulated absorption must almostexactly cancel the postulated intrinsic broad emission. We conclude thatthe spectrum of SDSS J0952+0114 appears unique (among ~=3600 SDSSspectra of quasars at z>2.12) because of some combination of unusualparameters, and we discuss possible observations to determine thecombination of circumstances responsible for the spectrum.

We summarize the Sloan Digital Sky Survey data acquisition andprocessing steps, and describe runQA, a pipeline designed for automateddata quality assessment. In particular, we show how the position of thestellar locus in color-color diagrams can be used to estimate theaccuracy of photometric zeropoint calibration to better than 0.01 mag in0.03 deg2 patches. Using this method, we estimate thattypical photometric zeropoint calibration errors for SDSS imaging dataare not larger than ˜0.01 mag in the g, r, and i bands, 0.02 magin the z band, and 0.03 mag in the u band (root-mean-scatter forzeropoint offsets).

We report the discovery of SDSS J115517.35+634622.0, a previouslyunknown gravitationally lensed quasar. The lens system exhibits twoimages of a z=2.89 quasar, with an image separation of 1.832"+/-0.007".Near-IR imaging of the system reveals the presence of the lensing galaxybetween the two quasar images. Based on absorption features seen in theSloan Digital Sky Survey (SDSS) spectrum, we determine a lens galaxyredshift of z=0.1756. The lens is rather unusual in that one of thequasar images is only 0.22"+/-0.07" (~0.1 Reff) from thecenter of the lens galaxy, and photometric modeling indicates that thisimage is significantly brighter than predicted by a SIS model. Thissystem was discovered in the course of an ongoing search for stronglylensed quasars in the data set from the SDSS.

We report on the discovery of the two-image gravitationally lensedquasar SDSSJ1335 + 0118. The object was selected as a lens candidatefrom the Sloan Digital Sky Survey. The imaging and spectroscopicfollow-up observations confirm that the system exhibits twogravitationally lensed images of a quasar at z = 1.57. The imageseparation is 1''.56. We also detect an extended component between thetwo quasar images, likely to be a lensing galaxy. Preliminary massmodeling predicts a differential time delay, Δt of ˜30h-1 day, assuming the redshift of the lens galaxy to be 0.5.