We describe the serendipitous discovery in the spectroscopic data of theSloan Digital Sky Survey of a starlike object, SDSS J103913.70+533029.7,at a heliocentric radial velocity of +1012 km s-1. Itsproximity in position and velocity to the spiral galaxy NGC 3310suggests an association with the galaxy. At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star cluster and aprojected distance of 17 kpc from NGC 3310. Its spectroscopic andphotometric properties imply a mass of >106Msolar and an age close to that of the tidal shells seenaround NGC 3310, suggesting that it formed in the event that formed theshells.
We present Sloan Digital Sky Survey (SDSS) photometry and spectroscopyin the fields of 27 gamma-ray bursts observed by Swift, including burstslocalized by Swift, HETE-2, and INTEGRAL, after 2004 December. Afterthis bulk release, we plan to provide individual releases of similardata shortly after the localization of future bursts falling in the SDSSsurvey area. These data provide a solid basis for the astrometric andphotometric calibration of follow-up afterglow searches and monitoring.Furthermore, the images provided with this release will allow observersto find transient objects up to a magnitude fainter than is possiblewith Digitized Sky Survey images.
We report on i-band snapshot observations of 157 Sloan Digital SkySurvey quasars at 4.0-3.8 (3 σ), assuming a break in the quasar luminosityfunction at M*1450~-24.5. This constraint isconsiderably stronger than the limit of β>-4.63 obtained fromthe absence of lensing in four z>5.7 quasars. Such constraints areimportant to our understanding of the true space density ofhigh-redshift quasars and the ionization state of the early universe.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555. These observations are associated with program9472.
In this paper we present the first results of a deep spectroscopicsurvey of faint quasars in the Sloan Digital Sky Survey (SDSS) SouthernSurvey, a deep survey carried out by repeatedly imaging a 270deg2 area. Quasar candidates were selected from the deep datawith good completeness over 02, contains 414 quasars, and
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 present the small-scale (0.01 Mpc-1 Mpc)projected correlation function wp(rp) andreal-space correlation function ξ(r) of 24,520 luminous early-typegalaxies from the Sloan Digital Sky Survey (SDSS) Luminous Red Galaxy(LRG) sample (0.16-2 power law over more than 4 orders of magnitudein separation r. This result is too steep at small scales to beexplained in current versions of the halo model for galaxy clustering.We infer an LRG-LRG merger rate of <~0.6×104Gyr-1 Gpc-3 for this sample. This result suggeststhat the LRG-LRG mergers are not the main mode of mass growth for LRGsat z<0.36.
A sample of white dwarfs is selected from the Sloan Digital Sky Survey(SDSS) Data Release 3 using their reduced proper motions, based onimproved proper motions from combined SDSS and USNO-B data. NumerousSDSS and follow-up spectra (Kilic and coworkers) are used to quantifycompleteness and contamination of the sample; kinematics models are usedto understand and correct for velocity-dependent selection biases. Aluminosity function is constructed covering the range7bol<16, and its sensitivity to various assumptionsand selection limits is discussed. The white dwarf luminosity functionbased on 6000 stars is remarkably smooth and rises nearly monotonicallyto Mbol=15.3. It then drops abruptly, although the smallnumber of low-luminosity stars in the sample and their unknownatmospheric composition prevent quantitative conclusions about thisdecline. Stars are identified that may have high tangential velocities,and a preliminary luminosity function is constructed for them.
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.
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 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 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.
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.
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.
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
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 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 Teff 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 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.
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 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.
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.