We report on the discovery of a fifth lensed image in the largeseparation lensed quasar system SDSS J1004 + 4112. A faint point sourcelocated 0.''2 from the center of the brightest galaxy in the lensingcluster was detected in images taken with the Advanced Camera forSurveys (ACS) and the Near Infrared Camera and Multi-Object Spectrometer(NICMOS) on the Hubble Space Telescope. The flux ratio between the pointsource and the brightest lensed component in the ACS image is similar tothat in the NICMOS image. The location and brightness of the pointsource are consistent with lens model predictions for a lensed image. Wetherefore conclude that the point source is likely to be a fifth lensedimage of the source quasar. In addition, the NICMOS image reveals thelensed host galaxy of the source quasar, which can strongly constrainthe structure of the lensing critical curves, and thereby the massdistribution of the lensing cluster.

We report the discovery of 11 new variable DA white dwarf (ZZ Ceti)stars. Candidates were selected by deriving temperatures from model fitsto spectra obtained from the Sloan Digital Sky Survey (SDSS). We alsofind objects whose temperatures and gravities indicate they lie withinthe instability strip for pulsation but were not observed to vary.Although the temperatures are based on relatively low signal-to-noiseratio spectra, an impure strip is unexpected, which if confirmed, hasimplications for DA asteroseismology. This work brings the total numberof published variable DA white dwarf stars to 82.

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 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 M_i=-22(in a cosmology with H₀=70 km s^-1Mpc^-1, Ω_M=0.3, andΩ_Λ=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.

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.

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 study the relationship between galaxy luminosity, color, andenvironment in a cosmological simulation of galaxy formation. Using asimple prescription to assign colors and luminosities to simulatedgalaxies, we compare the predicted relationship with that observed forSDSS galaxies and find that the model successfully predicts most of thequalitative features seen in the data, but also shows some interestingdifferences. Specifically, the simulation predicts that the localdensity around bright red galaxies is a strong increasing function ofluminosity, but does not depend much on color at fixed luminosity.Moreover, we show that these trends are due to central galaxies in darkmatter halos whose baryonic masses correlate strongly with halo mass.The simulation also predicts that the local density around blue galaxiesis a strong increasing function of color, but does not depend much onluminosity at fixed color. We show that these trends are due tosatellite galaxies in halos whose stellar ages correlate with halo mass.Finally, the simulation fails to predict the luminosity dependence ofenvironments observed around low-luminosity red galaxies. However, weshow that this is most likely due to the simulation's limitedresolution. A study of a higher resolution, smaller volume simulationsuggests that this dependence is caused by the fact that alllow-luminosity red galaxies are satellites in massive halos, whereasintermediate-luminosity red galaxies are a mixture of satellites inmassive halos, and central galaxies in less massive halos.

A study has been made of the feasibility and scientific potential of a20-to 100-m aperture astronomical telescope at the lunar pole, with itsprimary mirror made of spinning liquid at < 100 K. Such a telescope,equipped with imaging and multiplexed spectroscopic instruments for adeep-infrared survey, would be revolutionary in its power to study thedistant Universe, including the formation of the first stars and theirassembly into galaxies. Our study explored the scientific opportunities,key technologies, and optimum location of such a Lunar Liquid MirrorTelescope (LLMT). An optical design for a 20- m telescope withdiffraction limited imaging over a 15-arcminute field has beendeveloped. It would be used to follow up on discoveries made with the6-m James Webb Space Telescope, with more detailed images andspectroscopic studies, as well as to detect objects 100 times fainter,such as the first high-redshift star in the early Universe. Amodel wasmade of a liquid mirror spinning on a superconducting bearing, as willbe needed for the cryogenic, vacuum environment of the LLMT. Reflectivesilver coatings have been deposited for the first time on a liquidsurface, needed to make infrared mirrors at ~80 K. Issues relating topolar locations have been explored. Dust on the optics or in a thinatmosphere, though unlikely to be problematic at the poles, should beinvestigated in-situ. Issues relating to polar locations have beenexplored. Locations at or within a few km of a pole are preferred fordeep-sky cover, and allow for long integration times by simpleinstrument rotation. This revolutionary mission concept could provide ascientific focus to NASA's planned exploration of the Moon, just ascurrently HST stands as a major achievement of its Shuttle Program.

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

We report the discovery of fourteen new ZZ Cetis with the 4.1 m SouthernAstrophysical Research telescope, at Cerro Pachon, in Chile. Thecandidates were selected from the SDSS (Sloan Digital Sky Survey) DAwhite dwarf stars with T_eff obtained from the optical spectrafit, inside the ZZ Ceti instability strip. Considering these stars aremulti-periodic pulsators and the pulsations propagate to the nucleus ofthe star, they carry information on the structure of the star andevolution of the progenitors. The ZZ Cetis discovered till 2003 aremainly within 100 pc from the Sun, and probe only the solar vicinity.The recently discovered ones, and those reported here, may sample adistinct population as they were selected mainly perpendicular to thegalactic disk and cover a distance up to ≈ 400 pc.

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 large-scale correlation function measured from aspectroscopic sample of 46,748 luminous red galaxies from the SloanDigital Sky Survey. The survey region covers 0.72 h^-3Gpc³ over 3816 deg² and 0.16-1 Mpcseparation that is an excellent match to the predicted shape andlocation of the imprint of the recombination-epoch acoustic oscillationson the low-redshift clustering of matter. This detection demonstratesthe linear growth of structure by gravitational instability betweenz~1000 and the present and confirms a firm prediction of the standardcosmological theory. The acoustic peak provides a standard ruler bywhich we can measure the ratio of the distances to z=0.35 and z=1089 to

Baryonic acoustic oscillations imprinted in the galaxy power spectrumprovide a promising tool for probing the cosmological distance scale anddark energy. We present results from a suite of cosmological N-bodysimulations aimed at investigating possible systematic errors in therecovery of cosmological distances. We show the robustness of baryonicpeaks against nonlinearity, redshift distortions, and mild biases withinthe linear and quasi-linear regime at various redshifts. While mildlybiased tracers follow the matter power spectrum well, redshiftdistortions do partially obscure baryonic features in redshift spacecompared to real space. We calculate the statistical constraints oncosmological distortions from N-body results and compare these to theanalytic results from a Fisher matrix formalism. We conclude that theangular diameter distance will be constrained as well as in our previousFisher matrix calculations while the Hubble parameter will be lessconstrained because of nonlinear redshift distortions.

I describe how acoustic oscillations imprinted into the late-timecorrelations of galaxies by baryonic physics at the epoch ofrecombination can be used as a cosmological standard ruler. Measurementsof this length scale by large galaxy surveys would allow us to computethe angular diameter distance to and Hubble parameter at the redshiftsof the survey. This in turn offers a robust way to measure theacceleration of the universe. I briefly present calculations of thestatistical performance from baseline surveys; full details of themethods and results are available in Seo and Eisenstein [ApJ, 598 (2003)720]. I discuss the advantages and disadvantages of the acousticoscillation method relative to other dark energy probes.

We analyse the flux power spectrum and its covariance using simulatedLyα forests. We find that pseudo-hydro techniques are goodapproximations of hydrodynamical simulations at high redshift. However,the pseudo-hydro techniques fail at low redshift because they areinsufficient for characterizing some components of the low-redshiftintergalactic medium, notably the warm-hot intergalactic medium. Hence,to use the low-redshift Lyα flux power spectrum to constraincosmology, one would need realistic hydrodynamical simulations. Bycomparing (one-dimensional) mass statistics with flux statistics, weshow that the non-linear transform between density and flux quenches thefluctuations so that the flux power spectrum is much less sensitive tocosmological parameters than the one-dimensional mass power spectrum.The covariance of the flux power spectrum is nearly Gaussian. As such,the uncertainties of the underlying mass power spectrum could still belarge, even though the flux power spectrum can be precisely determinedfrom a small number of lines of sight.

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

Two different simple measurements of galaxy star formation rate withdifferent timescales are compared empirically on 156,395 fiber spectraof galaxies with r<17.77 mag taken from the Sloan Digital Sky Surveyin the redshift range 0.05-4h³Mpc^-3Gyr^-1 atredshift z~0.1. These events are taking place in the field; the K+Agalaxies found in this study do not primarily lie in the high-densityenvironments or clusters typical of bulge-dominated populations.

Over the last few years, the Sloan Digital Sky Survey (SDSS) hasdiscovered several hundred quasars with redshift between 4.0 and 6.4.Including the effects of magnification bias, one expects a priori thatan appreciable fraction of these objects are gravitationally lensed. Wehave used the Advanced Camera for Surveys on the Hubble Space Telescopeto carry out a snapshot imaging survey of high-redshift SDSS quasars tosearch for gravitationally split lenses. This paper, the first in aseries reporting the results of the survey, describes snapshotobservations of four quasars at z=5.74, 5.82, 5.99, and 6.30,respectively. We find that none of these objects has a lensed companionwithin 5 mag with a separation larger than 0.3" within 2.5 mag we canrule out companions within 0.1". Based on the nondetection of stronglensing in these four systems, we constrain the z~6 luminosity functionto a slope of β>-4.63 (3 σ), assuming a break in thequasar luminosity function at M^*₁₄₅₀=-24.1. Wediscuss the implications of this constraint on the ionizing backgrounddue to quasars in the early universe. Given that these quasars are nothighly magnified, estimates of the masses of their central engines bythe Eddington argument must be taken seriously, possibly challengingmodels of black hole formation.

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 R_eff) 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 present a catalog of 49 spectroscopic strong gravitational lenscandidates selected from a Sloan Digital Sky Survey sample of 50,996luminous red galaxies. Potentially lensed star-forming galaxies aredetected through the presence of background oxygen and hydrogen nebularemission lines in the spectra of these massive foreground galaxies. Thismultiline selection eliminates the ambiguity of single-lineidentification and provides a very promising sample of candidategalaxy-galaxy lens systems at low to intermediate redshift, withforeground redshifts ranging from 0.16 to 0.49 and background redshiftsfrom 0.25 to 0.81. Any lenses confirmed within our sample would beimportant new probes of early-type galaxy mass distributions, providingcomplementary constraints to those obtained from currently known lensedhigh-redshift quasars.Based in part on observations obtained with the 6.5 m Clay telescope ofthe Magellan Consortium.