We present ugriz photometry and optical spectroscopy for 28 DB and DOwhite dwarfs with temperatures between 28,000 and 45,000 K. About 10 ofthese are particularly well observed; the remainder are candidates.These are the hottest DB stars yet found, and they populate the ``DBgap'' between the hotter DO stars and the familiar DB stars cooler than30,000 K. Nevertheless, after carefully matching the survey volumes wefind that the ratio of DA stars to DB stars is a factor of 2.5 larger at30,000 than at 20,000 K, suggesting that the ``DB gap'' is indeeddeficient and that some kind of atmospheric transformation takes place
We present the discovery of three z>5 quasars in the AGN and GalaxyEvolution Survey spectroscopic observations of the NOAO Deep Wide-FieldSurvey (NDWFS) Bootes Field. These quasars were selected as part of alarger Spitzer mid-infrared quasar sample, with no selection based onoptical colors. The highest redshift object, NDWFS J142516.3+325409, atz=5.85, is the lowest luminosity z>5.8 quasar currently known. Wecompare mid-infrared techniques for identifying z>5 quasars to moretraditional optical techniques and show that mid-infrared colors allowfor the selection of high-redshift quasars even at redshifts at whichquasars lie near the optical stellar locus and at z>7, where opticalselection is impossible. Using the superb multiwavelength coverageavailable in the NDWFS Bootes field, we construct the spectral energydistributions (SEDs) of high-redshift quasars from observedBW band to 24 μm (rest-frame 600 Å-3.7 μm). Weshow that the three high-redshift quasars have quite similar SEDs, andthe rest-frame composite SED of low-redshift quasars from the literatureshows little evolution compared to our high-redshift objects. We comparethe number of z>5 quasars we have discovered to the expected numberfrom published quasar luminosity functions. While analyses of the quasarluminosity function are tenuous based on only three objects, we findthat a relatively steep luminosity function with Ψ~L-3.2provides the best agreement with the number of high-redshift quasarsdiscovered in our survey.
We present results from Chandra observations of SDSS J1004+4112, astrongly lensed quasar system with a maximum image separation of 15".All four bright images of the quasar, as well as resolved X-ray emissionoriginating from the lensing cluster, are clearly detected. The emissionfrom the lensing cluster extends out to approximately 1.5 arcmin. Wemeasure the bolometric X-ray luminosity and temperature of the lensingcluster to be 4.7×1044 ergs s-1 and 6.4 keV,consistent with the luminosity-temperature relation for distantclusters. The mass estimated from the X-ray observation shows excellentagreement with the mass derived from gravitational lensing. The X-rayflux ratios of the quasar images differ markedly from the optical fluxratios, and the combined X-ray spectrum of the images possesses anunusually strong Fe Kα emission line, both of which are indicativeof microlensing.
We use the NICMOS Treasury and ACS HUDF images to measure theextinction-corrected star formation history for 4681 galaxies in theregion common to both images using the star formation rate distributionfunction and other techniques similar to those employed with the NICMOSand WFPC2 images in the HDFN. Unlike the HDFN, the NICMOS region of theHUDF appears to lack highly luminous and high star formation rategalaxies at redshifts beyond 3. The HUDF provides a region that iscompletely uncorrelated to the HDFN and therefore provides anindependent measure of the star formation history of the universe. Thecombined HUDF and HDFN star formation rates show an average rate of 0.2Msolar yr-1 Mpc-3. The average SFR ofthe combined fields at z=1-3 is 0.29 Msolar yr-1Mpc-3, while the average at z=4-6 is 1.2 Msolaryr-1 Mpc-3. The SFRs at all redshifts are within 3σ of the average over all redshifts.
We study the distribution of Eddington luminosity ratios,Lbol/LEdd, of active galactic nuclei (AGNs)discovered in the AGN and Galaxy Evolution Survey (AGES). We combineHβ, Mg II, and C IV line widths with continuum luminosities toestimate black hole (BH) masses in 407 AGNs, covering the redshift rangez~0.3-4 and the bolometric luminosity rangeLbol~1045-1047 ergs s-1. Thesample consists of X-ray or mid-infrared (24 μm) point sources withoptical magnitude R<=21.5 mag and optical emission-line spectracharacteristic of AGNs. For the range of luminosity and redshift probedby AGES, the distribution of estimated Eddington ratios is welldescribed as log-normal, with a peak atLbol/LEdd~=1/4 and a dispersion of 0.3 dex. Sinceadditional sources of scatter are minimal, this dispersion must accountfor contributions from the scatter between estimated and true BH massand the scatter between estimated and true bolometric luminosity.Therefore, we conclude that (1) neither of these sources of error cancontribute more than ~0.3 dex rms, and (2) the true Eddington ratios ofoptically luminous AGNs are even more sharply peaked. Because the massestimation errors must be smaller than ~0.3 dex, we can also investigatethe distribution of Eddington ratios at fixed BH mass. We show for thefirst time that the distribution of Eddington ratios at fixed BH mass ispeaked, and that the dearth of AGNs at a factor of ~10 below Eddingtonis real and not an artifact of sample selection. These results providestrong evidence that supermassive BHs gain most of their mass whileradiating close to the Eddington limit, and they suggest that thefueling rates in luminous AGNs are ultimately determined by BHself-regulation of the accretion flow rather than galactic-scaledynamical disturbances.Observations reported here were obtained at the MMT Observatory (MMTO),a joint facility of the University of Arizona and the SmithsonianInstitution.
We present the first data release of the Radial Velocity Experiment(RAVE), an ambitious spectroscopic survey to measure radial velocitiesand stellar atmosphere parameters (temperature, metallicity, and surfacegravity) of up to one million stars using the Six Degree Fieldmultiobject spectrograph on the 1.2 m UK Schmidt Telescope of theAnglo-Australian Observatory. The RAVE program started in 2003,obtaining medium-resolution spectra (median R=7500) in the Ca-tripletregion (8410-8795 Å) for southern hemisphere stars drawn from theTycho-2 and SuperCOSMOS catalogs, in the magnitude range 92. The average signal-to-noise ratio of
We present a spectroscopic survey of almost 15000 candidateintermediate-redshift luminous red galaxies (LRGs) brighter than i =19.8, observed with 2dF on the Anglo-Australian Telescope. The targetswere selected photometrically from the Sloan Digital Sky Survey (SDSS)and lie along two narrow equatorial strips covering 180 deg2.Reliable redshifts were obtained for 92 per cent of the targets and theselection is very efficient: over 90 per cent have 0.45 < z < 0.8.More than 80 per cent of the ~11000 red galaxies have pureabsorption-line spectra consistent with a passively evolving old stellarpopulation. The redshift, photometric and spatial distributions of theLRGs are described. The 2SLAQ data will be released publicly frommid-2006, providing a powerful resource for observational cosmology andthe study of galaxy evolution.
We present new measurements of the luminosity function (LF) of luminousred galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) and the 2dFSDSS LRG and Quasar (2SLAQ) survey. We have carefully quantified, andcorrected for, uncertainties in the K and evolutionary corrections,differences in the colour selection methods, and the effects ofphotometric errors, thus ensuring we are studying the same galaxypopulation in both surveys. Using a limited subset of 6326 SDSS LRGs(with 0.17 < z < 0.24) and 1725 2SLAQ LRGs (with 0.5 < z <0.6), for which the matching colour selection is most reliable, we findno evidence for any additional evolution in the LRG LF, over thisredshift range, beyond that expected from a simple passive evolutionmodel. This lack of additional evolution is quantified using thecomoving luminosity density of SDSS and 2SLAQ LRGs, brighter thanM0.2r - 5 log h0.7 = -22.5, which are2.51 +/- 0.03 × 10-7LsolarMpc-3and 2.44 +/- 0.15 ×10-7LsolarMpc-3, respectively (<10per cent uncertainty). We compare our LFs to the COMBO-17 data and findexcellent agreement over the same redshift range. Together, thesesurveys show no evidence for additional evolution (beyond passive) inthe LF of LRGs brighter than M0.2r - 5 logh0.7 = -21 (or brighter than ~L*). We test our SDSS and 2SLAQLFs against a simple `dry merger' model for the evolution of massive redgalaxies and find that at least half of the LRGs at z ~= 0.2 mustalready have been well assembled (with more than half their stellarmass) by z ~= 0.6. This limit is barely consistent with recent resultsfrom semi-analytical models of galaxy evolution.
Accurate photometric redshifts are calculated for nearly 200,000galaxies to a 4.5 μm flux limit of ~13 μJy in the 8.5deg2 Spitzer IRAC Shallow Survey. Using a hybrid photometricredshift algorithm incorporating both neural net and template-fittingtechniques, calibrated with over 15,000 spectroscopic redshifts, a
We present a catalog of 9316 spectroscopically confirmed white dwarfsfrom the Sloan Digital Sky Survey Data Release 4. We have selected thestars through photometric cuts and spectroscopic modeling, backed up bya set of visual inspections. About 6000 of the stars are newdiscoveries, roughly doubling the number of spectroscopically confirmedwhite dwarfs. We analyze the stars by performing temperature and surfacegravity fits to grids of pure hydrogen and helium atmospheres. Among therare outliers are a set of presumed helium-core DA white dwarfs withestimated masses below 0.3 Msolar, including two candidatesthat may be the lowest-mass yet found. We also present a list of 928 hotsubdwarfs.
We present a detailed investigation into the recent star formationhistories of 5697 luminous red galaxies (LRGs) based on the Hδ(4101 Å), and [OII] (3727 Å) lines and the D4000 index. LRGsare luminous (L > 3L*) galaxies which have been selected to havephotometric properties consistent with an old, passively evolvingstellar population. For this study, we utilize LRGs from the recentlycompleted 2dF-SDSS LRG and QSO Survey (2SLAQ). Equivalent widths of theHδ and [OII] lines are measured and used to define three spectraltypes, those with only strong Hδ absorption (k+a), those withstrong [OII] in emission (em) and those with both (em+a). All other LRGsare considered to have passive star formation histories. The vastmajority of LRGs are found to be passive (~80 per cent); however,significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and emLRGs (8.6 per cent) are identified. An investigation into the redshiftdependence of the fractions is also performed. A sample of SDSS MAINgalaxies with colours and luminosities consistent with the 2SLAQ LRGs isselected to provide a low-redshift comparison. While the em and em+afractions are consistent with the low-redshift SDSS sample, the fractionof k+a LRGs is found to increase significantly with redshift. Thisresult is interpreted as an indication of an increasing amount of recentstar formation activity in LRGs with redshift. By considering theexpected lifetime of the k+a phase, the number of LRGs which willundergo a k+a phase can be estimated. A crude comparison of thisestimate with the predictions from semi-analytic models of galaxyformation shows that the predicted level of k+a and em+a activities isnot sufficient to reconcile the predicted mass growth for massive earlytypes in a hierarchical merging scenario.
We measure the large-scale real-space power spectrum P(k) using luminousred galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS) and use thismeasurement to sharpen constraints on cosmological parameters from theWilkinson Microwave Anisotropy Probe (WMAP). We employ a matrix-basedpower spectrum estimation method using Pseudo-Karhunen-Loèveeigenmodes, producing uncorrelated minimum-variance measurements in 20k-bands of both the clustering power and its anisotropy due toredshift-space distortions, with narrow and well-behaved windowfunctions in the range 0.01h/Mpcm and the baryon fraction in goodagreement with WMAP. Within the context of flat ΛCDM models, ourLRG measurements complement WMAP by sharpening the constraints on thematter density, the neutrino density and the tensor amplitude by about afactor of 2, giving Ωm=0.24±0.02 (1σ),
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 report the intermediate-scale (0.3-40 h-1 Mpc) clusteringof 35,000 luminous early-type galaxies at redshifts 0.16-0.44 from theSloan Digital Sky Survey. We present the redshift space two-pointcorrelation function ξ(s), the projected correlation functionwp(rp), and the deprojected real space correlationfunction ξ(r), for approximately volume-limited samples. As expected,the galaxies are highly clustered, with the correlation length varyingfrom 9.8+/-0.2 to 11.2 +/- 0.2 h-1 Mpc, dependent on thespecific luminosity range. For the -23.2g<-21.2sample, the inferred bias relative to that of L* galaxies is1.84+/-0.11 for1h-1Mpcp<~10h-1Mpc, with yetstronger clustering on smaller scales. We detect luminosity-dependentbias within the sample but see no evidence for redshift evolutionbetween z=0.2 and z=0.4. We find a clear indication for deviations froma power-law in the real space correlation function, with a dip at ~2h-1 Mpc scales and an upturn on smaller scales. The precisionmeasurements of these clustering trends offer new avenues for the studyof the formation and evolution of these massive galaxies.
We analyse the covariance of the one-dimensional mass power spectrumalong lines of sight. The covariance reveals the correlation betweendifferent modes of fluctuations in the cosmic density field and givesthe sample variance error for measurements of the mass power spectrum.For Gaussian random fields, the covariance matrix is diagonal. Asexpected, the variance of the measured one-dimensional mass powerspectrum is inversely proportional to the number of lines of sight thatare sampled from each random field. The correlation between lines ofsight in a single field may alter the covariance. However, lines ofsight that are sampled far apart are only weakly correlated, so thatthey can be treated as independent samples. Using N-body simulations, wefind that the covariance matrix of the one-dimensional mass powerspectrum is not diagonal for the cosmic density field due to thenon-Gaussianity and that the variance is much higher than that ofGaussian random fields. From the covariance, one will be able todetermine the cosmic variance in the measured one-dimensional mass powerspectrum as well as to estimate how many lines of sight are needed toachieve a target precision.
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 test the homogeneity of the universe at z~0.3 with the luminous redgalaxy (LRG) spectroscopic sample of the Sloan Digital Sky Survey.First, the mean number N(R) of LRGs within completely surveyedLRG-centered spheres of comoving radius R is shown to be proportional toR3 at radii greater than R~70h-1Mpc. The test hasthe virtue that it does not rely on the assumption that the LRG samplehas a finite mean density; its results show, however, that there is sucha mean density. Second, the survey sky area is divided into 10 disjointsolid angular regions, and the fractional rms density variations of theLRG sample in the redshift range 0.27h-3Mpc3) regions is found
We discuss the construction of a photometric redshift catalogue ofluminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS),emphasizing the principal steps necessary for constructing such acatalogue: (i) photometrically selecting the sample, (ii) measuringphotometric redshifts and their error distributions, and (iii)estimating the true redshift distribution. We compare two photometricredshift algorithms for these data and find that they give comparableresults. Calibrating against the SDSS and SDSS-2dF (Two Degree Field)spectroscopic surveys, we find that the photometric redshift accuracy isσ~ 0.03 for redshifts less than 0.55 and worsens at higherredshift (~0.06 for z < 0.7). These errors are caused by photometricscatter, as well as systematic errors in the templates, filter curvesand photometric zero-points. We also parametrize the photometricredshift error distribution with a sum of Gaussians and use this modelto deconvolve the errors from the measured photometric redshiftdistribution to estimate the true redshift distribution. We pay specialattention to the stability of this deconvolution, regularizing themethod with a prior on the smoothness of the true redshift distribution.The methods that we develop are applicable to general photometricredshift surveys.
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.