1,422 research outputs found
A Multi-Code Analysis Toolkit for Astrophysical Simulation Data
The analysis of complex multiphysics astrophysical simulations presents a
unique and rapidly growing set of challenges: reproducibility, parallelization,
and vast increases in data size and complexity chief among them. In order to
meet these challenges, and in order to open up new avenues for collaboration
between users of multiple simulation platforms, we present yt (available at
http://yt.enzotools.org/), an open source, community-developed astrophysical
analysis and visualization toolkit. Analysis and visualization with yt are
oriented around physically relevant quantities rather than quantities native to
astrophysical simulation codes. While originally designed for handling Enzo's
structure adaptive mesh refinement (AMR) data, yt has been extended to work
with several different simulation methods and simulation codes including Orion,
RAMSES, and FLASH. We report on its methods for reading, handling, and
visualizing data, including projections, multivariate volume rendering,
multi-dimensional histograms, halo finding, light cone generation and
topologically-connected isocontour identification. Furthermore, we discuss the
underlying algorithms yt uses for processing and visualizing data, and its
mechanisms for parallelization of analysis tasks.Comment: 18 pages, 6 figures, emulateapj format. Resubmitted to Astrophysical
Journal Supplement Series with revisions from referee. yt can be found at
http://yt.enzotools.org
Report from the Tri-Agency Cosmological Simulation Task Force
The Tri-Agency Cosmological Simulations (TACS) Task Force was formed when
Program Managers from the Department of Energy (DOE), the National Aeronautics
and Space Administration (NASA), and the National Science Foundation (NSF)
expressed an interest in receiving input into the cosmological simulations
landscape related to the upcoming DOE/NSF Vera Rubin Observatory (Rubin),
NASA/ESA's Euclid, and NASA's Wide Field Infrared Survey Telescope (WFIRST).
The Co-Chairs of TACS, Katrin Heitmann and Alina Kiessling, invited community
scientists from the USA and Europe who are each subject matter experts and are
also members of one or more of the surveys to contribute. The following report
represents the input from TACS that was delivered to the Agencies in December
2018.Comment: 36 pages, 3 figures. Delivered to NASA, NSF, and DOE in Dec 201
Gravitational recoil: effects on massive black hole occupation fraction over cosmic time
We assess the influence of massive black hole (MBH) ejections from galaxy
centres, due to the gravitational radiation recoil, along the cosmic merger
history of the MBH population. We discuss the 'danger' of the recoil for MBHs
as a function of different MBH spin/orbit configurations and of the host halo
cosmic bias, and on how that reflects on the 'occupation fraction' of MBHs. We
assess ejection probabilities for mergers occurring in a gas-poor environment,
where the MBH binary coalescence is driven by stellar dynamical processes, and
the spin/orbit configuration is expected to be isotropically distributed. We
contrast this case with the 'aligned' case. The latter is the most realistic
situation for 'wet', gas-rich mergers, which are the expectation for
high-redshift galaxies. We find that if all halos at z>5-7 host a MBH, the
probability of the Milky Way (or similar size galaxy) to host a MBH today is
less than 50%, unless MBHs form continuously in galaxies. The 'occupation
fraction' of MBHs, intimately related to halo bias and MBH formation
efficiency, plays a crucial role in increasing the retention fraction. Small
halos, with shallow potential wells and low escape velocities, have a high
ejection probability, but the MBH merger rate is very low along their galaxy
formation merger hierarchy: MBH formation processes are likely inefficient in
such shallow potential wells. Recoils can decrease the overall frequency of
MBHs in small galaxies to ~60%, while they have little effect on the frequency
of MBHs in large galaxies (at most a 20% effect).Comment: Accepted for publication in MNRA
Semi-Analytic Modelling of Galaxy Formation: The Local Universe
Using semi-analytic models of galaxy formation, we investigate galaxy
properties such as the Tully-Fisher relation, the B and K-band luminosity
functions, cold gas contents, sizes, metallicities, and colours, and compare
our results with observations of local galaxies. We investigate several
different recipes for star formation and supernova feedback, including choices
that are similar to the treatment in Kauffmann, White & Guiderdoni (1993) and
Cole et al. (1994) as well as some new recipes. We obtain good agreement with
all of the key local observations mentioned above. In particular, in our best
models, we simultaneously produce good agreement with both the observed B and
K-band luminosity functions and the I-band Tully-Fisher relation. Improved
cooling and supernova feedback modelling, inclusion of dust extinction, and an
improved Press-Schechter model all contribute to this success. We present
results for several variants of the CDM family of cosmologies, and find that
models with values of --0.5 give the best agreement with
observations.Comment: 26 pages, LaTeX, MNRAS format, 23 inlined postscript figures.
Accepted for publication in MNRAS. Revised version contains substantial
changes including improved models. High resolution figures, original version,
and summary of changes may be found at
http://www.fiz.huji.ac.il/~rachels/papers/sp.htm
The GalMer database: Galaxy Mergers in the Virtual Observatory
We present the GalMer database, a library of galaxy merger simulations, made
available to users through tools compatible with the Virtual Observatory (VO)
standards adapted specially for this theoretical database. To investigate the
physics of galaxy formation through hierarchical merging, it is necessary to
simulate galaxy interactions varying a large number of parameters:
morphological types, mass ratios, orbital configurations, etc. On one side,
these simulations have to be run in a cosmological context, able to provide a
large number of galaxy pairs, with boundary conditions given by the large-scale
simulations, on the other side the resolution has to be high enough at galaxy
scales, to provide realistic physics. The GalMer database is a library of
thousands simulations of galaxy mergers at moderate spatial resolution and it
is a compromise between the diversity of initial conditions and the details of
underlying physics. We provide all coordinates and data of simulated particles
in FITS binary tables. The main advantages of the database are VO access
interfaces and value-added services which allow users to compare the results of
the simulations directly to observations: stellar population modelling, dust
extinction, spectra, images, visualisation using dedicated VO tools. The GalMer
value-added services can be used as virtual telescope producing broadband
images, 1D spectra, 3D spectral datacubes, thus making our database oriented
towards the usage by observers. We present several examples of the GalMer
database scientific usage obtained from the analysis of simulations and
modelling their stellar population properties, including: (1) studies of the
star formation efficiency in interactions; (2) creation of old counter-rotating
components; (3) reshaping metallicity profiles in elliptical galaxies; (4)
orbital to internal angular momentum transfer; (5) reproducing observed colour
bimodality of galaxies.Comment: 15 pages, 11 figures, 10 tables accepted to A&A. Visualisation of
GalMer simulations, access to snapshot files and value-added tools described
in the paper are available at http://galmer.obspm.fr
A deep learning approach to halo merger tree construction
A key ingredient for semi-analytic models of galaxy formation is the mass assembly history of haloes, encoded in a tree structure. The most commonly used method to construct halo merger histories is based on the outcomes of high-resolution, computationally intensive N-body simulations. We show that machine learning (ML) techniques, in particular Generative Adversarial Networks (GANs), are a promising new tool to tackle this problem with a modest computational cost and retaining the best features of merger trees from simulations. We train our GAN model with a limited sample of merger trees from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulation suite, constructed using two halo finders-tree builder algorithms: SUBFIND-D-TREES and ROCKSTAR-ConsistentTrees. Our GAN model successfully learns to generate well-constructed merger tree structures with high temporal resolution, and to reproduce the statistical features of the sample of merger trees used for training, when considering up to three variables in the training process. These inputs, whose representations are also learned by our GAN model, are mass of the halo progenitors and the final descendant, progenitor type (main halo or satellite), and distance of a progenitor to that in the main branch. The inclusion of the latter two inputs greatly improves the final learned representation of the halo mass growth history, especially for SUBFIND-like ML trees. When comparing equally sized samples of ML merger trees with those of the EAGLE simulation, we find better agreement for SUBFIND-like ML trees. Finally, our GAN-based framework can be utilized to construct merger histories of low-and intermediate-mass haloes, the most abundant in cosmological simulations.Fil: Robles, Sandra. Universidad Autónoma de Madrid; España. Kings College London (kcl); . University of Melbourne; AustraliaFil: Gómez, Jonathan S. Universidad Católica de Chile; Chile. Universidad Autónoma de Madrid; España. Pontificia Universidad Católica de Chile; ChileFil: Ramírez Rivera, Adín. University of Oslo; NoruegaFil: Padilla, Nelson David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Dujovne, Diego. Universidad Diego Portales; Chil
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