665 research outputs found
A High-Fidelity Realization of the Euclid Code Comparison -body Simulation with Abacus
We present a high-fidelity realization of the cosmological -body
simulation from the Schneider et al. (2016) code comparison project. The
simulation was performed with our Abacus -body code, which offers high force
accuracy, high performance, and minimal particle integration errors. The
simulation consists of particles in a box,
for a particle mass of with $10\
h^{-1}\mathrm{kpc}z=0<0.3\%k<10\
\mathrm{Mpc}^{-1}h0.01\%$. Simulation snapshots are available at
http://nbody.rc.fas.harvard.edu/public/S2016 .Comment: 13 pages, 8 figures. Minor changes to match MNRAS accepted versio
Type II Supernovae as Standardized Candles
We present evidence for a correlation between expansion velocities of the
ejecta of Type II plateau supernovae and their bolometric luminosities during
the plateau phase. This correlation permits one to standardize the candles and
decrease the scatter in the Hubble diagram from ~1 mag to a level of 0.4 and
0.3 mag in the V and I bands, respectively. When we restrict the sample to the
eight objects which are well in the Hubble flow (cz > 3,000 km/s) the scatter
drops even further to only 0.2 mag (or 9% in distance), which is comparable to
the precision yielded by Type Ia supernovae and far better than the ``expanding
photosphere method'' applied to Type II supernovae. Using SN 1987A to calibrate
the Hubble diagrams we get Ho=55+/-12.Comment: 9 pages, 3 figures, 1 table, accepted by ApJ
Measuring Baryon Acoustic Oscillations with Millions of Supernovae
Since type Ia Supernovae (SNe) explode in galaxies, they can, in principle,
be used as the same tracer of the large-scale structure as their hosts to
measure baryon acoustic oscillations (BAOs). To realize this, one must obtain a
dense integrated sampling of SNe over a large fraction of the sky, which may
only be achievable photometrically with future projects such as the Large
Synoptic Survey Telescope. The advantage of SN BAOs is that SNe have more
uniform luminosities and more accurate photometric redshifts than galaxies, but
the disadvantage is that they are transitory and hard to obtain in large number
at high redshift. We find that a half-sky photometric SN survey to redshift z =
0.8 is able to measure the baryon signature in the SN spatial power spectrum.
Although dark energy constraints from SN BAOs are weak, they can significantly
improve the results from SN luminosity distances of the same data, and the
combination of the two is no longer sensitive to cosmic microwave background
priors.Comment: 4 pages, 3 figures, ApJL accepte
Selection Effects, Biases, and Constraints in the Calan/Tololo Supernova Survey
We use Monte Carlo simulations of the Calan/Tololo photographic supernova
survey to show that a simple model of the survey's selection effects accounts
for the observed distributions of recession velocity, apparent magnitude,
angular offset, and projected radial distance between the supernova and the
host galaxy nucleus for this sample of Type Ia supernovae (SNe Ia). The model
includes biases due to the flux-limited nature of the survey, the different
light curve morphologies displayed by different SNe Ia, and the difficulty of
finding events projected near the central regions of the host galaxies. From
these simulations we estimate the bias in the zero-point and slope of the
absolute magnitude-decline rate relation used in SNe Ia distance measurements.
For an assumed intrinsic scatter of 0.15 mag about this relation, these
selection effects decrease the zero-point by 0.04 mag. The slope of the
relation is not significantly biased. We conclude that despite selection
effects in the survey, the shape and zero-point of the relation determined from
the Calan/Tololo sample are quite reliable. We estimate the degree of
incompleteness of the survey as a function of decline rate and estimate a
corrected luminosity function for SNe Ia in which the frequency of SNe appears
to increase with decline rate (the fainter SNe are more common). Finally, we
compute the integrated detection efficiency of the survey in order to infer the
rate of SNe Ia from the 31 events found. For a value of Ho=65 km/sec/Mpc we
obtain a SN Ia rate of 0.21(+0.30)(-0.13) SNu. This is in good agreement with
the value 0.16+/-0.05 SNu recently determined by Capellaro et al. (1997).Comment: 36 pages, 19 figures as extra files, to appear in the A
Iron Opacity and the Pulsar of Supernova 1987A
Neutron stars formed in Type II supernovae are likely to be initially
obscured by late-time fallback. Although much of the late-time fallback is
quickly accreted via neutrino cooling, some material remains on the neutron
star, forming an atmosphere which slowly accretes through photon emission. In
this paper, we derive structure equations of the fallback atmosphere and
present results of one-dimensional simulations of that fallback. The atmosphere
remaining after neutrino cooling becomes unimportant (less than the Compton
Eddington limit) is only a fraction of the total mass accreted (10^-8 of the
accreted mass or 10^-9 solar masses.) Recombined iron dominates the opacity in
the outer regions leading to an opacity 1000-10,000 times higher than that of
electron scattering alone. The resultant photon emission of the remnant
atmosphere is limited to 1/1000th the Compton Eddington Luminosity. The
late-time evolution of this system leads to the formation of a photon-driven
wind from the accretion of the inner portion of the atmosphere, leaving, for
most cases, a bare neutron star on timescales shorter than a year. The
degenerate remnant of 1987a may not be a black hole. Instead, the fallback
material may have already accreted or blown off in the accretion-driven wind.
If the neutron star has either a low magnetic field or a low rotational spin
frequency, we would not expect to see the neutron star remnant of 1987a.Comment: 15 pages text + 8 figures, accepted by Ap
The Abacus Cosmos: A Suite of Cosmological N-body Simulations
We present a public data release of halo catalogs from a suite of 125
cosmological -body simulations from the Abacus project. The simulations span
40 CDM cosmologies centered on the Planck 2015 cosmology at two mass
resolutions, and , in and
boxes, respectively. The boxes are phase-matched to
suppress sample variance and isolate cosmology dependence. Additional volume is
available via 16 boxes of fixed cosmology and varied phase; a few boxes of
single-parameter excursions from Planck 2015 are also provided. Catalogs
spanning to are available for friends-of-friends and Rockstar
halo finders and include particle subsamples. All data products are available
at https://lgarrison.github.io/AbacusCosmosComment: 13 pages, 9 figures, 3 tables. Additional figures added for mass
resolution convergence tests, and additional redshifts added for existing
tests. Matches ApJS accepted versio
A Search for Environmental Effects on Type Ia Supernovae
We use integrated colors and B and V absolute magnitudes of Type Ia supernova
(SN) host galaxies in order to search for environmental effects on the SN
optical properties. With the new sample of 44 SNe we confirm the conclusion by
Hamuy et al. (1996a) that bright events occur preferentially in young stellar
environments. We find also that the brightest SNe occur in the least luminous
galaxies, a possible indication that metal-poorer neighbourhoods produce the
more luminous events. The interpretation of these results is made difficult,
however, due to the fact that galaxies with younger stellar populations are
also lower in luminosity. In an attempt to remove this ambiguity we use models
for the line strengths in the absorption spectrum of five early-type galaxies,
in order to estimate metallicities and ages of the SN host galaxies. With the
addition of abundance estimates from nebular analysis of the emission spectra
of three spiral galaxies, we find possible further evidence that luminous SNe
are produced in metal-poor neighborhoods. Further spectroscopic observations of
the SN host galaxies will be necessary to test these results and assist in
disentangling the age/metallicity effects on Type Ia SNe.Comment: 14 pages, 5 figures, to appear in the September 2000 issue of The
Astronomical Journa
Shock Breakout in Core-Collapse Supernovae and its Neutrino Signature
(Abridged) We present results from dynamical models of core-collapse
supernovae in one spatial dimension, employing a newly-developed Boltzmann
neutrino radiation transport algorithm, coupled to Lagrangean hydrodynamics and
a consistent high-density nuclear equation of state. We focus on shock breakout
and its neutrino signature and follow the dynamical evolution of the cores of
11 M_sun, 15 M_sun, and 20 M_sun progenitors through collapse and the first 250
milliseconds after bounce. We examine the effects on the emergent neutrino
spectra, light curves, and mix of species of artificial opacity changes, the
number of energy groups, the weak magnetism/recoil corrections, nucleon-nucleon
bremsstrahlung, neutrino-electron scattering, and the compressibility of
nuclear matter. Furthermore, we present the first high-resolution look at the
angular distribution of the neutrino radiation field both in the
semi-transparent regime and at large radii and explore the accuracy with which
our tangent-ray method tracks the free propagation of a pulse of radiation in a
near vacuum. Finally, we fold the emergent neutrino spectra with the
efficiencies and detection processes for a selection of modern underground
neutrino observatories and argue that the prompt electron-neutrino breakout
burst from the next galactic supernova is in principle observable and usefully
diagnostic of fundamental collapse/supernova behavior. Though we are not in
this study focusing on the supernova mechanism per se, our simulations support
the theoretical conclusion (already reached by others) that spherical (1D)
supernovae do not explode when good physics and transport methods are employed.Comment: 16 emulateapj pages, plus 24 postscript figures, accepted to The
Astrophysical Journal; text revised; neutrino oscillation section expanded;
Fig. 22 correcte
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