2,559 research outputs found
The Las Campanas Distant Cluster Survey -- The Correlation Function
We present the first non-local (z>0.2) measurement of the cluster-cluster
spatial correlation length, using data from the Las Campanas Distant Cluster
Survey (LCDCS). We measure the angular correlation function for
velocity-dispersion limited subsamples of the catalog at estimated redshifts of
0.35<z_{est}<0.575, and derive spatial correlation lengths for these clusters
via the cosmological Limber equation. The correlation lengths that we measure
for clusters in the LCDCS are consistent both with local results for the APM
cluster catalog and with theoretical expectations based upon the Virgo
Consortium Hubble Volume simulations and the analytic predictions. Despite
samples containing over 100 clusters, our ability to discriminate between
cosmological models is limited because of statistical uncertainty.Comment: 7 pages, 4 figures, accepted to ApJ (v571, May 20, 2002
Galaxy bimodality versus stellar mass and environment
We analyse a z<0.1 galaxy sample from the Sloan Digital Sky Survey focusing
on the variation of the galaxy colour bimodality with stellar mass and
projected neighbour density Sigma, and on measurements of the galaxy stellar
mass functions. The characteristic mass increases with environmental density
from about 10^10.6 Msun to 10^10.9 Msun (Kroupa IMF, H_0=70) for Sigma in the
range 0.1--10 per Mpc^2. The galaxy population naturally divides into a red and
blue sequence with the locus of the sequences in colour-mass and
colour-concentration index not varying strongly with environment. The fraction
of galaxies on the red sequence is determined in bins of 0.2 in log Sigma and
log mass (12 x 13 bins). The red fraction f_r generally increases continuously
in both Sigma and mass such that there is a unified relation: f_r =
F(Sigma,mass). Two simple functions are proposed which provide good fits to the
data. These data are compared with analogous quantities in semi-analytical
models based on the Millennium N-body simulation: the Bower et al. (2006) and
Croton et al. (2006) models that incorporate AGN feedback. Both models predict
a strong dependence of the red fraction on stellar mass and environment that is
qualitatively similar to the observations. However, a quantitative comparison
shows that the Bower et al. model is a significantly better match; this appears
to be due to the different treatment of feedback in central galaxies.Comment: 19 pages, 17 figures; accepted by MNRAS, minor change
An Isocurvature CDM Cosmogony. II. Observational Tests
A companion paper presents a worked model for evolution through inflation to
initial conditions for an isocurvature model for structure formation. It is
shown here that the model is consistent with the available observational
constraints that can be applied without the help of numerical simulations. The
model gives an acceptable fit to the second moments of the angular fluctuations
in the thermal background radiation and the second through fourth moments of
the measured large-scale fluctuations in galaxy counts, within the possibly
significant uncertainties in these measurements. The cluster mass function
requires a rather low but observationally acceptable mass density,
0.1\lsim\Omega\lsim 0.2 in a cosmologically flat universe. Galaxies would be
assembled earlier in this model than in the adiabatic version, an arguably good
thing. Aspects of the predicted non-Gaussian character of the anisotropy of the
thermal background radiation in this model are discussed.Comment: 14 pages, 3 postscript figures, uses aas2pp4.st
The Clustering of AGN in the Sloan Digital Sky Survey
We present the two--point correlation function (2PCF) of narrow-line active
galactic nuclei (AGN) selected within the First Data Release of the Sloan
Digital Sky Survey. Using a sample of 13605 AGN in the redshift range 0.055 < z
< 0.2, we find that the AGN auto--correlation function is consistent with the
observed galaxy auto--correlation function on scales 0.2h^{-1}Mpc to
>100h^{-1}Mpc. The AGN hosts trace an intermediate population of galaxies and
are not detected in either the bluest (youngest) disk--dominated galaxies or
many of the reddest (oldest) galaxies. We show that the AGN 2PCF is dependent
on the luminosity of the narrow [OIII] emission line (L_{[OIII]}), with low
L_{[OIII]} AGN having a higher clustering amplitude than high L_{[OIII]} AGN.
This is consistent with lower activity AGN residing in more massive galaxies
than higher activity AGN, and L_{[OIII]} providing a good indicator of the
fueling rate. Using a model relating halo mass to black hole mass in
cosmological simulations, we show that AGN hosted by ~ 10^{12} M_{odot} dark
matter halos have a 2PCF that matches that of the observed sample. This mass
scale implies a mean black hole mass for the sample of M_{BH} ~ 10^8 M_{odot}.Comment: 5 pages, 4 figures. Accepted for publication in ApJ
High-rate, high-fidelity entanglement of qubits across an elementary quantum network
We demonstrate remote entanglement of trapped-ion qubits via a
quantum-optical fiber link with fidelity and rate approaching those of local
operations. Two Sr qubits are entangled via the polarization
degree of freedom of two photons which are coupled by high-numerical-aperture
lenses into single-mode optical fibers and interfere on a beamsplitter. A novel
geometry allows high-efficiency photon collection while maintaining unit
fidelity for ion-photon entanglement. We generate remote Bell pairs with
fidelity at an average rate (success
probability ).Comment: v2 updated to include responses to reviewers, as published in PR
Projection, Spatial Correlations, and Anisotropies in a Large and Complete Sample of Abell Clusters
An analysis of R >= 1 Abell clusters is presented for samples containing
recent redshifts from the MX Northern Abell Cluster Survey. The newly obtained
redshifts from the MX Survey as well as those from the ESO Nearby Abell Cluster
Survey (ENACS) provide the necessary data for the largest magnitude-limited
correlation analysis of rich clusters in the entire sky (excluding the galactic
plane) to date. We find 19.4 <= r_0 <= 23.3 h^-1Mpc, -1.92 <= gamma <= -1.83
for four different subsets of Abell/ACO clusters, including a large sample
(N=104) of cD clusters. We have used this dataset to look for line-of-sight
anisotropies within the Abell/ACO catalogs. We show that the strong
anisotropies present in previously studied Abell cluster datasets are not
present in our R >= 1 samples. There are, however, indications of residual
anisotropies which we show are the result of two elongated superclusters, Ursa
Majoris and Corona Borealis, whose axes lie near the line-of-sight. After
rotating these superclusters so that their semi-major axes are prependicular to
the line-of-sight, we find no anisotropies as indicated by the correlation
function. The amplitude and slope of the two-point correlation function remain
the same before and after these rotations. We also remove a subset of R = 1
Abell/ACO clusters that show sizable foreground/background galaxy contamination
and again find no change in the amplitude or slope of the correlation function.
We conclude that the correlation length of R >= 1 Abell clusters is not
artificially enhanced by line-of-sight anisotropies.Comment: 37 pages, 8 figures, AASTeX Accepted for publication in Ap
Clustering of loose groups and galaxies from the Perseus--Pisces Survey
We investigate the clustering properties of loose groups in the
Perseus--Pisces redshift Survey (PPS). Previous analyses based on CfA and SSRS
surveys led to apparently contradictory results. We investigate the source of
such discrepancies, finding satisfactory explanations for them. Furthermore, we
find a definite signal of group clustering, whose amplitude exceeds the
amplitude of galaxy clustering (,
for the most significant case; distances are
measured in \hMpc). Groups are identified with the adaptive
Friends--Of--Friends (FOF) algorithms HG (Huchra \& Geller 1982) and NW
(Nolthenius \& White 1987), systematically varying all search parameters.
Correlation strenght is especially sensitive to the sky--link (increasing
for stricter normalization ), and to the (depth \mlim of the) galaxy
data. It is only moderately dependent on the galaxy luminosity function
, while it is almost insensitive to the redshift--link (both to
the normalization and to the scaling recipes HG or NW).Comment: 28 pages (LaTeX aasms4 style) + 5 Postscript figures ; ApJ submitted
on May 4th, 1996; group catalogs available upon request
([email protected]
The Bright SHARC Survey: The Cluster Catalog
We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT
Cluster) Survey, which is an objective search for serendipitously detected
extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC
Survey covers an area of 178.6 sq.deg and has yielded 374 extended sources. We
discuss the X-ray data reduction, the candidate selection and present results
from our on-going optical follow-up campaign. The optical follow-up
concentrates on the brightest 94 of the 374 extended sources and is now 97%
complete. We have identified thirty-seven clusters of galaxies, for which we
present redshifts and luminosities. The clusters span a redshift range of
0.0696<z<0.83 and a luminosity range of 0.065<Lx<8.3e44 erg/s [0.5-2.0 keV]
(assuming Ho = 50 km/s/Mpc and qo=0.5). Twelve of the clusters have redshifts
greater than z=0.3, eight of which are at luminosities brighter than Lx=3e44
erg/s. Seventeen of the 37 optically confirmed Bright SHARC clusters have not
been listed in any previously published catalog. We also report the discovery
of three candidate ``fossil groups'' of the kind proposed by Ponman et al.
(1994).Comment: Minor revisions: References updated and typos corrected. Shortened by
use of emulateapj.st
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