938 research outputs found
Anisotropic Distribution of SDSS Satellite Galaxies: Planar (not Polar) Alignment
The distribution of satellite galaxies relative to isolated host galaxies in
the Sloan Digital Sky Survey (SDSS) is investigated. Host-satellite systems are
selected using three different methods, yielding samples of ~3300, ~1600, and
\~950 satellites. In the plane of the sky, the distributions of all three
samples show highly significant deviations from circular symmetry (> 99.99%, >
99.99%, and 99.79% confidence levels, respectively), and the degree of
anisotropy is a strong function of the projected radius, r_p, at which the
satellites are found. For r_p < 100 kpc, the SDSS satellites are aligned
preferentially with the major axes of the hosts. This is in stark contrast to
the Holmberg effect, in which satellites are aligned with the minor axes of
host galaxies. The degree of anisotropy in the distribution of the SDSS
satellites decreases with r_p and is consistent with an isotropic distribution
at of order the 1-sigma level for 250 kpc < r_p < 500 kpc.Comment: ApJ Letters (in press); Discussion section substantially revised,
SDSS DR3 included in the analysis, no significant changes to the result
The properties of highly luminous IRAS galaxies
From a complete sample of 154 galaxies identified with IRAS sources in a 304 sq deg area centered on the South Galactic Pole, a subsample of 58 galaxies with L sub IR/L sub B > 3 was chosen. Low resolution spectra were obtained for 30% of the subsample and redshifts and relative emission line intensities were derived. As a class these galaxies are very luminous with = 2.9 x 10 to the 11th power L sub 0 and (L sub IR) max = 1.3 x 10 to the 12th power L sub 0. CCD images and JHK photometry were obtained for many of the subsample. The galaxies are for the most part newly identified and are optically faint, with a majority showing evidence of a recent interaction. Radio continuum observations of all galaxies of the subsample were recently obtained at 20 cm VLA with about 75% being detected in a typical integration time of about 10 minutes
The ESO Slice Project (ESP) galaxy redshift survey: III. The Sample
The ESO Slice Project (ESP) is a galaxy redshift survey extending over about
23 square degrees, in a region near the South Galactic Pole. The survey is ~85%
complete to the limiting magnitude b_J=19.4 and consists of 3342 galaxies with
redshift determination.
The ESP survey is intermediate between shallow, wide angle samples and very
deep, one-dimensional pencil beams; the spanned volume is ~ 5 x 10^4 Mpc^3 at
the sensitivity peak (z ~ 0.1).
In this paper we present the description of the observations and of the data
reduction, the ESP redshift catalogue and the analysis of the quality of the
velocity determinations.Comment: 10 pages, 4 encapsulated figures, uses A&A LATEX; A&A Supplements in
press (June 1998 issue
Mapping cumulative noise from shipping to inform marine spatial planning
Including ocean noise in marine spatial planning requires predictions of noise levels on large spatiotemporal scales. Based on a simple sound transmission model and ship track data (Automatic Identification System, AIS), cumulative underwater acoustic energy from shipping was mapped throughout 2008 in the west Canadian Exclusive Economic Zone, showing high noise levels in critical habitats for endangered resident killer whales, exceeding limits of “good conservation status” under the EU Marine Strategy Framework Directive. Error analysis proved that rough calculations of noise occurrence and propagation can form a basis for management processes, because spending resources on unnecessary detail is wasteful and delays remedial action
Classification of Construction Projects
The final publication is available at World Academy of Science via https://waset.org/Publication/classification-of-construction-projects/10001697 © 2015, This unmodified version is made available under the CC BY-SA 2.0 https://creativecommons.org/licenses/by-sa/2.0/In order to address construction project requirements and specifications, scholars and practitioners need to establish taxonomy according to a scheme that best fits their need. While existing characterization methods are continuously being improved, new ones are devised to cover project properties which have not been previously addressed. One such method, the Project Definition Rating Index (PDRI), has received limited consideration strictly as a classification scheme. Developed by the Construction Industry Institute (CII) in 1996, the PDRI has been refined over the last two decades as a method for evaluating a project's scope definition completeness during front-end planning (FEP). The main contribution of this study is a review of practical project classification methods, and a discussion of how PDRI can be used to classify projects based on their readiness in the FEP phase. The proposed model has been applied to 59 construction projects in Ontario, and the results are discussed
The Opacity of Spiral Galaxy Disks VIII: Structure of the Cold ISM
The quantity of dust in a spiral disk can be estimated using the dust's
typical emission or the extinction of a known source. In this paper, we compare
two techniques, one based on emission and one on absorption, applied on
sections of fourteen disk galaxies. The two measurements reflect, respectively
the average and apparent optical depth of a disk section. Hence, they depend
differently on the average number and optical depth of ISM structures in the
disk. The small scale geometry of the cold ISM is critical for accurate models
of the overall energy budget of spiral disks. ISM geometry, relative
contributions of different stellar populations and dust emissivity are all free
parameters in galaxy Spectral Energy Distribution (SED) models; they are also
sometimes degenerate, depending on wavelength coverage. Our aim is to constrain
typical ISM geometry. The apparent optical depth measurement comes from the
number of distant galaxies seen in HST images through the foreground disk. We
measure the IR flux in images from the {\it Spitzer} Infrared Nearby Galaxy
Survey in the same section of the disk that was covered by HST. A physical
model of the dust is fit to the SED to estimate the dust surface density, mean
temperature, and brightness in these disk sections. The surface density is
subsequently converted into the average optical depth estimate. The two
measurements generally agree. The ratios between the measured average and
apparent optical depths of the disk sections imply optically thin clouds in
these disks. Optically thick disks, are likely to have more than a single cloud
along the line-of-sight.Comment: 31 pages, 5 figures, 4 tables, accepted for publication in A
Spatial and kinematic alignments between central and satellite halos
Based on a cosmological N-body simulation we analyze spatial and kinematic
alignments of satellite halos within six times the virial radius of group size
host halos (Rvir). We measure three different types of spatial alignment: halo
alignment between the orientation of the group central substructure (GCS) and
the distribution of its satellites, radial alignment between the orientation of
a satellite and the direction towards its GCS, and direct alignment between the
orientation of the GCS and that of its satellites. In analogy we use the
directions of satellite velocities and probe three further types of alignment:
the radial velocity alignment between the satellite velocity and connecting
line between satellite and GCS, the halo velocity alignment between the
orientation of the GCS and satellite velocities and the auto velocity alignment
between the satellites orientations and their velocities. We find that
satellites are preferentially located along the major axis of the GCS within at
least 6 Rvir (the range probed here). Furthermore, satellites preferentially
point towards the GCS. The most pronounced signal is detected on small scales
but a detectable signal extends out to 6 Rvir. The direct alignment signal is
weaker, however a systematic trend is visible at distances < 2 Rvir. All
velocity alignments are highly significant on small scales. Our results suggest
that the halo alignment reflects the filamentary large scale structure which
extends far beyond the virial radii of the groups. In contrast, the main
contribution to the radial alignment arises from the adjustment of the
satellite orientations in the group tidal field. The projected data reveal good
agreement with recent results derived from large galaxy surveys. (abridged)Comment: accepted for publication in Ap
Reconstructing the Triaxial Shapes of Dark Matter Halos from the Anisotropic Spatial Distributions of their Substructures in the Concordance Cosmology
We develop an algorithm to reconstruct the triaxial shapes of dark matter
halos from the anisotropic spatial distributions of their substructures for the
concordance background cosmology. First, we construct an analytic model for the
anisotropic spatial distribution of dark halo substructures under the
assumption that the tidal field with non-zero trace in the triaxial mass
distribution of the host halos generates the substructure bulk motions toward
the major principal axes of the hosts. Our analytic model implies that the
degree of anisotropy depends sensitively on the triaxiality of the host halos
as well as the correlation between the substructure locations and the tidal
shear field. Second, we set the axis ratios of the triaxial host halos as free
parameters in the analytic model, fit the model to the numerical results from
high-resolution N-body simulation of the concordance cosmology, and reconstruct
the two axis-ratios of the host halos from the best-fit values of the free
parameters. The comparison of the reconstructed axis ratios with the numerical
results reveals a good agreement. Finally, we conclude that our analytic model
may provide a physical understanding of the anisotropic spatial distribution of
dark halo substructures and a new way to reconstruct in principle the triaxial
shapes of dark matter halos from the observables.Comment: accepted for publication in ApJ, discussion on the limitation of the
algorithm added, typos and mistakes corrected, 14 pages, 12 figure
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