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Michael Berry,
Željko Ivezić,
Branimir Sesar,
Mario Jurić,
Edward F. Schlafly,
Jillian Bellovary, Douglas Finkbeiner,
Dijana Vrbanec,
Timothy C. Beers,
Keira J. Brooks, [......],
Brian Yanny,
Steven R. Majewski,
Gillian R. Knapp,
James E. Gunn,
J. Allyn Smith,
Masataka Fukugita,
Steve Kent,
John Barentine,
Jurek Krzesinski,
Dan Long
[show abstract]
[hide abstract]
ABSTRACT: We use SDSS photometry of 73 million stars to simultaneously obtain best-fit
main-sequence stellar energy distribution (SED) and amount of dust extinction
along the line of sight towards each star. Using a subsample of 23 million
stars with 2MASS photometry, whose addition enables more robust results, we
show that SDSS photometry alone is sufficient to break degeneracies between
intrinsic stellar color and dust amount when the shape of extinction curve is
fixed. When using both SDSS and 2MASS photometry, the ratio of the total to
selective absorption, $R_V$, can be determined with an uncertainty of about 0.1
for most stars in high-extinction regions. These fits enable detailed studies
of the dust properties and its spatial distribution, and of the stellar spatial
distribution at low Galactic latitudes. Our results are in good agreement with
the extinction normalization given by the Schlegel et al. (1998, SFD) dust maps
at high northern Galactic latitudes, but indicate that the SFD extinction map
appears to be consistently overestimated by about 20% in the southern sky, in
agreement with Schlafly et al. (2010). The constraints on the shape of the dust
extinction curve across the SDSS and 2MASS bandpasses support the models by
Fitzpatrick (1999) and Cardelli et al. (1989). For the latter, we find an
$R_V=3.0\pm0.1$(random) $\pm0.1$(systematic) over most of the high-latitude
sky. At low Galactic latitudes (|b|<5), we demonstrate that the SFD map cannot
be reliably used to correct for extinction as most stars are embedded in dust,
rather than behind it. We introduce a method for efficient selection of
candidate red giant stars in the disk, dubbed "dusty parallax relation", which
utilizes a correlation between distance and the extinction along the line of
sight. We make these best-fit parameters, as well as all the input SDSS and
2MASS data, publicly available in a user-friendly format.
11/2011;
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LSST Science Collaboration,
Paul A. Abell,
Julius Allison,
Scott F. Anderson,
John R. Andrew,
J. Roger P. Angel,
Lee Armus,
David Arnett,
S. J. Asztalos,
Tim S. Axelrod, [......],
Oliver Wiecha,
Benjamin F. Williams,
Beth Willman,
David Wittman,
Sidney C. Wolff,
W. Michael Wood-Vasey,
Przemek Wozniak,
Patrick Young,
Andrew Zentner,
Hu Zhan
[show abstract]
[hide abstract]
ABSTRACT: A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.
12/2009;
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Leonidas A. Moustakas,
Kevork Abazajian,
Andrew Benson,
Adam S. Bolton,
James S. Bullock,
Jacqueline Chen,
Edward Cheng,
Dan Coe,
Arthur B. Congdon,
Neal Dalal, [......],
Stefano Profumo,
Michael D. Seiffert,
Josh Simon,
Daniel Stern,
Louis Strigari,
James E. Taylor,
Randall Wayth,
Joachim Wambsganss,
Risa Wechsler,
Andrew Zentner
[show abstract]
[hide abstract]
ABSTRACT: There is a vast menagerie of plausible candidates for the constituents of dark matter, both within and beyond extensions of the Standard Model of particle physics. Each of these candidates may have scattering (and other) cross section properties that are consistent with the dark matter abundance, BBN, and the most scales in the matter power spectrum; but which may have vastly different behavior at sub-galactic "cutoff" scales, below which dark matter density fluctuations are smoothed out. The only way to quantitatively measure the power spectrum behavior at sub-galactic scales at distances beyond the local universe, and indeed over cosmic time, is through probes available in multiply imaged strong gravitational lenses. Gravitational potential perturbations by dark matter substructure encode information in the observed relative magnifications, positions, and time delays in a strong lens. Each of these is sensitive to a different moment of the substructure mass function and to different effective mass ranges of the substructure. The time delay perturbations, in particular, are proving to be largely immune to the degeneracies and systematic uncertainties that have impacted exploitation of strong lenses for such studies. There is great potential for a coordinated theoretical and observational effort to enable a sophisticated exploitation of strong gravitational lenses as direct probes of dark matter properties. This opportunity motivates this white paper, and drives the need for: a) strong support of the theoretical work necessary to understand all astrophysical consequences for different dark matter candidates; and b) tailored observational campaigns, and even a fully dedicated mission, to obtain the requisite data.
03/2009;
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Zeljko Ivezic,
Branimir Sesar,
Mario Juric,
Nicholas Bond,
Julianne Dalcanton,
Constance M. Rockosi,
Brian Yanny,
Heidi J. Newberg,
Timothy C. Beers,
Carlos Allende Prieto, [......],
Scott Kleinman,
Jurek Krzesinski,
Dan Long,
Atsuko Nitta,
Stephanie Snedden,
Brian Lee,
Hugh Harris,
Jonathan Brinkmann,
Donald P. Schneider,
Donald G. York
[show abstract]
[hide abstract]
ABSTRACT: Using effective temperature and metallicity derived from SDSS spectra for ~60,000 F and G type main sequence stars (0.2<g-r<0.6), we develop polynomial models for estimating these parameters from the SDSS u-g and g-r colors. We apply this method to SDSS photometric data for about 2 million F/G stars and measure the unbiased metallicity distribution for a complete volume-limited sample of stars at distances between 500 pc and 8 kpc. The metallicity distribution can be exquisitely modeled using two components with a spatially varying number ratio, that correspond to disk and halo. The two components also possess the kinematics expected for disk and halo stars. The metallicity of the halo component is spatially invariant, while the median disk metallicity smoothly decreases with distance from the Galactic plane from -0.6 at 500 pc to -0.8 beyond several kpc. The absence of a correlation between metallicity and kinematics for disk stars is in a conflict with the traditional decomposition in terms of thin and thick disks. We detect coherent substructures in the kinematics--metallicity space, such as the Monoceros stream, which rotates faster than the LSR, and has a median metallicity of [Fe/H]=-0.96, with an rms scatter of only ~0.15 dex. We extrapolate our results to the performance expected from the Large Synoptic Survey Telescope (LSST) and estimate that the LSST will obtain metallicity measurements accurate to 0.2 dex or better, with proper motion measurements accurate to ~0.2 mas/yr, for about 200 million F/G dwarf stars within a distance limit of ~100 kpc (g<23.5). [abridged]
05/2008;
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Željko Ivezić,
Kristen Menou,
Gillian R. Knapp,
Michael A. Strauss,
Robert H. Lupton,
Daniel E. Vanden Berk,
Gordon T. Richards,
Christy Tremonti,
Michael A. Weinstein,
Scott Anderson, [......],
Wolfgang Voges,
Richard L. White,
Brian Yanny,
Jonathan Brinkmann,
Mamoru Doi,
Masataka Fukugita,
Gregory S. Hennessy,
Jeffrey A. Munn,
Robert C. Nichol,
and Donald G. York
[show abstract]
[hide abstract]
ABSTRACT: We discuss the optical and radio properties of ~30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 15 with a Sloan Digital Sky Survey (SDSS) (optical, sensitive to r* ~ 22.2) source in 1230 deg2 of sky. The matched sample represents ~30% of the 108,000 FIRST sources and 0.1% of the 2.5 × 107 SDSS sources in the studied region. SDSS spectra are available for 4300 galaxies and 1154 quasars from the matched sample and for a control sample of 140,000 galaxies and 20,000 quasars in 1030 deg2 of sky. Here we analyze only core sources, which dominate the sample; the fraction of SDSS-FIRST sources with complex radio morphology is determined to be less than 10%. This large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r* = 21 are optically resolved; the fraction of resolved objects among the matched sources is a function of the radio flux, increasing from ~50% at the bright end to ~90% at the FIRST faint limit. Nearly all optically unresolved radio sources have nonstellar colors indicative of quasars. We estimate an upper limit of ~5% for the fraction of quasars with broadband optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux–optical flux plane suggests the existence of the "quasar radio dichotomy"; 8% ± 1% of all quasars with i* < 18.5 are radio-loud, and this fraction seems independent of redshift and optical luminosity. The radio-loud quasars have a redder median color by 0.08 ± 0.02 mag, and show a 3 times larger fraction of objects with extremely red colors. FIRST galaxies represent 5% of all SDSS galaxies with r* < 17.5, and 1% for r* < 20, and are dominated by red (u*-r* > 2.22) galaxies, especially those with r* > 17.5. Magnitude- and redshift-limited samples show that radio galaxies have a different optical luminosity distribution than nonradio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. For a given optical luminosity and redshift, the observed optical colors of radio galaxies are indistinguishable from those of all SDSS galaxies selected by identical criteria. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions and resulting selection effects are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. The fraction of radio galaxies whose emission-line ratios indicate an AGN (30%), rather than starburst, origin is 6 times larger than the corresponding fraction for all SDSS galaxies (r* < 17.5). We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies.
The Astronomical Journal 12/2007; 124(5):2364. · 4.03 Impact Factor
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Gordon T. Richards,
Xiaohui Fan,
Donald P. Schneider,
Daniel E. Vanden Berk,
Michael A. Strauss,
Donald G. York,
John E. Anderson,
Jr,
Scott F. Anderson,
James Annis, [......],
Chris Stoughton,
Christopher Stubbs,
Mark SubbaRao,
Alexander S. Szalay,
Gyula P. Szokoly,
Christy Tremonti,
Alan Uomoto,
Patrick Waddell,
Brian Yanny,
and Wei Zheng
[show abstract]
[hide abstract]
ABSTRACT: We present an empirical investigation of the colors of quasars in the Sloan Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625 quasars with SDSS photometry: 1759 quasars found during SDSS spectroscopic commissioning and SDSS follow-up observations on other telescopes, 50 matches to FIRST quasars, 573 matches to quasars from the NASA Extragalactic Database, and 243 quasars from two or more of these sources. The quasars are distributed in a 25 wide stripe centered on the celestial equator covering ~529 deg2. Positions (accurate to 02) and SDSS magnitudes are given for the 898 quasars known prior to SDSS spectroscopic commissioning. New SDSS quasars, which range in brightness from i* = 15.39 to the photometric magnitude limit of the survey, represent an increase of over 200% in the number of known quasars in this area of the sky. The ensemble average of the observed colors of quasars in the SDSS passbands are well represented by a power-law continuum with αν = -0.5 (fν ∝ να) and are close to those predicted by previous simulations. However, the contributions of the "small blue (or λ3000) bump" and other strong emission lines have a significant effect upon the colors. The color-redshift relation exhibits considerable structure, which may be of use in determining photometric redshifts for quasars from their colors alone. The range of colors at a given redshift can generally be accounted for by a range in the optical spectral index with a distribution αν = -0.5 ± 0.65 (95% confidence), but there is a red tail in the distribution. This tail may be a sign of internal reddening, especially since fainter objects at a given redshift tend to exhibit redder colors than the average. Finally, we show that there is a continuum of properties between quasars and Seyfert galaxies, and we test the validity of the traditional dividing line (MB = -23) between the two classes of active galactic nuclei.
The Astronomical Journal 12/2007; 121(5):2308. · 4.03 Impact Factor
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Daniel E. Vanden Berk,
Gordon T. Richards,
Amanda Bauer,
Michael A. Strauss,
Donald P. Schneider,
Timothy M. Heckman,
Donald G. York,
Patrick B. Hall,
Xiaohui Fan,
G. R. Knapp, [......],
Chris Stoughton,
Christopher Stubbs,
Mark SubbaRao,
Alexander S. Szalay,
Gyula P. Szokoly,
Christy Tremonti,
Alan Uomoto,
Patrick Waddell,
Brian Yanny,
and Wei Zheng
[show abstract]
[hide abstract]
ABSTRACT: We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 ≤ z ≤ 4.789 and an absolute r' magnitude range of -18.0 to -26.5. The input spectra cover an observed wavelength range of 3800–9200 Å at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 Å and reaches a peak signal-to-noise ratio of over 300 per 1 Å resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we find that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is 100 km s-1, compared with shifts of up to 550 km s-1 for some of the permitted and semiforbidden lines. At wavelengths longer than the Lyα emission, the continuum of the geometric mean composite is well fitted by two power laws, with a break at ≈5000 Å. The frequency power-law index, αν, is -0.44 from ≈1300 to 5000 Å and -2.45 redward of ≈5000 Å. The abrupt change in slope can be accounted for partly by host-galaxy contamination at low redshift. Stellar absorption lines, including higher order Balmer lines, seen in the composites suggest that young or intermediate-age stars make a significant contribution to the light of the host galaxies. Most of the spectrum is populated by blended emission lines, especially in the range 1500–3500 Å, which can make the estimation of quasar continua highly uncertain unless large ranges in wavelength are observed. An electronic table of the median quasar template is available.
The Astronomical Journal 12/2007; 122(2):549. · 4.03 Impact Factor
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Michael R. Blanton,
David J. Schlegel,
Michael A. Strauss,
J. Brinkmann, Douglas Finkbeiner,
Masataka Fukugita,
James E. Gunn,
David W. Hogg,
Željko Ivezić,
G. R. Knapp,
Robert H. Lupton,
Jeffrey A. Munn,
Donald P. Schneider,
Max Tegmark,
and Idit Zehavi
[show abstract]
[hide abstract]
ABSTRACT: Here we present the New York University Value-Added Galaxy Catalog (NYU-VAGC), a catalog of local galaxies (mostly below z ≈ 0.3) based on a set of publicly released surveys matched to the Sloan Digital Sky Survey (SDSS) Data Release 2. The photometric catalog consists of 693,319 galaxies, QSOs, and stars; 343,568 of these have redshift determinations, mostly from the SDSS. Excluding areas masked by bright stars, the photometric sample covers 3514 deg2, and the spectroscopic sample covers 2627 deg2 (with about 85% completeness). Earlier, proprietary versions of this catalog have formed the basis of many SDSS investigations of the power spectrum, correlation function, and luminosity function of galaxies. Future releases will follow future public releases of the SDSS. The catalog includes matches to the Two Micron All Sky Survey Point Source Catalog and Extended Source Catalog, the IRAS Point Source Catalog Redshift Survey, the Two-Degree Field Galaxy Redshift Survey, the Third Reference Catalogue of Bright Galaxies, and the Faint Images of the Radio Sky at Twenty cm survey. We calculate and compile derived quantities from the images and spectra of the galaxies in the catalogs (for example, K-corrections and structural parameters for the galaxies). The SDSS catalog presented here is photometrically calibrated in a more consistent way than that distributed by the SDSS Data Release 2 Archive Servers and is thus more appropriate for large-scale structure statistics, reducing systematic calibration errors across the sky from ~2% to ~1%. We include an explicit description of the geometry of the catalog, including all imaging and targeting information as a function of sky position. Finally, we have performed eyeball quality checks on a large number of objects in the catalog in order to flag errors (such as errors in deblending). This catalog is complementary to the SDSS Archive Servers in that NYU-VAGC's calibration, geometric description, and conveniently small size are specifically designed for studying galaxy properties and large-scale structure statistics using the SDSS spectroscopic catalog.
The Astronomical Journal 12/2007; 129(6):2562. · 4.03 Impact Factor
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Branimir Sesar,
Domjan Svilković,
Željko Ivezić,
Robert H. Lupton,
Jeffrey A. Munn, Douglas Finkbeiner,
William Steinhardt,
Rob Siverd,
David E. Johnston,
Gillian R. Knapp,
James E. Gunn,
Constance M. Rockosi,
David Schlegel,
Daniel E. Vanden Berk,
Pat Hall,
Donald P. Schneider,
and Robert J. Brunner
[show abstract]
[hide abstract]
ABSTRACT: We present a study of variable faint optical sources discovered by comparing the Sloan Digital Sky Survey (SDSS) and the Palomar Observatory Sky Survey (POSS) catalogs. We use SDSS measurements to photometrically recalibrate several publicly available POSS catalogs (USNO-A2.0, USNO-B1.0, DPOSS [the Digitized Second Palomar Observatory Sky Survey], and GSC2.2 [the Guide Star Catalog 2.2]). A piecewise recalibration of the POSS data in 100 arcmin2 patches (one SDSS field) generally results in an improvement of photometric accuracy (rms) by nearly a factor of 2, compared to the original data. In addition to the smaller core width of the error distribution, the tails of the distribution become much steeper after the recalibration. These improvements are mostly due to the very dense grid of calibration stars provided by SDSS, which rectifies the intrinsic inhomogeneities of Schmidt plates. We find that the POSS I magnitudes can be improved to ~0.15 mag accuracy, and POSS II magnitudes to ~0.10 mag accuracy. The smallest final errors are obtained with the GSC2.2 catalog, for which they approach 0.07 mag at the bright end. We use the recalibrated catalogs for the ~3300 deg2 of sky in the SDSS Data Release 2 to construct a catalog of ~60,000 sources that are variable on timescales of 10-50 yr, and make it publicly available. Using this catalog, we find that at least 1% of faint optical sources appear variable at the >0.25 mag level, and that about 20% of the variable population are quasars, although they represent only 0.6% of all point sources in the adopted flux-limited sample (g < 19). A series of statistical tests based on the morphology of SDSS color-magnitude and color-color diagrams, as well as visual comparison of images and comparison with repeated SDSS observations, demonstrate the robustness of the selection methods: three out of four candidate variable sources are correctly recognized to vary. We also demonstrate that candidate RR Lyrae stars trace the same halo structures, such as the Sgr dwarf tidal stream, that were discovered using repeated SDSS observations. We utilize the POSS-SDSS selected candidates to constrain the halo structure in the parts of sky for which repeated SDSS observations do not exist. We quantify the distribution of variable sources in the SDSS color-color diagrams and the variability characteristics of quasars. The observed long-term quasar variability (structure function) is smaller than predicted by the extrapolation of the power law measured for short timescales using repeated SDSS imaging (0.35 vs. 0.60 mag for SDSS-POSS I and 0.24 vs. 0.35 mag for SDSS-POSS II, rms). This turnover in structure function suggests that the characteristic timescale for quasar variability is on the order of 1 yr in the rest frame.
The Astronomical Journal 12/2007; 131(6):2801. · 4.03 Impact Factor
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Michael R. Blanton,
Julianne Dalcanton,
Daniel Eisenstein,
Jon Loveday,
Michael A. Strauss,
Mark SubbaRao,
David H. Weinberg,
John E. Anderson,
Jr,
James Annis, [......],
Aniruddha R. Thakar,
Christy Tremonti,
Douglas L. Tucker,
Alan Uomoto,
Dan Vanden Berk,
Michael S. Vogeley,
Patrick Waddell,
Brian Yanny,
Naoki Yasuda,
and Donald G. York
[show abstract]
[hide abstract]
ABSTRACT: In the course of its commissioning observations, the Sloan Digital Sky Survey (SDSS) has produced one of the largest redshift samples of galaxies selected from CCD images. Using 11,275 galaxies complete to r* = 17.6 over 140 deg2, we compute the luminosity function of galaxies in the r* band over a range -23 < M < -16 (for h = 1). The result is well-described by a Schechter function with parameters * = (1.46 ± 0.12) × 10-2 h3 Mpc-3, M* = -20.83 ± 0.03, and α = -1.20 ± 0.03. The implied luminosity density in r* is j ≈ (2.6 ± 0.3) × 108h L Mpc-3. We find that the surface brightness selection threshold has a negligible impact for M < -18. Using subsets of the data, we measure the luminosity function in the u*, g*, i*, and z* bands as well; the slope at low luminosities ranges from α = -1.35 to α = -1.2. We measure the bivariate distribution of r* luminosity with half-light surface brightness, intrinsic g*-r* color, and morphology. In agreement with previous studies, we find that high surface brightness, red, highly concentrated galaxies are on average more luminous than low surface brightness, blue, less concentrated galaxies. An important feature of the SDSS luminosity function is the use of Petrosian magnitudes, which measure a constant fraction of a galaxy's total light regardless of the amplitude of its surface brightness profile. If we synthesize results for RGKC band or bj band using these Petrosian magnitudes, we obtain luminosity densities 2 times that found by the Las Campanas Redshift Survey in RGKC and 1.4 times that found by the Two Degree Field Galaxy Redshift Survey in bj. However, we are able to reproduce the luminosity functions obtained by these surveys if we also mimic their isophotal limits for defining galaxy magnitudes, which are shallower and more redshift dependent than the Petrosian magnitudes used by the SDSS.
The Astronomical Journal 12/2007; 121(5):2358. · 4.03 Impact Factor
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Branimir Sesar,
Zeljko Ivezic,
Robert H. Lupton,
Mario Juric,
James E. Gunn,
Gillian R. Knapp,
Nathan De Lee,
J. Allyn Smith,
Gajus Miknaitis,
Huan Lin, [......],
Brian Lee,
Chris Stoughton,
Sebastian Jester,
Hugh Harris,
Paul Harding,
Jon Brinkmann,
Donald P. Schneider,
Donald York,
Michael W. Richmond,
Daniel Vanden Berk
[show abstract]
[hide abstract]
ABSTRACT: We quantify the variability of faint unresolved optical sources using a catalog based on multiple SDSS imaging observations. The catalog covers SDSS Stripe 82, and contains 58 million photometric observations in the SDSS ugriz system for 1.4 million unresolved sources. In each photometric bandpass we compute various low-order lightcurve statistics and use them to select and study variable sources. We find that 2% of unresolved optical sources brighter than g=20.5 appear variable at the 0.05 mag level (rms) simultaneously in the g and r bands. The majority (2/3) of these variable sources are low-redshift (<2) quasars, although they represent only 2% of all sources in the adopted flux-limited sample. We find that at least 90% of quasars are variable at the 0.03 mag level (rms) and confirm that variability is as good a method for finding low-redshift quasars as is the UV excess color selection (at high Galactic latitudes). We analyze the distribution of lightcurve skewness for quasars and find that is centered on zero. We find that about 1/4 of the variable stars are RR Lyrae stars, and that only 0.5% of stars from the main stellar locus are variable at the 0.05 mag level. The distribution of lightcurve skewness in the g-r vs. u-g color-color diagram on the main stellar locus is found to be bimodal (with one mode consistent with Algol-like behavior). Using over six hundred RR Lyrae stars, we demonstrate rich halo substructure out to distances of 100 kpc. We extrapolate these results to expected performance by the Large Synoptic Survey Telescope and estimate that it will obtain well-sampled 2% accurate, multi-color lightcurves for ~2 million low-redshift quasars, and will discover at least 50 million variable stars.
05/2007;
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Mario Juric,
Zeljko Ivezic,
Alyson Brooks,
Robert H. Lupton,
David Schlegel, Douglas Finkbeiner,
Nikhil Padmanabhan,
Nicholas Bond,
Branimir Sesar,
Constance M. Rockosi, [......],
J. Brinkmann,
Masataka Fukugita,
Michael Harvanek,
S. J. Kleinman,
Jurek Krzesinski,
Dan Long,
Neilsen, Jr., Eric H,
Atsuko Nitta,
Stephanie A. Snedden,
Donald G. York
[show abstract]
[hide abstract]
ABSTRACT: Abridged: We estimate the distances to ~48 million stars detected by the
Sloan Digital Sky Survey and map their 3D number density distribution in 100 <
D < 20 kpc range over 6,500 deg^2 of sky. The data show strong evidence for a
Galaxy consisting of an oblate halo, a disk component, and a number of
localized overdensities with exponential disk parameters (bias-corrected for an
assumed 35% binary fraction) H_1 = 300 pc, L_1 = 2600 pc, H_2 = 900 pc, L_2 =
3600 pc, and local density normalization of 12%. We find the halo to be oblate,
with best-fit axis ratio c/a = 0.64, r^{-2.8} profile, and the local
halo-to-thin disk normalization of 0.5%. We estimate the errors of derived
model parameters to be no larger than ~20% (disk scales) and ~10% (thick disk
normalization). While generally consistent with the above model, the density
distribution shows a number of statistically significant localized deviations.
We detect two overdensities in the thick disk region at (R, Z) ~ (6.5, 1.5)kpc
and (R, Z) ~ (9.5, 0.8) kpc, and a remarkable density enhancement in the halo
covering >1000deg^2 of sky towards the constellation of Virgo, at distances of
~6-20 kpc. Compared to a region symmetric with respect to the l=0 line, the
Virgo overdensity is responsible for a factor of 2 number density excess and
may be a nearby tidal stream or a low-surface brightness dwarf galaxy merging
with the Milky Way. After removal of the resolved overdensities, the remaining
data are consistent with a smooth density distribution; we detect no evidence
of further unresolved clumpy substructure at scales ranging from ~50pc in the
disk, to ~1 - 2 kpc in the halo.
11/2005;
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Michael R. Blanton,
David J. Schlegel,
Michael A. Strauss,
J. Brinkmann, Douglas Finkbeiner,
Masataka Fukugita,
James E. Gunn,
David W. Hogg,
Zeljko Ivezic,
G. R. Knapp,
Robert H. Lupton,
Jeffrey A. Munn,
Donald P. Schneider,
Max Tegmark,
Idit Zehavi
[show abstract]
[hide abstract]
ABSTRACT: Here we present the New York University Value-Added Galaxy Catalog (NYU-VAGC), a catalog of local galaxies (mostly below a redshift of about 0.3) based on a set of publicly-released surveys (including the 2dFGRS, 2MASS, PSCz, FIRST, and RC3) matched to the Sloan Digital Sky Survey (SDSS) Data Release 2. Excluding areas masked by bright stars, the photometric sample covers 3514 square degrees and the spectroscopic sample covers 2627 square degrees (with about 85% completeness). Earlier, proprietary versions of this catalog have formed the basis of many SDSS investigations of the power spectrum, correlation function, and luminosity function of galaxies. We calculate and compile derived quantities (for example, K-corrections and structural parameters for galaxies). The SDSS catalog presented here is photometrically recalibrated, reducing systematic calibration errors across the sky from about 2% to about 1%. We include an explicit description of the geometry of the catalog, including all imaging and targeting information as a function of sky position. Finally, we have performed eyeball quality checks on a large number of objects in the catalog in order to flag deblending and other errors. This catalog is complementary to the SDSS Archive Servers, in that NYU-VAGC's calibration, geometrical description, and conveniently small size are specifically designed for studying galaxy properties and large-scale structure statistics using the SDSS spectroscopic catalog. Comment: accepted by AJ; full resolution version available at http://sdss.physics.nyu.edu/vagc/va_paper.ps; data files available at http://sdss.physics.nyu.edu/vagc/
10/2004;
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Max Tegmark,
Michael A. Strauss,
Michael R. Blanton,
Kevork Abazajian,
Scott Dodelson,
Havard Sandvik,
Xiaomin Wang,
David H. Weinberg,
Idit Zehavi,
Neta A. Bahcall, [......],
John Peoples,
Jeffrey R. Pier,
Michael Richmond,
Constance Rockosi,
Donald P. Schneider,
Christopher Stoughton,
Douglas L. Tucker,
Daniel E. Vanden Berk,
Brian Yanny,
Donald G. York
[show abstract]
[hide abstract]
ABSTRACT: We measure cosmological parameters using the three-dimensional power spectrum 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 constant without tilt (ns=1), running tilt, tensor modes, or massive neutrinos. Adding SDSS information more than halves the WMAP-only error bars on some parameters, tightening 1σ constraints on the Hubble parameter from h≈0.74-0.07+0.18 to h≈0.70-0.03+0.04, on the matter density from Ωm≈0.25±0.10 to Ωm≈0.30±0.04 (1σ) and on neutrino masses from <11 to <0.6eV (95%). SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes and the equation of state. Our results are in substantial agreement with the joint analysis of WMAP and the Two Degree Field Galaxy Redshift Survey, which is an impressive consistency check with independent redshift survey data and analysis techniques. In this paper, we place particular emphasis on clarifying the physical origin of the constraints, i.e., what we do and do not know when using different data sets and prior assumptions. For instance, dropping the assumption that space is perfectly flat, the WMAP-only constraint on the measured age of the Universe tightens from t0≈16.3-1.8+2.3Gyr to t0≈14.1-0.9+1.0Gyr by adding SDSS and SN Ia data. Including tensors, running tilt, neutrino mass and equation of state in the list of free parameters, many constraints are still quite weak, but future cosmological measurements from SDSS and other sources should allow these to be substantially tightened.
Phys. Rev. D. 05/2004; 69(10).
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Andrew H. Jaffe,
Eric Gawiser, Douglas Finkbeiner,
Joanne C. Baker,
Amedeo Balbi,
Marc Davis,
Shaul Hanany,
William Holzapfel,
Mark Krumholz,
Leonidas Moustakas,
James Robinson,
Evan Scannapieco,
George F. Smoot,
Joseph Silk
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ABSTRACT: The Wavelength-Oriented Microwave Background Analysis Team (WOMBAT) is constructing microwave maps which will be more realistic than previous simulations. Our foreground models represent a considerable improvement: where spatial templates are available for a given foreground, we predict the flux and spectral index of that component at each place on the sky and estimate uncertainties. We will produce maps containing simulated CMB anisotropy combined with expected foregrounds. The simulated maps will be provided to the community as the WOMBAT Challenge, so such maps can be analyzed to extract cosmological parameters by scientists who are unaware of their input values. This will test the efficacy of foreground subtraction, power spectrum analysis, and parameter estimation techniques and help identify the areas most in need of progress. These maps are also part of the FORECAST project, which allows web-based access to the known foreground maps for the planning of CMB missions.
04/1999;
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Eric Gawiser, Douglas Finkbeiner,
Andrew Jaffe,
Joanne C. Baker,
Amedeo Balbi,
Marc Davis,
Shaul Hanany,
William Holzapfel,
Leonidas Moustakas,
James Robinson,
Evan Scannapieco,
George F. Smoot,
Joseph Silk
[show abstract]
[hide abstract]
ABSTRACT: The Wavelength-Oriented Microwave Background Analysis Team (WOMBAT) is constructing microwave skymaps which will be more realistic than previous simulations. Our foreground models represent a considerable improvement: where spatial templates are available for a given foreground, we predict the flux and spectral index of that component at each place on the sky and estimate the uncertainties in these quantities. We will produce maps containing simulated Cosmic Microwave Background anisotropies combined with all major expected foreground components. The simulated maps will be provided to the cosmology community as the WOMBAT Challenge, a "hounds and hares" exercise where such maps can be analyzed to extract cosmological parameters by scientists who are unaware of their input values. This exercise will test the efficacy of current foreground subtraction, power spectrum analysis, and parameter estimation techniques and will help identify the areas most in need of progress.
01/1999;
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Nicholas A. Bond,
Željko Ivezić,
Branimir Sesar,
Mario Jurić,
Jeffrey A. Munn,
Adam Kowalski,
Sarah Loebman,
Rok Roškar,
Timothy C. Beers,
Julianne Dalcanton, [......],
Scott Kleinman,
Jurek Krzesinski,
Dan Long,
Atsuko Nitta,
Stephanie Snedden,
Brian Lee,
Jeffrey R. Pier,
Hugh Harris,
Jonathan Brinkmann,
Donald P. Schneider
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ABSTRACT: We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r < 20 and proper-motion measurements derived from Sloan Digital Sky Survey (SDSS) and POSS astrometry, including ~170,000 stars with radial-velocity measurements from the SDSS spectroscopic survey. Distances to stars are determined using a photometric-parallax relation, covering a distance range from ~100 pc to 10 kpc over a quarter of the sky at high Galactic latitudes (|b|>20ð). We find that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (<100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.
The Astrophysical Journal, v.716, 1-29 (2010).
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Zeljko Ivezic,
J. Allyn Smith,
Gajus Miknaitis,
Huan Lin,
Douglas Tucker,
Robert H. Lupton,
James E. Gunn,
Gillian R. Knapp,
Michael A. Strauss,
Branimir Sesar, [......],
Nicholas Bond,
Brian Lee,
Chris Stoughton,
Sebastian Jester,
Hugh Harris,
Paul Harding,
Heather Morrison,
Jon Brinkmann,
Donald P. Schneider,
Donald York
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ABSTRACT: We describe a standard star catalog constructed using multiple SDSS photometric observations (at least four per band, with a median of 10) in the ugriz system. The catalog includes 1.01 million nonvariable unresolved objects from the equatorial stripe 82 (|deltaJ2000.0| < 1.266°) in the right ascension range 20h34m-4h00m and with the corresponding r-band (approximately Johnson V-band) magnitudes in the range 14-22. The distributions of measurements for individual sources demonstrate that the photometric pipeline correctly estimates random photometric errors, which are below 0.01 mag for stars brighter than 19.5, 20.5, 20.5, 20, and 18.5 in ugriz, respectively (about twice as good as for individual SDSS runs). Several independent tests of the internal consistency suggest that the spatial variation of photometric zero points is not larger than ~0.01 mag (rms). In addition to being the largest available data set with optical photometry internally consistent at the ~1% level, this catalog provides a practical definition of the SDSS photometric system. Using this catalog, we show that photometric zero points for SDSS observing runs can be calibrated within a nominal uncertainty of 2% even for data obtained through 1 mag thick clouds, and we demonstrate the existence of He and H white dwarf sequences using photometric data alone. Based on the properties of this catalog, we conclude that upcoming large-scale optical surveys such as the Large Synoptic Survey Telescope will be capable of delivering robust 1% photometry for billions of sources.
The Astronomical Journal, v.134, 973-998 (2007).
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Max Tegmark,
Michael R Blanton,
Michael A Strauss,
Fiona Hoyle,
David Schlegel,
Roman Scoccimarro,
Michael S Vogeley,
David H Weinberg,
Idit Zehavi,
Andreas Berlind, [......],
John Peoples,
Jeffrey R Pier,
Michael Richmond,
Constance Rockosi,
Donald P Schneider,
Christopher Stoughton,
Douglas L Tucker,
Daniel E Vanden,
Brian Yanny,
Donald G York
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ABSTRACT: We measure the large-scale real-space power spectrum PðkÞ by using a sample of 205,443 galaxies from the Sloan Digital Sky Survey, covering 2417 effective square degrees with mean redshift z % 0:1. We employ a matrix-based method using pseudo–Karhunen-Loève eigenmodes, producing uncorrelated minimum-variance measurements in 22 k-bands of both the clustering power and its anisotropy due to redshift-space distortions, with narrow and well-behaved window functions in the range 0:02 h Mpc À1 < k < 0:3 h Mpc À1 . We pay par-ticular attention to modeling, quantifying, and correcting for potential systematic errors, nonlinear redshift distortions, and the artificial red-tilt caused by luminosity-dependent bias. Our results are robust to omitting angular and radial density fluctuations and are consistent between different parts of the sky. Our final result is a measurement of the real-space matter power spectrum PðkÞ up to an unknown overall multiplicative bias factor. Our calculations suggest that this bias factor is independent of scale to better than a few percent for k < 0:1 h Mpc À1 , thereby making our results useful for precision measurements of cosmological parameters in conjunction with data from other experiments such as the Wilkinson Microwave Anisotropy Probe satellite. The power spectrum is not well-characterized by a single power law but unambiguously shows curvature. As a simple characterization of the data, our measurements are well fitted by a flat scale-invariant adiabatic cosmological model with h m ¼ 0:213 AE 0:023 and 8 ¼ 0:89 AE 0:02 for L Ã galaxies, when fixing the baryon fraction b = m ¼ 0:17 and the Hubble parameter h ¼ 0:72; cosmological interpretation is given in a companion paper.
