2,659 research outputs found
Detecting dark matter-dark energy coupling with the halo mass function
We use high-resolution simulations of large-scale structure formation to
analyze the effects of interacting dark matter and dark energy on the evolution
of the halo mass function. Using a chi-square likelihood analysis, we find
significant differences in the mass function between models of coupled dark
matter-dark energy and standard concordance cosmology Lambda-CDM out to
redshift z=1.5. We also find a preliminary indication that the Dark Energy
Survey should be able to distinguish these models from Lambda-CDM within its
mass and redshift contraints. While we can distinguish the effects of these
models from Lambda-CDM cosmologies with different fundamental parameters, DES
will require independent measurements of sigma-8 to confirm these effects.Comment: 5 pages, 3 figures, responded to referee comments, accepted by Ap
Abstract Ces\`aro spaces: Integral representations
The Ces\`aro function spaces , , have
received renewed attention in recent years. Many properties of are
known. Less is known about when the Ces\`aro operator takes its values
in a rearrangement invariant (r.i.) space other than . In this paper
we study the spaces via the methods of vector measures and vector
integration. These techniques allow us to identify the absolutely continuous
part of and the Fatou completion of ; to show that is
never reflexive and never r.i.; to identify when is weakly sequentially
complete, when it is isomorphic to an AL-space, and when it has the
Dunford-Pettis property. The same techniques are used to analyze the operator
; it is never compact but, it can be completely continuous.Comment: 21 page
Cluster magnetic fields from active galactic nuclei
Active galactic nuclei (AGN) found at the centers of clusters of galaxies are
a possible source for weak cluster-wide magnetic fields. To evaluate this
scenario, we present 3D adaptive mesh refinement MHD simulations of a cool-core
cluster that include injection of kinetic, thermal, and magnetic energy via an
AGN-powered jet. Using the MHD solver in FLASH 2, we compare several
sub-resolution approaches that link the estimated accretion rate as measured on
the simulation mesh to the accretion rate onto the central black hole and the
resulting feedback. We examine the effects of magnetized outflows on the
accretion history of the black hole and discuss the ability of these models to
magnetize the cluster medium.Comment: 4 pages, 2 figures, submitted to conference proceedings "The
Monster's Fiery Breath: Feedback in Groups, Galaxies, and Clusters
The Influence of AGN Feedback on Galaxy Cluster Observables
Galaxy clusters are valuable cosmological probes. However, cluster mass
estimates rely on observable quantities that are affected by complicated
baryonic physics in the intracluster medium (ICM), including feedback from
active galactic nuclei (AGN). Cosmological simulations have started to include
AGN feedback using subgrid models. In order to make robust predictions, the
systematics of different implementations and parametrizations need to be
understood. We have developed an AGN subgrid model in FLASH that supports a few
different black hole accretion models and feedback models. We use this model to
study the effect of AGN on X-ray cluster observables and its dependence on
model variations.Comment: minor error corrected, to appear in proceedings of the conference
"The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters",
June 2009, Madison, Wisconsi
The Impact of Type Ia Supernova Ejecta on Binary Companions
We present adaptive mesh refinement (AMR) hydrodynamical simulations of the
interaction between Type Ia supernovae and their companion stars within the
context of the single-degenerate model. Results for 3D red-giant companions
without binary evolution agree with previous 2D results by Marietta et al. We
also consider evolved helium-star companions in 2D. For a range of helium-star
masses and initial binary separations, we examine the mass unbound by the
interaction and the kick velocity delivered to the companion star. We find that
unbound mass versus separation obeys a power law with index between -3.1 and
-4.0, consistent with previous results for hydrogen-rich companions. Kick
velocity also obeys a power-law relationship with binary separation, but the
slope differs from those found for hydrogen-rich companions. Assuming accretion
via Roche-lobe overflow, we find that the unbound helium mass is consistent
with observational limits. Ablation (shock heating) appears to be more
important in removing gas from helium-star companions than from hydrogen-rich
ones, though stripping (momentum transfer) dominates in both cases.Comment: 6 pages, 2 figures, to appear in the proceedings of the conference
"Binary Star Evolution: Mass Loss, Accretion, and Mergers" at Mykonos,
Greece, June 22-25, 201
The Water Power Resolve
Contents: The State of Decision -- Maine\u27s Great Resources -- The Case of Ontario -- A Bit of Maine History -- Maine and New York -- Maine Women Endorse -- Value of State Aid. Not dated; circa 1920
A Direct Multigrid Poisson Solver for Oct-Tree Adaptive Meshes
We describe a finite-volume method for solving the Poisson equation on
oct-tree adaptive meshes using direct solvers for individual mesh blocks. The
method is a modified version of the method presented by Huang and Greengard
(2000), which works with finite-difference meshes and does not allow for shared
boundaries between refined patches. Our algorithm is implemented within the
FLASH code framework and makes use of the PARAMESH library, permitting
efficient use of parallel computers. We describe the algorithm and present test
results that demonstrate its accuracy.Comment: 10 pages, 6 figures, accepted by the Astrophysical Journal; minor
revisions in response to referee's comments; added char
Rings of Dark Matter in Collisions Between Clusters of Galaxies
Several lines of evidence suggest that the galaxy cluster Cl0024+17, an
apparently relaxed system, is actually a collision of two clusters, the
interaction occurring along our line of sight. Recent lensing observations
suggest the presence of a ring-like dark matter structure, which has been
interpreted as the result of such a collision. In this paper we present
-body simulations of cluster collisions along the line of sight to
investigate the detectability of such features. We use realistic dark matter
density profiles as determined from cosmological simulations. Our simulations
show a "shoulder" in the dark matter distribution after the collision, but no
ring feature even when the initial particle velocity distribution is highly
tangentially anisotropic (). Only when the initial
particle velocity distribution is circular do our simulations show such a
feature. Even modestly anisotropic velocity distributions are inconsistent with
the halo velocity distributions seen in cosmological simulations, and would
require highly fine-tuned initial conditions. Our investigation leaves us
without an explanation for the dark matter ring-like feature in Cl 0024+17
suggested by lensing observations.Comment: 7 pages (emulateapj), 9 figures. Expanded figures and text to match
accepted versio
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