91 research outputs found
RCS043938-2904.9: A New Rich Cluster of Galaxies at z=0.951
We present deep I, J_s, K_s imaging and optical spectroscopy of the newly
discovered Red-Sequence Cluster Survey cluster RCS043938-2904.9. This cluster,
drawn from an extensive preliminary list, was selected for detailed study on
the basis of its apparent optical richness. Spectroscopy of 11 members places
the cluster at z=0.951 +- 0.006, and confirms the photometric redshift estimate
from the (R-z) color-magnitude diagram. Analysis of the infrared imaging data
demonstrates that the cluster is extremely rich, with excess counts in the
Ks-band exceeding the expected background counts by 9 sigma. The properties of
the galaxies in RCS043938-2904.9 are consistent with those seen in other
clusters at similar redshifts. Specifically, the red-sequence color, slope and
scatter, and the size-magnitude relation of these galaxies are all consistent
with that seen in the few other high redshift clusters known, and indeed are
consistent with appropriately evolved properties of local cluster galaxies. The
apparent consistency of these systems implies that the rich, high-redshift RCS
clusters are directly comparable to the few other systems known at z ~ 1, most
of which have been selected on the basis of X-ray emission.Comment: 12 pages, 1 color figure. Accepted for publication on The ApJ Letter
Quasars Clustering at z approx 3 on Scales less sim 10 h^{-1} Mpc
We test the hypothesis whether high redshift QSOs would preferentially appear
in small groups or pairs, and if they are associated with massive, young
clusters. We carried out a photometric search for \Ly emitters on scales
Mpc, in the fields of a sample of 47 known
QSOs. Wide and narrow band filter color-magnitude diagrams were generated for
each of the fields. A total of 13 non resolved objects with a
significant color excess were detected as QSO candidates at a redshift similar
to that of the target. All the candidates are significantly fainter than the
reference QSOs, with only 2 of them within 2 magnitudes of the central object.
Follow-up spectroscopic observations have shown that 5, i.e., about 40% of the
candidates, are QSOs at the same redshift of the target; 4 are QSOs at
different z (two of them probably being a lensed pair at z = 1.47); 2
candidates are unresolved HII galaxies at z0.3; one unclassified and one
candidate turned out to be a CCD flaw. These data indicate that at least 10% of
the QSOs at z3 do have companions.
We have also detected a number of resolved, rather bright \Ly Emitter
Candidates. Most probably a large fraction of them might be bright galaxies
with [OII] emission, at z 0.3. The fainter population of our
candidates corresponds to the current expectations. Thus, there are no strong
indication for the existence of an overdensity of \Ly galaxies brighter than m
25 around QSOs at 3.Comment: 29 pages, 8 figures, tar gzip LaTex file, accepted to appear in Ap
Quantum deformations of associative algebras and integrable systems
Quantum deformations of the structure constants for a class of associative
noncommutative algebras are studied. It is shown that these deformations are
governed by the quantum central systems which has a geometrical meaning of
vanishing Riemann curvature tensor for Christoffel symbols identified with the
structure constants. A subclass of isoassociative quantum deformations is
described by the oriented associativity equation and, in particular, by the
WDVV equation. It is demonstrated that a wider class of weakly (non)associative
quantum deformations is connected with the integrable soliton equations too. In
particular, such deformations for the three-dimensional and
infinite-dimensional algebras are described by the Boussinesq equation and KP
hierarchy, respectively.Comment: Numeration of the formulas is correcte
ACS Observations of a Strongly Lensed Arc in a Field Elliptical
We report the discovery of a strongly lensed arc system around a field
elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys
(ACS) images of a parallel field observed during NICMOS observations of the HST
Ultra-Deep Field. The ACS parallel data comprise deep imaging in the F435W,
F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 1.6 arcsec
from the galaxy center and subtends about 120 deg. Spectroscopic follow-up at
Magellan Observatory yields a redshift z=0.6174 for the lensing galaxy, and we
photometrically estimate z_phot = 2.4\pm0.3 for the arc. We also identify a
likely counter-arc at a radius of 0.6 arcsec, which shows structure similar to
that seen in the main arc. We model this system and find a good fit to an
elliptical isothermal potential of velocity dispersion
\kms, the value expected from the fundamental plane, and some external shear.
Several other galaxies in the field have colors similar to the lensing galaxy
and likely make up a small group.Comment: Accepted for publication in ApJ Letters. 10 pages, 3 figures. Figures
have been degraded to meet size limit; a higher resolution version and
addtional pictures available at http://acs.pha.jhu.edu/~jpb/UDFparc
The structure of 2D semi-simple field theories
I classify all cohomological 2D field theories based on a semi-simple complex
Frobenius algebra A. They are controlled by a linear combination of
kappa-classes and by an extension datum to the Deligne-Mumford boundary. Their
effect on the Gromov-Witten potential is described by Givental's Fock space
formulae. This leads to the reconstruction of Gromov-Witten invariants from the
quantum cup-product at a single semi-simple point and from the first Chern
class, confirming Givental's higher-genus reconstruction conjecture. The proof
uses the Mumford conjecture proved by Madsen and Weiss.Comment: Small errors corrected in v3. Agrees with published versio
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Results of the ontology alignment evaluation initiative 2019
The Ontology Alignment Evaluation Initiative (OAEI) aims at comparing ontology matching systems on precisely defined test cases. These test cases can be based on ontologies of different levels of complexity (from simple thesauri to expressive OWL ontologies) and use different evaluation modalities (e.g., blind evaluation, open evaluation, or consensus). The OAEI 2019 campaign offered 11 tracks with 29 test cases, and was attended by 20 participants. This paper is an overall presentation of that campaign
Spectroscopic Characterization of Galaxy Clusters in RCS-1: Spectroscopic Confirmation, Redshift Accuracy, and Dynamical Mass–Richness Relation
We present follow-up spectroscopic observations of galaxy clusters from the first Red-sequence Cluster Survey (RCS-1). This work focuses on two samples, a lower redshift sample of ∼30 clusters ranging in redshift from z ∼ 0.2–0.6 observed with multiobject spectroscopy (MOS) on 4–6.5-m class telescopes and a z ∼ 1 sample of ∼10 clusters 8-m class telescope observations. We examine the detection efficiency and redshift accuracy of the now widely used red-sequence technique for selecting clusters via overdensities of red-sequence galaxies. Using both these data and extended samples including previously published RCS-1 spectroscopy and spectroscopic redshifts from SDSS, we find that the red-sequence redshift using simple two-filter cluster photometric redshifts is accurate to σz ≈ 0.035(1 + z) in RCS-1. This accuracy can potentially be improved with better survey photometric calibration. For the lower redshift sample, ∼5 per cent of clusters show some (minor) contamination from secondary systems with the same red-sequence intruding into the measurement aperture of the original cluster. At z ∼ 1, the rate rises to ∼20 per cent. Approximately ten per cent of projections are expected to be serious, where the two components contribute significant numbers of their red-sequence galaxies to another cluster. Finally, we present a preliminary study of the mass–richness calibration using velocity dispersions to probe the dynamical masses of the clusters. We find a relation broadly consistent with that seen in the local universe from the WINGS sample at z ∼ 0.05
Discovery of two M32 twins in Abell 1689
The M31 satellite galaxy M32 has long been considered an object of unique
properties, being the most extreme example of the very rare compact elliptical
galaxy class. Here we present the spectroscopic discovery of two M32 twins in
the massive galaxy cluster Abell 1689. As these objects are so rare, this is an
important step towards a better understanding of the nature of compact
galaxies. The two M32 twins had first been detected within our photometric
search for ultra compact dwarf galaxy (UCDs) candidates in A1689 (Mieske et al.
2004) with the Advanced Camera for Surveys (ACS). Their luminosities (M_V ~ -17
mag) are very similar to M32 and their surface brightness profiles are
consistent with that of M32 projected to A1689's distance. From our ACS imaging
we detect several fainter compact galaxy candidates with luminosities
intermediate between M32 and the Fornax UCDs. If spectroscopically confirmed as
cluster members, this would almost close the gap in the magnitude-surface
brightness plane between the region of UCDs and the compact ellipticals,
implying a sequence of faint compact galaxies well separated from that of dwarf
ellipticals.Comment: 5 pages, 5 figures, accepted for publication in A&A letter
The XMM-LSS survey: the Class 1 cluster sample over the initial 5 square degrees and its cosmological modelling
We present a sample of 29 galaxy clusters from the XMM-LSS survey over an
area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which
represent about half of the X-ray clusters identified in the region, follow
well defined X-ray selection criteria and are all spectroscopically confirmed.
For all clusters, we provide X-ray luminosities and temperatures as well as
masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the
objects being groups with a temperature below 2 keV. Our L-T(z) relation points
toward self-similar evolution, but does not exclude other physically plausible
models. Assuming that cluster scaling laws follow self-similar evolution, our
number density estimates up to z=1 are compatible with the predictions of the
concordance cosmology and with the findings of previous ROSAT surveys. Our well
monitored selection function allowed us to demonstrate that the inclusion of
selection effects is essential for the correct determination of the evolution
of the L-T relation, which may explain the contradictory results from previous
studies. Extensive simulations show that extending the survey area to 10deg2
has the potential to exclude the non-evolution hypothesis, but that constraints
on more refined ICM models will probably be limited by the large intrinsic
dispersion of the L-T relation. We further demonstrate that increasing the
dispersion in the scaling laws increases the number of detectable clusters,
hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and
T(M,z)] in the cosmological interpretation of the cluster number counts. We
provide useful empirical formulae for the cluster mass-flux and mass-count-rate
relations as well as a comparison between the XMM-LSS mass sensitivity and that
of forthcoming SZ surveys.Comment: Accepted for publication by MNRAS. Full resolution images as well as
additional cluster data are available through a dedicated database at
http://l3sdb.in2p3.fr:8080/l3sdb
Computability and dynamical systems
In this paper we explore results that establish a link between dynamical
systems and computability theory (not numerical analysis). In the last few decades,
computers have increasingly been used as simulation tools for gaining insight into
dynamical behavior. However, due to the presence of errors inherent in such numerical
simulations, with few exceptions, computers have not been used for the
nobler task of proving mathematical results. Nevertheless, there have been some recent
developments in the latter direction. Here we introduce some of the ideas and
techniques used so far, and suggest some lines of research for further work on this
fascinating topic
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