24 research outputs found
The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data
We report the discovery of a second field methane brown dwarf from the
commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS
J134646.45-003150.4 (SDSS 1346-00), was selected because of its very red color
and stellar appearance. Its spectrum between 0.8-2.5 mic is dominated by strong
absorption bands of H_2O and CH_4 and closely mimics those of Gliese 229B and
SDSS 162414.37+002915.6 (SDSS 1624+00), two other known methane brown dwarfs.
SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that
it lies about 11 pc from the sun. The ratio of flux at 2.1 mic to that at 1.27
mic is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which
suggests that SDSS 1346-00 has a slightly higher effective temperature than the
others. Based on a search area of 130 sq. deg. and a detection limit of z* =
19.8, we estimate a space density of 0.05 pc^-3 for methane brown dwarfs with
T_eff ~ 1000 K in the 40 pc^3 volume of our search. This estimate is based on
small-sample statistics and should be treated with appropriate caution.Comment: 9 pages, 3 figures, AASTeX, to appear in ApJ Letters, authors list
update
Five High-Redshift Quasars Discovered in Commissioning Imaging Data of the Sloan Digital Sky Survey
We report the discovery of five quasars with redshifts of 4.67 - 5.27 and
z'-band magnitudes of 19.5-20.7 M_B ~ -27. All were originally selected as
distant quasar candidates in optical/near-infrared photometry from the Sloan
Digital Sky Survey (SDSS), and most were confirmed as probable high-redshift
quasars by supplementing the SDSS data with J and K measurements. The quasars
possess strong, broad Lyman-alpha emission lines, with the characteristic sharp
cutoff on the blue side produced by Lyman-alpha forest absorption. Three
quasars contain strong, broad absorption features, and one of them exhibits
very strong N V emission. The amount of absorption produced by the Lyman-alpha
forest increases toward higher redshift, and that in the z=5.27 object (D_A ~
0.7) is consistent with a smooth extrapolation of the absorption seen in lower
redshift quasars. The high luminosity of these objects relative to most other
known objects at z >~ 5 makes them potentially valuable as probes of early
quasar properties and of the intervening intergalactic medium.Comment: 13 pages in LaTex format, two postscirpt figures. Submitted to the
Astronomical Journa
Evidence for Reionization at z ~ 6: Detection of a Gunn-Peterson Trough in a z=6.28 Quasar
We present moderate resolution Keck spectroscopy of quasars at z=5.82, 5.99
and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the
Ly Alpha absorption in the spectra of these quasars evolves strongly with
redshift. To z~5.7, the Ly Alpha absorption evolves as expected from an
extrapolation from lower redshifts. However, in the highest redshift object,
SDSSp J103027.10+052455.0 (z=6.28), the average transmitted flux is
0.0038+-0.0026 times that of the continuum level over 8450 A < lambda < 8710 A
(5.95<z(abs)<6.16), consistent with zero flux. Thus the flux level drops by a
factor of >150, and is consistent with zero flux in the Ly Alpha forest region
immediately blueward of the Ly Alpha emission line, compared with a drop by a
factor of ~10 at z(abs)~5.3. A similar break is seen at Ly Beta; because of the
decreased oscillator strength of this transition, this allows us to put a
considerably stronger limit, tau(eff) > 20, on the optical depth to Ly Alpha
absorption at z=6.
This is a clear detection of a complete Gunn-Peterson trough, caused by
neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen
fraction in the intergalactic medium would result in an undetectable flux in
the Ly Alpha forest region. Therefore, the existence of the Gunn-Peterson
trough by itself does not indicate that the quasar is observed prior to the
reionization epoch. However, the fast evolution of the mean absorption in these
high-redshift quasars suggests that the mean ionizing background along the line
of sight to this quasar has declined significantly from z~5 to 6, and the
universe is approaching the reionization epoch at z~6.Comment: Revised version (2001 Sep 4) accepted by the Astronomical Journal
(minor changes
Early-type galaxies in the SDSS. I. The sample
A sample of nearly 9000 early-type galaxies, in the redshift range 0.01 < z <
0.3, was selected from the Sloan Digital Sky Survey using morphological and
spectral criteria. This paper describes how the sample was selected, presents
examples of images and seeing corrected fits to the observed surface brightness
profiles, describes our method for estimating K-corrections, and shows that the
SDSS spectra are of sufficiently high quality to measure velocity dispersions
accurately. It also provides catalogs of the measured photometric and
spectroscopic parameters. In related papers, these data are used to study how
early-type galaxy observables, including luminosity, effective radius, surface
brightness, color, and velocity dispersion, are correlated with one another.Comment: 63 pages, 21 figures. Accepted by AJ (scheduled for April 2003). This
paper is part I of a revised version of astro-ph/0110344. The full version of
Tables 2 and 3, i.e. the tables listing the photometric and spectroscopic
parameters of ~ 9000 galaxies, are available at
http://astrophysics.phys.cmu.edu/~bernardi/SDSS/Etypes/TABLE
Detection of massive tidal tails around the globular cluster Pal 5 with SDSS commissioning data
We report the discovery of two well-defined tidal tails emerging from the
sparse remote globular cluster Palomar 5. These tails stretch out symmetrically
to both sides of the cluster in the direction of constant Galactic latitude and
subtend an angle of 2.6 degrees on the sky. The tails have been detected in
commissioning data of the Sloan Digital Sky Survey (SDSS), providing deep
five-color photometry in a 2.5 degrees wide band along the equator. The stars
in the tails make up a substantial part (~1/3) of the current total population
of cluster stars in the magnitude interval 19.5 < i* < 22.0. This reveals that
the cluster is subject to heavy mass loss. The orientation of the tails
provides an important key for the determination of the cluster's Galactic
orbit.Comment: 7 pages, 3 postscript figures, accepted for publication in ApJ
Letter
A Survey of z>5.8 Quasars in the Sloan Digital Sky Survey I: Discovery of Three New Quasars and the Spatial Density of Luminous Quasars at z~6
We present the results from a survey of i-dropout objects selected from ~1550
deg^2 of multicolor imaging data from the Sloan Digital Sky Survey, to search
for luminous quasars at z>5.8. Objects with i*-z*>2.2 and z*<20.2 are selected,
and follow-up J band photometry is used to separate L and T type cool dwarfs
from high-redshift quasars. We describe the discovery of three new quasars, at
z=5.82, 5.99 and 6.28, respectively. Their spectra show strong and broad Ly
alpha+NV emission lines, and very strong Ly alpha absorption, with a mean
continuum decrement D_A > 0.90. The ARC 3.5m spectrum of the z=6.28 quasar
shows that over a range of 300 A immediately blueward of the Ly alpha emission,
the average transmitted flux is only 0.003 +/-0.020 times that of the continuum
level, consistent with zero flux, and suggesting a tentative detection of the
complete Gunn-Peterson trough. The existence of strong metal lines suggests
early chemical enrichment in the quasar enviornment. The three new objects,
together with the previously published z=5.8 quasar form a complete
color-selected flux-limited sample at z>5.8. We estimate that at , the
comoving density of luminous quasars at M_1450 < -26.89 (h=0.5, Omega=1)is
1.1x10^-9 Mpc^-3. This is a factor of ~2 lower than that at z~5, and is
consistent with an extrapolation of the observed quasar evolution at low-z. We
discuss the contribution of quasars to the ionizing background at z~6. The
luminous quasars discussed in the paper have central black hole masses of
several times 10^9 M_sun by the Eddington argument. Their observed space
density provides a sensitive test of models of quasar and galaxy formation at
high redshift. (Abridged)Comment: AJ in press (Dec 2001), 40 pages, 10 figures. Updated following
referee report; minor change
Early-type galaxies in the SDSS. III. The Fundamental Plane
A magnitude limited sample of nearly 9000 early-type galaxies, in the
redshift range 0.01 < z < 0.3, was selected from the Sloan Digital Sky Survey
using morphological and spectral criteria. The Fundamental Plane relation in
this sample is R_o ~ sigma^{1.49\pm 0.05} I_o^{-0.75\pm 0.01} in the r* band.
It is approximately the same in the g*, i* and z* bands. Relative to the
population at the median redshift in the sample, galaxies at lower and higher
redshifts have evolved only little. If the Fundamental Plane is used to
quantify this evolution then the apparent magnitude limit can masquerade as
evolution; once this selection effect has been accounted for, the evolution is
consistent with that of a passively evolving population which formed the bulk
of its stars about 9 Gyrs ago. One of the principal advangtages of the SDSS
sample over previous samples is that the galaxies in it lie in environments
ranging from isolation in the field to the dense cores of clusters. The
Fundamental Plane shows that galaxies in dense regions are slightly different
from galaxies in less dense regions.Comment: 27 pages, 10 figures. Accepted by AJ (scheduled for April 2003). This
paper is part III of a revised version of astro-ph/011034
Early-type galaxies in the SDSS. IV. Colors and chemical evolution
The colors and chemical abundances of early-type galaxies at redshifts z<0.3
are studied using a sample of nearly 9000 galaxies, selected from the Sloan
Digital Sky Survey using morphological and spectral criteria. In this sample,
redder galaxies have larger velocity dispersions. Color also correlates with
magnitude and size, but these correlations are entirely due to the L-sigma and
R_o-sigma relations: the primary correlation is color-sigma. The red light in
early-type galaxies is, on average, slightly more centrally concentrated than
the blue. Because of these color gradients, the strength of the
color--magnitude relation depends on whether or not the colors are defined
using a fixed metric aperture. Chemical evolution and star formation histories
of early-type galaxies are investigated using co-added spectra of similar
objects. At fixed sigma, the population at z ~ 0.2 had weaker Mg_2 and stronger
H_beta absorption compared to the population at z ~ 0. It was also bluer.
Comparison of these colors and line-strengths, and their evolution, with
single-burst stellar population models suggests a formation time of 9 Gyrs ago,
consistent with a Fundamental Plane analysis of this sample.Comment: 38 pages, 16 figures. Accepted by AJ (scheduled for April 2003). This
paper is part IV of a revised version of astro-ph/0110344. The full version
of Table 3 and the 182 composite spectra can be downloaded from
http://astrophysics.phys.cmu.edu/~bernardi/SDSS/Etypes/SPECFITS A README file
(bernardi4.README) explains the content of the director
Cosmological parameters from SDSS and WMAP
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 WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (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 2dF 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+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr 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.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
The COMPARE Data Hubs
Data sharing enables research communities to exchange findings and build upon the knowledge that arises from their discoveries. Areas of public and animal health as well as food safety would benefit from rapid data sharing when it comes to emergencies. However, ethical, regulatory and institutional challenges, as well as lack of suitable platforms which provide an infrastructure for data sharing in structured formats, often lead to data not being shared or at most shared in form of supplementary materials in journal publications. Here, we describe an informatics platform that includes workflows for structured data storage, managing and pre-publication sharing of pathogen sequencing data and its analysis interpretations with relevant stakeholders