428 research outputs found
Multi-object spectroscopy of low redshift EIS clusters. I
We report the results of the first multi-object spectroscopic observations at
the Danish 1.54m telescope at La Silla, Chile. Observations of five cluster
candidates from the ESO Imaging Survey Cluster Candidate Catalog are described.
From these observations we confirm the reality of the five clusters with
measured redshifts of 0.11<=z<=0.35. We estimate velocity dispersions in the
range 294-621km/s indicating rather poor clusters. This, and the measured
cluster redshifts are consistent with the results of the matched filter
procedure applied to produce the Cluster Candidate Catalog.Comment: 7pages, accepted by Astronomy and Astrophysic
Regularity bounds by minimal generators and Hilbert function
Let be the regularity of the Hilbert function of a projective curve in \mbox {P}^n_K over an algebraically closed field and
be degrees for which there exists a complete intersection of type () containing properly . Then the Castelnuovo-Mumford regularity of is bounded above by max .We investigate the sharpness of the above bound, which is achieved by curves algebraically linked to ones having degenerate general hyperplane section
A global radiosonde and tracked balloon archive on 16 pressure levels (GRASP) back to 1905 – Part 1: Merging and interpolation to 00:00 and 12:00 GMT
Many observed time series of the global
radiosonde or PILOT networks exist as fragments distributed over different
archives. Identifying and merging these fragments can enhance their value for
studies on the three-dimensional spatial structure of climate change.
<br><br>
The Comprehensive Historical Upper-Air Network (CHUAN version 1.7), which was substantially extended in 2013,
and the Integrated Global Radiosonde
Archive (IGRA) are the most important collections of upper-air measurements
taken before 1958. CHUAN (tracked) balloon data start in 1900, with higher
numbers from the late 1920s onward, whereas IGRA data start in 1937. However,
a substantial fraction of those measurements have not been taken at synoptic
times (preferably 00:00 or 12:00 GMT) and on altitude levels instead of standard
pressure levels. To make them comparable with more recent data, the records
have been brought to synoptic times and standard pressure levels using
state-of-the-art interpolation techniques, employing geopotential information from the
National Oceanic and Atmospheric Administration (NOAA) 20th Century
Reanalysis (NOAA 20CR). From 1958 onward the European Re-Analysis archives
(ERA-40 and ERA-Interim) available at the European Centre for Medium-Range
Weather Forecasts (ECMWF) are the main data sources. These are easier to use,
but pilot data still have to be interpolated to standard pressure levels.
Fractions of the same records distributed over different archives have been
merged, if necessary, taking care that the data remain traceable back to
their original sources. If possible, station IDs assigned by the World
Meteorological Organization (WMO) have been allocated to the station records.
For some records which have never been identified by a WMO ID, a local ID
above 100 000 has been assigned. The merged data set contains 37 wind records
longer than 70 years and 139 temperature records longer than 60 years. It can
be seen as a useful basis for further data processing steps, most notably
homogenization and gridding, after which it should be a valuable resource for
climatological studies.
Homogeneity adjustments for wind using the NOAA-20CR as a reference are
described in Ramella Pralungo and
Haimberger (2014). Reliable homogeneity adjustments for
temperature beyond 1958 using a surface-data-only reanalysis such as
NOAA-20CR as a reference have yet to be created.
All the archives and metadata files are available in ASCII and netCDF format
in the <i>PANGAEA</i> archive <a href="http://dx.doi.org/10.1594/PANGAEA.823617">doi:10.1594/PANGAEA.823617</a>
Spectroscopy of moderately high-redshift RCS-1 clusters
We present spectroscopic observations of 11 moderately high-redshift (z~0.7-
1.0) clusters from the first Red-Sequence Cluster Survey (RCS-1). We find
excellent agreement between the red-sequence estimated redshift and the
spectroscopic redshift, with a scatter of 10% at z>0.7. At the high-redshift
end (z>~0.9) of the sample, we find two of the systems selected are projections
of pairs of comparably rich systems, with red-sequences too close to
discriminate in (R-z') colour. In one of these systems, the two components are
close enough to be physically associated. For a subsample of clusters with
sufficient spectroscopic members, we examine the correlation between B_gcR
(optical richness) and the dynamical mass inferred from the velocity
dispersion. We find these measurements to be compatible, within the relatively
large uncertainties, with the correlation established at lower redshift for the
X-ray selected CNOC1 clusters and also for a lower redshift sample of RCS-1
clusters. Confirmation of this and calibration of the scatter in the relation
will require larger samples of clusters at these and higher redshifts.
[abridged]Comment: AJ accepted. 30 pages, 7 figures (figure 5 reduced quality
Confirming EIS Clusters. Optical and Infrared Imaging
Clusters of galaxies are important targets in observationally cosmology, as
they can be used both to study the evolution of the galaxies themselves and to
constrain cosmological parameters. Here we report on the first results of a
major effort to build up a sample of distant galaxy clusters to form the basis
for further studies within those fields. We search for simultaneous
overdensities in color and space to obtain supporting evidence for the reality
of the clusters. We find a confirmation rate for EIS clusters of 66%,
suggesting that a total of about 80 clusters with z>=0.6 are within reach using
the EIS cluster candidates.Comment: 4 pages, 2 figures, to appear in the proceedings of the IGRAP
International Conference 1999 on 'Clustering at high Redshift
Spectroscopic confirmation of clusters from the ESO imaging survey
We measure redshifts for 67 galaxies in the field of six cluster candidates
from the ESO Imaging Survey (EIS). The cluster candidates are selected in the
EIS patches C and D among those with estimated mean redshifts between 0.5 and
0.7. The observations were made with EFOSC2 at the 3.6m ESO telescope.
In the six candidate cluster fields, we identify 19 possible sets of 2 to 7
galaxies in redshift space. In order to establish which of the 19 sets are
likely to correspond to real dense systems we compare our counts with those
expected from a uniform distribution of galaxies with given luminosity
function. In order to take into account the effect of the Large Scale
Structure, we modulate the probability computed from the luminosity function
with random samplings of the Canada-France Redshift Survey.
We find that four out of six candidate EIS clusters are likely to correspond
to real systems in redshift space (> 95 % confidence level). Two of these
systems have mean redshift in agreement with the redshift estimate given by the
matched filter algorithm. The other two systems have significantly lower
redshifts.
We discuss the implications of our results in the context of our ongoing
research projects aimed at defining high-redshift optically-selected cluster
samples.Comment: To appear in A&A, main journal -- 12 pages, 9 figure
K-band Properties of Well-Sampled Groups of Galaxies
We use a sample of 55 groups and 6 clusters of galaxies ranging in mass from
7 x 10^11 Msun to 1.5 x 10^15 Msun to examine the correlation of the Ks-band
luminosity with mass discovered by Lin et al. (2003). We use the 2MASS catalog
and published redshifts to construct complete magnitude limited redshift
surveys of the groups. From these surveys we explore the IR photometric
properties of groups members including their IR color distribution and
luminosity function. Although we find no significant difference between the
group Ks luminosity function and the general field, there is a difference
between the color distribution of luminous group members and their counterparts
(generally background) in the field. There is a significant population of
luminous galaxies with H-Ks > 0.35 which are rarely, if ever, members of the
groups in our sample. The most luminous galaxies which populate the groups have
a very narrow range of IR color. Over the entire mass range covered by our
sample, the Ks luminosity increases with mass as L ~ M^(0.64 +/- 0.06) implying
that the mass-to-light ratio in the Ks-band increases with mass. The agreement
between this result and earlier investigations of essentially non-overlapping
sets of systems shows that this window in galaxy formation and evolution is
insensitive to the selection of the systems and to the details of the mass and
luminosity computations.Comment: 38 pages, 9 figures, 2 tables. Accepted for publication on
Astronomical Journa
On the Nature of the EIS Candidate Clusters: Confirmation of z<0.6 candidates
We use public V-band imaging data from the wide-angle surveys conducted by
the ESO Imaging Survey project (EIS) to further investigate the nature of the
EIS galaxy cluster candidates. These were originally identified by applying a
matched-filter algorithm which used positional and photometric data of the
galaxy sample extracted from the I-band survey images. In this paper, we apply
the same technique to the galaxy sample extracted from V-band data and compare
the new cluster detections with the original ones. We find that ~75% of the
low-redshift cluster candidates (z<0.6) are detected in both passbands and
their estimated redshifts show good agreement with the scatter in the redshift
differences being consistent with the estimated errors of the method. For the
``robust'' I-band detections the matching frequency approaches ~85%. We also
use the available (V-I) color to search for the red sequence of early-type
galaxies observed in rich clusters over a broad range of redshifts. This is
done by searching for a simultaneous overdensity in the three-dimensional
color-projected distance space. We find significant overdensities for ~75% of
the ``robust'' candidates with z_I<0.6. We find good agreement between the
characteristic color associated to the detected "red sequence" and that
predicted by passive evolution galaxy models for ellipticals at the redshift
estimated by the matched-filter. The results presented in this paper show the
usefulness of color data, even of two-band data, to both tentatively confirm
cluster candidates and to select possible cluster members for spectroscopic
observations. Based on the present results, we estimate that ~150 EIS clusters
with z_I<0.6 are real, making it one of the largest samples of galaxy clusters
in this redshift range currently available in the southern hemisphere.Comment: 11 pages, 10 figures, accepted for publication in A&
Memcomputing NP-complete problems in polynomial time using polynomial resources and collective states
Memcomputing is a novel non-Turing paradigm of computation that uses interacting memory cells (memprocessors for short) to store and process information on the same physical platform. It was recently proven mathematically that memcomputing machines have the same computational power of nondeterministic Turing machines. Therefore, they can solve NP-complete problems in polynomial time and, using the appropriate architecture, with resources that only grow polynomially with the input size. The reason for this computational power stems from properties inspired by the brain and shared by any universal memcomputing machine, in particular intrinsic parallelism and information overhead, namely, the capability of compressing information in the collective state of the memprocessor network. We show an experimental demonstration of an actual memcomputing architecture that solves the NP-complete version of the subset sum problem in only one step and is composed of a number of memprocessors that scales linearly with the size of the problem. We have fabricated this architecture using standard microelectronic technology so that it can be easily realized in any laboratory setting. Although the particular machine presented here is eventually limited by noise—and will thus require error-correcting codes to scale to an arbitrary number of memprocessors—it represents the first proof of concept of a machine capable of working with the collective state of interacting memory cells, unlike the present-day single-state machines built using the von Neumann architecture
The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined UZC and SSRS2
redshift surveys to construct a catalog of 1168 groups of galaxies; 411 of
these groups have 5 or more members within the redshift survey. The group
catalog covers 4.69 steradians and all groups exceed a number density contrast
threshold of 80. We demonstrate that the groups catalog is homogeneous across
the two underlying redshift surveys; the catalog of groups and their members
thus provides a basis for other statistical studies of the large-scale
distribution of groups and their physical properties. The median physical
properties of the groups are similar to those for groups derived from
independent surveys including the ESO Key Programme and the Las Campanas
Redshift Survey. We include tables of groups and their members.Comment: Accepted for publication on A
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