149 research outputs found
Cosmological Simulations on a Grid of Computers
The work presented in this paper aims at restricting the input parameter
values of the semi-analytical model used in GALICS and MOMAF, so as to derive
which parameters influence the most the results, e.g., star formation, feedback
and halo recycling efficiencies, etc. Our approach is to proceed empirically:
we run lots of simulations and derive the correct ranges of values. The
computation time needed is so large, that we need to run on a grid of
computers. Hence, we model GALICS and MOMAF execution time and output files
size, and run the simulation using a grid middleware: DIET. All the complexity
of accessing resources, scheduling simulations and managing data is harnessed
by DIET and hidden behind a web portal accessible to the users.Comment: Accepted and Published in AIP Conference Proceedings 1241, 2010,
pages 816-82
Dynamic cosmography of the local Universe: Laniakea and five more watershed superclusters
This article delivers the dynamical cosmography of the Local Universe within
z=0.1 (1 giga light-years). We exploit the gravitational velocity field
computed using the CosmicFlows-4 catalog of galaxy distances to delineate
superclusters as watersheds, publishing for the first time their size, shape,
main streams of matter and the location of their central attractor. Laniakea,
our home supercluster's size is confirmed to be 2 (Mpc
). Five more known superclusters are now dynamically defined in the
same way: Apus, Hercules, Lepus, Perseus-Pisces and Shapley. Also, the central
repellers of the Bootes and Sculptor voids are found and the Dipole and Cold
Spot repellers now appear as a single gigantic entity. Interestingly the
observed superclusters are an order of magnitude larger than the theoretical
ones predicted by cosmological CDM simulations.Comment: 8 pages, 4 figures, 1 table, accepted in A&A (AA/2023/46802
Cosmological Simulations using Grid Middleware
One way to access the aggregated power of a collection of heterogeneous
machines is to use a grid middleware, such as DIET, GridSolve or NINF. It
addresses the problem of monitoring the resources, of handling the submissions
of jobs and as an example the inherent transfer of input and output data, in
place of the user.
In this paper we present how to run cosmological simulations using the RAMSES
application along with the DIET middleware. We will describe how to write the
corresponding DIET client and server. The remainder of the paper is organized
as follows: Section 2 presents the DIET middleware. Section 3 describes the
RAMSES cosmological software and simulations, and how to interface it with
DIET. We show how to write a client and a server in Section 4. Finally, Section
5 presents the experiments realized on Grid'5000, the French Research Grid, and
we conclude in Section 6.Comment: submitted Nov 200
The mid-infrared Tully-Fisher relation: Spitzer Surface Photometry
The availability of photometric imaging of several thousand galaxies with the
Spitzer Space Telescope enables a mid-infrared calibration of the correlation
between luminosity and rotation in spiral galaxies. The most important
advantage of the new calibration in the 3.6 micron band, IRAC ch.1, is
photometric consistency across the entire sky. Additional advantages are
minimal obscuration, observations of flux dominated by old stars, and
sensitivity to low surface brightness levels due to favorable backgrounds.
Through Spitzer cycle 7 roughly 3000 galaxies had been observed and images of
these are available at the Spitzer archive. In cycle 8 a program called Cosmic
Flows with Spitzer has been initiated that will increase by 1274 the available
sample of spiral galaxies with inclinations greater than 45 degrees from
face-on suitable for distance measurements. This paper describes procedures
based on the photometry package Archangel that are being employed to analyze
both the archival and the new data in a uniform way. We give results for 235
galaxies, our calibrator sample for the Tully-Fisher relation. Galaxy
magnitudes are determined with uncertainties held below 0.05 mag for normal
spiral systems. A subsequent paper will describe the calibration of the [3.6]
luminosity-rotation relation.Comment: Accepted for publication in The Astronomical Journal, 12 pages, 9
figure
Calving photocensus of the Rivière George Caribou Herd and comparison with an independent census
Vertical photographs of the calving grounds have been used since 1984 to estimate the caribou (Rangifer tarandus) population of the Rivière George Caribou Herd (RGCH) in Northern Québec and Labrador. In spite of large confidence intervals, the 1984 and 1988 estimates suggested that the herd stabilized at more than 650 000 caribou (fall estimate including calves) making the RGCH the largest caribou herd in the world. Between 1984 and 1990, studies suggested that the former rapid growth of the herd deteriorated the calving and summer habitats. This poor habitat quality affected physical condition, pregnancy rate and calf survival. It was important to have a valid estimate of the herd size and a photocensus was done in June 1993. Contrary to previous censuses, a slightly different sampling design was applied in 1993. Two methods were used to estimate the number of females in the June population. In the first method, the number of females was derived from the estimated number of calves on the photographs and from the June female/calf ratio. The second method was used in the previous census and is based on the number of adults on the photos and on the June female/adult ratio. It is suggested that the first method of estimating female abundance in June is better due to sampling problems associated with a strong adult sex segregation during calving. From the first method, the herd size in October 1993 was estimated at 583 829 adults (±33.79%) and at 749 869 caribou including calves (±33.15%) while the second method provided estimates of 764 221 adults (±23.55%) and 981 565 caribou including calves (±22.64%). It was possible to compare those population estimates with an independent census. In July 1993, an oblique photocensus of the post-calving aggregations was conducted by Russell et al. (1996). A new analysis of their raw data provided an estimate of 608 384 adults (±14.35%). Both estimates from the June and July photocensus were combined. From the first and second method respectively, combined herd size estimates were 775 891 (±13.40%) and 823 375 (±12.36%) caribou including calves. The management implications are discussed and it is emphasized that the herd is still underharvested
Cosmicflows-2: SNIa Calibration and H0
The construction of the Cosmicflows-2 compendium of distances involves the
merging of distance measures contributed by the following methods: (Cepheid)
Period-Luminosity, Tip of the Red Giant Branch (TRGB), Surface Brightness
Fluctuation (SBF), Luminosity-Linewidth (TF), Fundamental Plane (FP), and Type
Ia supernova (SNIa). The method involving SNIa is at the top of an
interconnected ladder, providing accurate distances to well beyond the expected
range of distortions to Hubble flow from peculiar motions. In this paper, the
SNIa scale is anchored by 36 TF spirals with Cepheid or TRGB distances, 56 SNIa
hosts with TF distances, and 61 groups or clusters hosting SNIa with Cepheid,
SBF, TF, or FP distances. With the SNIa scale zero point set, a value of the
Hubble Constant is evaluated over a range of redshifts 0.03 < z < 0.5, assuming
a cosmological model with Omega_m = 0.27 and Omega_Lambda = 0.73. The value
determined for the Hubble Constant is H0 = 75.9 \pm 3.8 km s-1 Mpc-1.Comment: Accepted for publication in The Astrophysical Journal. 11 pages,
8Figures, 5 Table
The Calibration of the WISE W1 and W2 Tully-Fisher Relation
In order to explore local large-scale structures and velocity fields,
accurate galaxy distance measures are needed. We now extend the well-tested
recipe for calibrating the correlation between galaxy rotation rates and
luminosities -- capable of providing such distance measures -- to the all-sky,
space-based imaging data from the Wide-field Infrared Survey Explorer (WISE) W1
(m) and W2 (m) filters. We find a linewidth to absolute
magnitude correlation (known as the Tully-Fisher Relation, TFR) of
(0.54
magnitudes rms) and (0.56 magnitudes rms) from 310 galaxies in 13 clusters. We update the
I-band TFR using a sample 9% larger than in Tully & Courtois (2012). We derive
(0.46 magnitudes
rms). The WISE TFRs show evidence of curvature. Quadratic fits give
(0.52 magnitudes rms) and (0.55
magnitudes rms). We apply an I-band -- WISE color correction to lower the
scatter and derive
and (both 0.46
magnitudes rms). Using our three independent TFRs (W1 curved, W2 curved and
I-band), we calibrate the UNION2 supernova Type Ia sample distance scale and
derive (stat) (sys) kms Mpc with 4%
total error.Comment: 22 page, 21 figures, accepted to ApJ, Table 1 data at
http://spartan.srl.caltech.edu/~neill/tfwisecal/table1.tx
3D Velocity and Density Reconstructions of the Local Universe with Cosmicflows-1
This paper presents an analysis of the local peculiar velocity field based on
the Wiener Filter reconstruction method. We used our currently available
catalog of distance measurements containing 1,797 galaxies within 3000 km/s:
Cosmicflows-1. The Wiener Filter method is used to recover the full 3D peculiar
velocity field from the observed map of radial velocities and to recover the
underlying linear density field. The velocity field within a data zone of 3000
km/s is decomposed into a local component that is generated within the data
zone and a tidal one that is generated by the mass distribution outside that
zone. The tidal component is characterized by a coherent flow toward the
Norma-Hydra-Centaurus (Great Attractor) region while the local component is
dominated by a flow toward the Virgo Cluster and away from the Local Void. A
detailed analysis shows that the local flow is predominantly governed by the
Local Void and the Virgo Cluster plays a lesser role. The analysis procedure
was tested against a mock catalog. It is demonstrated that the Wiener Filter
accurately recovers the input velocity field of the mock catalog on the scale
of the extraction of distances and reasonably recovers the velocity field on
significantly larger scales. The Bayesian Wiener Filter reconstruction is
carried out within the ?CDM WMAP5 framework. The Wiener Filter reconstruction
draws particular attention to the importance of voids in proximity to our
neighborhood. The prominent structure of the Local Supercluster is wrapped in a
horseshoe collar of under density with the Local Void as a major component.Comment: Accepted for ApJ, August 6, 201
Cosmicflows-2: I-band Luminosity - HI Linewidth Calibration
In order to measure distances with minimal systematics using the correlation
between galaxy luminosities and rotation rates it is necessary to adhere to a
strict and tested recipe. We now derive a measure of rotation from a new
characterization of the width of a neutral Hydrogen line profile. Additionally,
new photometry and zero point calibration data are available. Particularly the
introduction of a new linewidth parameter necessitates the reconstruction and
absolute calibration of the luminosity-linewidth template. The slope of the new
template is set by 267 galaxies in 13 clusters. The zero point is set by 36
galaxies with Cepheid or Tip of the Red Giant Branch distances. Tentatively, we
determine H0 = 75 km s-1 Mpc-1. Distances determined using the
luminosity-linewidth calibration will contribute to the distance compendium
Cosmicflows-2.Comment: Accepted for publication in The Astrophysical Journal, 27 pages, 18
figure
Our Peculiar Motion Away from the Local Void
The peculiar velocity of the Local Group of galaxies manifested in the Cosmic
Microwave Background dipole is found to decompose into three dominant
components. The three components are clearly separated because they arise on
distinct spatial scales and are fortuitously almost orthogonal in their
influences. The nearest, which is distinguished by a velocity discontinuity at
~7 Mpc, arises from the evacuation of the Local Void. We lie in the Local Sheet
that bounds the void. Random motions within the Local Sheet are small. Our
Galaxy participates in the bulk motion of the Local Sheet away from the Local
Void. The component of our motion on an intermediate scale is attributed to the
Virgo Cluster and its surroundings, 17 Mpc away. The third and largest
component is an attraction on scales larger than 3000 km/s and centered near
the direction of the Centaurus Cluster. The amplitudes of the three components
are 259, 185, and 455 km/s, respectively, adding collectively to 631 km/s in
the reference frame of the Local Sheet. Taking the nearby influences into
account causes the residual attributed to large scales to align with observed
concentrations of distant galaxies and reduces somewhat the amplitude of motion
attributed to their pull. On small scales, in addition to the motion of our
Local Sheet away from the Local Void, the nearest adjacent filament, the Leo
Spur, is seen to be moving in a direction that will lead to convergence with
our filament. Finally, a good distance to an isolated galaxy within the Local
Void reveals that this dwarf system has a motion of at least 230 km/s away from
the void center. Given the velocities expected from gravitational instability
theory in the standard cosmological paradigm, the distance to the center of the
Local Void must be at least 23 Mpc from our position. The Local Void is large!Comment: Tentatively scheduled for Astrophysical Journal, 676 (March 20),
2008. 18 figures, 3 tables including web link for 2 tables, web links to 2
video
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