We present a model-independent, spherically symmetric density estimatorto be used in the cross-correlation of imaging catalogs with objects ofknown redshift. The estimator is a simple modification of the usualprojected density estimator, with weightings that produce a sphericalaperture rather than a cylindrical one.
Broadband measurements of flux for galaxies at different redshiftsmeasure different regions of the rest-frame galaxy spectrum. Certainastronomical questions, such as the evolution of the luminosity functionof galaxies, require transforming these inherently redshift-dependentmagnitudes into redshift-independent quantities. To prepare to addressthese astronomical questions, investigated in detail in subsequentpapers, we fit spectral energy distributions (SEDs) to broadbandphotometric observations in the context of the optical observations ofthe Sloan Digital Sky Survey (SDSS). Linear combinations of fourspectral templates can reproduce the five SDSS magnitudes of allgalaxies to the precision of the photometry. Expressed in theappropriate coordinate system, the locus of the coefficients multiplyingthe templates is planar and, in fact, nearly linear. The resultingreconstructed SEDs can be used to recover fixed-frame magnitudes over arange of redshifts. This process yields consistent results in the sensethat, within each sample, the intrinsic colors of similar type galaxiesare nearly constant with redshift. We compare our results with simplerinterpolation methods and galaxy spectrophotometry from the SDSS. Thesoftware that generates these results is publicly available and easilyadapted to handle a wide range of galaxy observations.Based on observations obtained with the Sloan Digital Sky Survey.
We present measurements of parameters of the three-dimensional powerspectrum of galaxy clustering from 222 square degrees of early imagingdata in the Sloan Digital Sky Survey (SDSS). The projected galaxydistribution on the sky is expanded over a set of Karhunen-Loève(KL) eigenfunctions, which optimize the signal-to-noise ratio in ouranalysis. A maximum likelihood analysis is used to estimate parametersthat set the shape and amplitude of the three-dimensional power spectrumof galaxies in the SDSS magnitude-limited sample withr*<21. Our best estimates are Γ=0.188+/-0.04 andσ8L=0.915+/-0.06 (statistical errors only), for a flatuniverse with a cosmological constant. We demonstrate that ourmeasurements contain signal from scales at or beyond the peak of thethree-dimensional power spectrum. We discuss how the results scale withsystematic uncertainties, like the radial selection function. We findthat the central values satisfy the analytically estimated scalingrelation. We have also explored the effects of evolutionary corrections,various truncations of the KL basis, seeing, sample size, and limitingmagnitude. We find that the impact of most of these uncertainties staywithin the 2 σ uncertainties of our fiducial result.
We report the discovery of a new gravitationally lensed quasar from theSloan Digital Sky Survey, SDSS J092455.87+021924.9 (SDSS J0924+0219).This object was selected from among known SDSS quasars by an algorithmthat was designed to select another known SDSS lensed quasar (SDSSJ1226-0006A,B). Five separate components, three of which are unresolved,are identified in photometric follow-up observations obtained with theMagellan Consortium's 6.5 m Walter Baade Telescope at Las CampanasObservatory. Two of the unresolved components (designated A and B) areconfirmed to be quasars with z=1.524; the velocity difference is lessthan 100 km s-1 according to spectra taken with the W. M.Keck Observatory's Keck II Telescope at Mauna Kea, Hawaii. A thirdstellar component, designated C, has the colors of a quasar withredshift similar to components A and B. The maximum separation of thepoint sources is 1.78". The other two sources, designated G and D, areresolved. Component G appears to be the best candidate for the lensinggalaxy. Although component D is near the expected position of the fourthlensed component in a four-image lens system, its properties are notconsistent with being the image of a quasar at z~1.5. Nevertheless, theidentical redshifts of components A and B and the presence of componentC strongly suggest that this object is a gravitational lens. Ourobservations support the idea that a foreground object reddens thefourth lensed component and that another unmodeled effect (such asmicro- or millilensing) demagnifies it, but we cannot rule out thepossibility that SDSS J0924+0219 is an example of the relatively rareclass of ``three-component'' lens systems.
We present early observations of the afterglow of GRB 030329 and thespectroscopic discovery of its associated supernova SN 2003dh. Weobtained spectra of the afterglow of GRB 030329 each night from March30.12 (0.6 days after the burst) to April 8.13 (UT) (9.6 days after theburst). The spectra cover a wavelength range of 350-850 nm. The earlyspectra consist of a power-law continuum(Fν~ν-0.9) with narrow emission linesoriginating from H II regions in the host galaxy, indicating a lowredshift of z=0.1687. However, our spectra taken after 2003 April 5 showbroad peaks in flux characteristic of a supernova. Correcting for theafterglow emission, we find that the spectrum of the supernova isremarkably similar to the Type Ic ``hypernova'' SN 1998bw. While thepresence of supernovae has been inferred from the light curves andcolors of gamma-ray burst afterglows in the past, this is the firstdirect, spectroscopic confirmation that a subset of classical gamma-raybursts originate from supernovae.Based on data from the Multiple Mirror Telescope Observatory 6.5 mtelescope, the Magellan 6.5 m Clay telescope, and the Fred LawrenceWhipple Observatory 1.5 m telescope.
An initial assessment is made of white dwarf and hot subdwarf starsobserved in the Sloan Digital Sky Survey. In a small area of sky (190square degrees), observed much like the full survey will be, 269 whitedwarfs (WDs) and 56 hot subdwarfs are identified spectroscopically whereonly 44 white dwarfs and five hot subdwarfs were known previously. Mostare ordinary DA (hydrogen atmosphere) and DB (helium) types. Inaddition, in the full survey to date, a number of WDs have been foundwith uncommon spectral types. Among these are blue DQ stars displayinglines of atomic carbon; red DQ stars showing molecular bands ofC2 with a wide variety of strengths; DZ stars where Ca andoccasionally Mg, Na, and/or Fe lines are detected; and magnetic WDs witha wide range of magnetic field strengths in DA, DB, DQ, and (probably)DZ spectral types. Photometry alone allows identification of starshotter than 12,000 K, and the density of these stars for 15-2 at Galactic latitudes of29°-62°. Spectra are obtained for roughly half of these hot
Using photometry and spectroscopy of 183,487 galaxies from the SloanDigital Sky Survey, we present bivariate distributions of pairs of sevengalaxy properties: four optical colors, surface brightness, radialprofile shape as measured by the Sérsic index, and absolutemagnitude. In addition, we present the dependence of local galaxydensity (smoothed on 8 h-1 Mpc scales) on all of theseproperties. Several classic, well-known relations among galaxyproperties are evident at extremely high signal-to-noise ratio: thecolor-color relations of galaxies, the color-magnitude relations, themagnitude-surface brightness relation, and the dependence of density oncolor and absolute magnitude. We show that most of the i-band luminositydensity in the universe is in the absolute magnitude and surfacebrightness ranges used: -23.50.1i<-17.0mag and 17<μ0.1i<24 mag in 1arcsec2 [the notation zb represents the b bandshifted blueward by a factor (1+z)]. Some of the relationships betweenparameters, in particular the color-magnitude relations, show strongercorrelations for exponential galaxies and concentrated galaxies takenseparately than for all galaxies taken together. We provide a simple setof fits of the dependence of galaxy properties on luminosity for thesetwo sets of galaxies and other quantitative details of our results.Based on observations obtained with the Sloan Digital Sky Survey.
The distribution of early-type galaxy velocity dispersions,φ(σ), is measured using a sample drawn from the Sloan DigitalSky Survey database. Its shape differs significantly from that obtainedby simply using the mean correlation between luminosity L and velocitydispersion σ to transform the luminosity function into a velocityfunction: ignoring the scatter around the mean σ-L relation is abad approximation. An estimate of the contribution from late-typegalaxies is also made, which suggests that φ(σ) is dominatedby early-type galaxies at velocities larger than ~200 km s-1.
Understanding the clustering of galaxies has long been a goal of modernobservational cosmology. Redshift surveys have been used to measure thecorrelation length as a function of luminosity and color. However, whensubdividing the catalogs into multiple subsets, the errors increaserapidly. Angular clustering in magnitude-limited photometric surveys hasthe advantage of much larger catalogs but suffers from a dilution of theclustering signal because of the broad radial distribution of thesample. Also, up to now it has not been possible to select uniformsubsamples based on physical parameters, such as luminosity andrest-frame color. Utilizing our photometric redshift technique, avolume-limited sample (0.10=5.77+/-0.10h-1Mpc. We find that r0increases with luminosity by a factor of 1.6 over the sampled luminosityrange, in agreement with previous redshift surveys. We also find thatboth the clustering length and the slope of the correlation functiondepend on the galaxy type. In particular, by splitting the galaxies infour groups by their rest-frame type, we find a bimodal behavior intheir clustering properties. Galaxies with spectral types similar toelliptical galaxies have a correlation length of6.59+/-0.17h-1Mpc and a slope of the angular correlationfunction of 0.96+/-0.05, while blue galaxies have a clustering length of4.51+/-0.19h-1Mpc and a slope of 0.68+/-0.09. The twointermediate color groups behave like their more extreme ``siblings''rather than showing a gradual transition in slope. We discuss thesecorrelations in the context of current cosmological models for structureformation.
The Sloan Digital Sky Survey (SDSS) has validated and made publiclyavailable its First Data Release. This consists of 2099 deg2of five-band (u,g,r,i,z) imaging data, 186,240 spectra of galaxies,quasars, stars and calibrating blank sky patches selected over 1360deg2 of this area, and tables of measured parameters fromthese data. The imaging data go to a depth of r~22.6 and are
Beyond its goals related to the extragalactic universe, the SloanDigital Sky Survey (SDSS) is an effective tool for identifying stellarobjects with unusual spectral energy distributions. Here we report onthe 53 new magnetic white dwarfs discovered during the first two yearsof the survey, including 38 whose data are made public in the 1500deg2 First Data Release. Discoveries span the magnitude range16.3<=g<=20.5, and based on the recovery rate for previously knownmagnetic white dwarfs, the completeness of the SDSS appears to be highfor reasonably hot stars with B>~3 MG and g>~15. The new objectsnearly double the total number of known magnetic white dwarfs andinclude examples with polar field strengths Bp>500 MG, aswell as several with exotic atmospheric compositions. The improvedsample statistics and uniformity indicate that the distribution ofmagnetic white dwarfs has a broad peak in the range ~5-30 MG and a tailextending to nearly 109 G. Degenerates with polar fieldsBp>~50 MG are consistent with being descendents ofmagnetic Ap/Bp main-sequence stars, but low- and moderate-field magneticwhite dwarfs appear to imply another origin. Yet-undetected magneticF-type stars with convective envelopes that destroy the orderedunderlying field are attractive candidates.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 report the discovery of a new gravitationally lensed quasar from theSloan Digital Sky Survey, SDSS J090334.92+502819.2. This object wastargeted for SDSS spectroscopy as a luminous red galaxy, but manualexamination of the spectrum showed the presence of a quasar at z~=3.6 inaddition to a red galaxy at z=0.388, and the SDSS image showed a secondpossible quasar image nearby. Follow-up imaging and spectroscopyconfirmed the lensing hypothesis. In images taken at the AstrophysicalResearch Consortium 3.5 m telescope, two quasars are separated by 2.8"the lensing galaxy is clearly seen and is blended with one of the quasarimages. Spectroscopy taken at the Keck II telescope shows that thequasars have identical redshifts of z~=3.6, and both show the presenceof the same broad absorption line-like troughs. We present simple lensmodels that account for the geometry and magnifications. The lens galaxylies near two groups of galaxies and may be a part of them. The modelssuggest that the groups may contribute considerable shear that has astrong effect on the lens configuration.
We discuss 18 white dwarfs, one of which (G227-5) was previously known,whose SDSS spectra show lines of neutral and/or singly ionized carbon.At least two and perhaps four show lines of neutral or singly ionizedoxygen. Apart from the extremely hot ``PG 1159'' stars, these are thefirst white dwarfs with photospheric oxygen detected in their opticalspectra. The photometry strongly suggests that these stars lie in the11,000-30,000 K temperature range of the helium-atmosphere DB whitedwarfs, though only one of them shows weak neutral helium lines in thespectrum. Trigonometric parallaxes are known for G227-5 and another,previously known white dwarf (G35-26) showing atomic carbon lines, andthey indicate that both are massive stars. Theoretical arguments suggestthat all members of this class of rare white dwarfs are massive (~1Msolar), and this finding could explain the paucity ofmassive DB white dwarfs.
We present the second edition of the Sloan Digital Sky Survey (SDSS)Quasar Catalog. The catalog consists of the 16,713 objects in the SDSSFirst 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, and have highly reliableredshifts. The area covered by the catalog is ~1360 deg2. Thequasar redshifts range from 0.08 to 5.41, with a median value of 1.43.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 some radio, near-infrared,and X-ray emission properties of the quasars, when available, from otherlarge-area surveys. Calibrated digital spectra of all objects in thecatalog, covering the wavelength region 3800-9200 Å at a spectralresolution of 1800-2100, are available. This publication supersedes thefirst SDSS Quasar Catalog, which was based on material from the SDSSEarly Data Release. A summary of corrections to current quasar databasesis also provided. The majority of the objects were found in SDSScommissioning data using a multicolor selection technique. Since thequasar selection algorithm was undergoing testing during the entireobservational period covered by this catalog, care must be taken whenassembling samples from the catalog for use in statistical studies. A
We show that the measurement of the baryonic acoustic oscillations inlarge high-redshift galaxy surveys offers a precision route to themeasurement of dark energy. The cosmic microwave background provides thescale of the oscillations as a standard ruler that can be measured inthe clustering of galaxies, thereby yielding the Hubble parameter andangular diameter distance as a function of redshift. This, in turn,enables one to probe dark energy. We use a Fisher matrix formalism tostudy the statistical errors for redshift surveys up to z=3 and reporterrors on cosmography while marginalizing over a large number ofcosmological parameters, including a time-dependent equation of state.With redshift surveys combined with cosmic microwave backgroundsatellite data, we achieve errors of 0.037 on ΩX, 0.10on w(z=0.8), and 0.28 on dw(z)/dz for the cosmological constant model.Models with less negative w(z) permit tighter constraints. We test anddiscuss the dependence of performance on redshift, survey conditions,and the fiducial model. We find results that are competitive with theperformance of future Type Ia supernova surveys. We conclude thatredshift surveys offer a promising independent route to the measurementof dark energy.
We present extensive optical and infrared photometry of the afterglow ofgamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dhover the first two months after detection (2003 March 30-May 29 UT).Optical spectroscopy from a variety of telescopes is shown and, whencombined with the photometry, allows an unambiguous separation betweenthe afterglow and SN contributions. The optical afterglow of the GRB isinitially a power-law continuum but shows significant color variationsduring the first week that are unrelated to the presence of an SN. Theearly afterglow light curve also shows deviations from the typicalpower-law decay. An SN spectrum is first detectable ~7 days after theburst and dominates the light after ~11 days. The spectral evolution andthe light curve are shown to closely resemble those of SN 1998bw, apeculiar Type Ic SN associated with GRB 980425, and the time of the SNexplosion is close to the observed time of the GRB. It is now clear thatat least some GRBs arise from core-collapse SNe.
Gravitational lensing is a powerful tool for the study of thedistribution of dark matter in the Universe. The cold-dark-matter modelof the formation of large-scale structures (that is, clusters ofgalaxies and even larger assemblies) predicts the existence of quasarsgravitationally lensed by concentrations of dark matter so massive thatthe quasar images would be split by over 7arcsec. Numerous searches forlarge-separation lensed quasars have, however, been unsuccessful. All ofthe roughly 70 lensed quasars known, including the first lensed quasardiscovered, have smaller separations that can be explained in terms ofgalaxy-scale concentrations of baryonic matter. Although gravitationallylensed galaxies with large separations are known, quasars are moreuseful cosmological probes because of the simplicity of the resultinglens systems. Here we report the discovery of a lensed quasar, SDSSJ1004 + 4112, which has a maximum separation between the components of14.62arcsec. Such a large separation means that the lensing object mustbe dominated by dark matter. Our results are fully consistent withtheoretical expectations based on the cold-dark-matter model.
The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopicsurvey that will eventually cover approximately one-quarter of thecelestial sphere and collect spectra of ~106 galaxies,100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001June, the SDSS released to the general astronomical community its earlydata release, roughly 462 deg2 of imaging data includingalmost 14 million detected objects and 54,008 follow-up spectra. Theimaging data were collected in drift-scan mode in five bandpasses (u, g,
We present initial results for counts in cell statistics of the angulardistribution of galaxies in early data from the Sloan Digital Sky Survey(SDSS). We analyze a rectangular stripe 2.5d wide, coveringapproximately 160 deg2, containing over 106galaxies in the apparent magnitude range 18'<22, withareas of bad seeing, contamination from bright stars, ghosts, and highgalactic extinction masked out. This survey region, which forms part ofthe SDSS early data release, is the same as that for which two-pointangular clustering statistics have recently been computed. The third andfourth moments of the cell counts, s3 (skewness) ands4 (kurtosis), constitute the most accurate measurements todate of these quantities (for r'<21) over angular scales0.015d-0.3d. They display the approximate hierarchical scaling expectedfrom nonlinear structure formation models and are in reasonableagreement with the predictions of Λ-dominated cold dark mattermodels with galaxy biasing that suppresses higher order correlations atsmall scales. The results are, in general, consistent with previousmeasurements in the APM, EDSGC, and Deeprange surveys. These resultssuggest that the SDSS imaging data are free of systematics to a highdegree and will therefore enable determination of the skewness and
We present the first measurements of clustering in the Sloan Digital SkySurvey (SDSS) galaxy redshift survey. Our sample consists of 29,300galaxies with redshifts5700kms-1<=cz<=39,000kms-1, distributed inseveral long but narrow (2.5d-5°) segments, covering 690deg2. For the full, flux-limited sample, the redshift-spacecorrelation length is approximately 8 h-1 Mpc. Thetwo-dimensional correlation function ξ(rp,π) showsclear signatures of both the small-scale, ``fingers-of-God'' distortioncaused by velocity dispersions in collapsed objects and the large-scalecompression caused by coherent flows, though the latter cannot bemeasured with high precision in the present sample. The inferredreal-space correlation function is well described by a power law,ξ(r)=(r/6.1+/-0.2h-1Mpc)-1.75+/-0.03, for0.1h-1Mpc<=r<=16h-1Mpc. The galaxy pairwisevelocity dispersion is σ12~600+/-100kms-1for projected separations0.15h-1Mpc<=rp<=5h-1Mpc. When wedivide the sample by color, the red galaxies exhibit a stronger andsteeper real-space correlation function and a higher pairwise velocitydispersion than do the blue galaxies. The relative behavior ofsubsamples defined by high/low profile concentration or high/low surfacebrightness is qualitatively similar to that of the red/blue subsamples.Our most striking result is a clear measurement of scale-independentluminosity bias at r<~10h-1Mpc: subsamples with absolutemagnitude ranges centered on M*-1.5, M*, andM*+1.5 have real-space correlation functions that areparallel power laws of slope ~-1.8 with correlation lengths ofapproximately 7.4, 6.3, and 4.7 h-1 Mpc, respectively.