Images of the CO 2-1 line emission, and the radio continuum emission, from
the redshift 4.12 gravitationally lensed quasi-stellar object (QSO) PSS
J2322+1944 reveal an Einstein ring with a diameter ...of 1.5". These observations
are modeled as a star forming disk surrounding the QSO nucleus with a radius of
2 kpc. The implied massive star formation rate is 900 M_sun/year. At this rate
a substantial fraction of the stars in a large elliptical galaxy could form on
a dynamical time scale of 10^8 years. The observation of active star formation
in the host galaxy of a high-redshift QSO supports the hypothesis of coeval
formation of supermassive black holes and stars in spheroidal galaxies.
Discovery of the cosmic reionization epoch would represent a significant milestone in cosmology. We present Keck spectroscopy of the quasar SDSS 1044-0125, at z = 5.73. The spectrum shows a dramatic ...increase in the optical depth at observed wavelengths lambda >~7550 A, corresponding to z_abs >~ 5.2. Only a few small, narrow transmission regions are present in the spectrum beyond that point, and out to the redshifts where the quasar signal begins. We interpret this result as a signature of the trailing edge of the cosmic reionization epoch, which we estimate to occur around ~ 6 (as indeed confirmed by subsequent observations by Becker et al.), and extending down to z \~ 5.2. This behavior is expected in the modern theoretical models of the reionization era, which predict a patchy and gradual onset of reionization. The remaining transmission windows we see may correspond to the individual reionization bubbles (Stromgren spheres) embedded in a still largely neutral intergalactic medium, intersected by the line of sight to the quasar. Future spectroscopic observations of quasars at comparable or larger redshifts will provide a more detailed insight into the structure and extent of the reionization era.
Astron.J.128:1017-1045, 2004 We present an optically selected galaxy cluster catalog from ~ 2,700 square
degrees of the Digitized Second Palomar Observatory Sky Survey (DPOSS),
spanning the redshift ...range 0.1 < z < 0.5, providing an intermediate redshift
supplement to the previous DPOSS cluster survey. This new catalog contains
9,956 cluster candidates and is the largest resource of rich clusters in this
redshift range to date. The candidates are detected using the best DPOSS plates
based on seeing and limiting magnitude. The search is further restricted to
high galactic latitude (|b| > 50), where stellar contamination is modest and
nearly uniform. We also present a performance comparison of two different
detection methods applied to this data, the Adaptive Kernel and Voronoi
Tessellation techniques. In the regime where both catalogs are expected to be
complete, we find excellent agreement, as well as with the most recent surveys
in the literature. Extensive simulations are performed and applied to the two
different methods, indicating a contamination rate of ~ 5%. These simulations
are also used to optimize the algorithms and evaluate the selection function
for the final cluster catalog. Redshift and richness estimates are also
provided, making possible the selection of subsamples for future studies.
Our current understanding of the low surface brightness universe is quite
incomplete, not only in the optical, but also in other wavelength regimes. As a
demonstration of the type of science which is ...facilitated by a virtual
observatory, we have undertaken a project utilizing both images and catalogs to
explore the multi-wavelength, low surface brightness universe. Here, we present
some initial results of this project. Our techniques are complimentary to
normal data reduction pipeline techniques in that we focus on the diffuse
emission that is ignored or removed by more traditional algorithms. This
requires a spatial filtering which must account for objects of interest, in
addition to observational artifacts (e.g., bright stellar halos). With this
work we are exploring the intersection of the catalog and image domains in
order to maximize the scientific information we can extract from the federation
of large survey data.
Like every other field of intellectual endeavor, astronomy is being
revolutionised by the advances in information technology. There is an ongoing
exponential growth in the volume, quality, and ...complexity of astronomical data
sets, mainly through large digital sky surveys and archives. The Virtual
Observatory (VO) concept represents a scientific and technological framework
needed to cope with this data flood. Systematic exploration of the observable
parameter spaces, covered by large digital sky surveys spanning a range of
wavelengths, will be one of the primary modes of research with a VO. This is
where the truly new discoveries will be made, and new insights be gained about
the already known astronomical objects and phenomena. We review some of the
methodological challenges posed by the analysis of large and complex data sets
expected in the VO-based research. The challenges are driven both by the size
and the complexity of the data sets (billions of data vectors in parameter
spaces of tens or hundreds of dimensions), by the heterogeneity of the data and
measurement errors, including differences in basic survey parameters for the
federated data sets (e.g., in the positional accuracy and resolution,
wavelength coverage, time baseline, etc.), various selection effects, as well
as the intrinsic clustering properties (functional form, topology) of the data
distributions in the parameter spaces of observed attributes. Answering these
challenges will require substantial collaborative efforts and partnerships
between astronomers, computer scientists, and statisticians.
We present a new, objectively defined catalog of candidate galaxy clusters
based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky
Survey (DPOSS). This cluster catalog, derived ...from the best calibrated plates
in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square
degrees, and contains 8,155 candidate clusters. A simple adaptive kernel
density mapping technique, combined with the SExtractor object detection
algorithm, is used to detect galaxy overdensities, which we identify as
clusters. Simulations of the background galaxy distribution and clusters of
varying richnesses and redshifts allow us to optimize detection parameters, and
measure the completeness and contamination rates for our catalog. Cluster
richnesses and photometric redshifts are measured, using integrated colors and
magnitudes for each cluster. An extensive spectroscopic survey is used to
confirm the photometric results.
This catalog, with well-characterized sample properties, provides a sound
basis for future studies of cluster physics and large scale structure.
Exploration of the time variability on the sky over a broad range of flux
levels and wavelengths is rapidly becoming a new frontier of astronomical
research. We describe here briefly the ...Palomar-QUEST survey being carried out
from the Samuel Oschin 48-inch Schmidt telescope at Palomar. The following
features make the survey an attractive candidate for studying time variability:
anticipated survey area of 12,000 - 15,000 sq. degrees in the drift scan mode,
point source depth of 21st mag. in I under good conditions, near simultaneous
observations in four filters, and at least four passes per year at each
location covered. The survey will yield a large number of transients and highly
variable sources in the near future and in that sense is a prototype of LSST
and Pan-STARRS. We briefly outline our strategy for searching such objects and
the proposed pipeline for detecting transients in real-time.
We present the photometric calibration technique for the Digitized Second
Palomar Observatory Sky Survey (DPOSS), used to create seamless catalogs of
calibrated objects over large sky areas. After ...applying a correction for
telescope vignetting, the extensive plate overlap regions are used to transform
sets of plates onto a common instrumental photometric system. Photometric
transformations to the Gunn gri system for each plate, for stars and galaxies,
are derived using these contiguous stitched areas and an extensive CCD imaging
library obtained for this purpose. We discuss the resulting photometric
accuracy, survey depth, and possible systematic errors.
We have identified eighty-four small, high density groups of galaxies out to z ~ 0.2 in a region of ~ 2000 square degrees around the north galactic pole using DPOSS (the Digitized Second Palomar ...Observatory Sky Survey). The groups have at least four galaxies satisfying more stringent criteria than those used by Hickson in his pioneering work in 1982: the adopted limiting surface brightness for each group is brighter (24 mag/arcsec^2 instead of 26 mag/arcsec^2), and the spread in magnitude among the member galaxies is narrower (two magnitudes instead of three). We also adopt a slightly modified version of the isolation criterion used by Hickson, in order to avoid rejecting groups with projected nearby faint background galaxies. A 10% contamination rate due to projection effects is expected for this sample based on extensive simulations.
We present a comparison of optical and X-ray properties of galaxy clusters in the northern sky. We determine the recovery rate of X-ray detected clusters in the optical as a function of richness, ...redshift and X-ray luminosity, showing that the missed clusters are typically low contrast systems when observed optically. We employ four different statistical tests to test for the presence of substructure using optical two-dimensional data, finding that approximately 35% of the clusters show strong signs of substructure. However, the results are test-dependent, with variations also due to the magnitude range and radius utilized.We have also performed a comparison of X-ray luminosity and temperature with optical galaxy counts (richness). We find that the slope and scatter of the relations between richness and the X-ray properties are heavily dependent on the density contrast of the clusters. The selection of substructure-free systems does not improve the correlation between X-ray luminosity and richness, but this comparison also shows much larger scatter than one obtained using the X-ray temperature. In the latter case, the sample is significantly reduced because temperature measurements are available only for the most massive (and thus high contrast) systems. However, the comparison between temperature and richness is very sensitive to the exclusion of clusters showing signs of substructure. The correlation of X-ray luminosity and richness is based on the largest sample to date (\(\sim\) 750 clusters), while tests involving temperature use a similar number of objects as previous works (\(\lsim\)100). The results presented here are in good agreement with existing literature.
