908 research outputs found
Contributions to the Power Spectrum of Cosmic Microwave Background from Fluctuations Caused by Clusters of Galaxies
We estimate the contributions to the cosmic microwave background radiation
(CMBR) power spectrum from the static and kinematic Sunyaev-Zel'dovich (SZ)
effects, and from the moving cluster of galaxies (MCG) effect. We conclude, in
agreement with other studies, that at sufficiently small scales secondary
fluctuations caused by clusters provide important contributions to the CMBR. At
, these secondary fluctuations become important relative to
lensed primordial fluctuations. Gravitational lensing at small angular scales
has been proposed as a way to break the ``geometric degeneracy'' in determining
fundamental cosmological parameters. We show that this method requires the
separation of the static SZ effect, but the kinematic SZ effect and the MCG
effect are less important. The power spectrum of secondary fluctuations caused
by clusters of galaxies, if separated from the spectrum of lensed primordial
fluctuations, might provide an independent constraint on several important
cosmological parameters.Comment: LateX, 41 pages and 10 figures. Accepted for publication in the
Astrophysical Journa
Two superluminous supernovae from the early universe discovered by the Supernova Legacy Survey
We present spectra and lightcurves of SNLS 06D4eu and SNLS 07D2bv, two
hydrogen-free superluminous supernovae discovered by the Supernova Legacy
Survey. At z = 1.588, SNLS 06D4eu is the highest redshift superluminous SN with
a spectrum, at M_U = -22.7 is one of the most luminous SNe ever observed, and
gives a rare glimpse into the restframe ultraviolet where these supernovae put
out their peak energy. SNLS 07D2bv does not have a host galaxy redshift, but
based on the supernova spectrum, we estimate it to be at z ~ 1.5. Both
supernovae have similar observer-frame griz lightcurves, which map to restframe
lightcurves in the U-band and UV, rising in ~ 20 restframe days or longer, and
declining over a similar timescale. The lightcurves peak in the shortest
wavelengths first, consistent with an expanding blackbody starting near 15,000
K and steadily declining in temperature. We compare the spectra to theoretical
models, and identify lines of C II, C III, Fe III, and Mg II in the spectrum of
SNLS 06D4eu and SCP 06F6, and find that they are consistent with an expanding
explosion of only a few solar masses of carbon, oxygen, and other trace metals.
Thus the progenitors appear to be related to those suspected for SNe Ic. A high
kinetic energy, 10^52 ergs, is also favored. Normal mechanisms of powering
core- collapse or thermonuclear supernovae do not seem to work for these
supernovae. We consider models powered by 56Ni decay and interaction with
circumstellar material, but find that the creation and spin-down of a magnetar
with a period of 2ms, magnetic field of 2 x 10^14 Gauss, and a 3 solar mass
progenitor provides the best fit to the data.Comment: ApJ, accepted, 43 pages, 15 figure
Density Variations in the NW Star Stream of M31
The Pan Andromeda Archeological Survey (PAndAS) CFHT Megaprime survey of the
M31-M33 system has found a star stream which extends about 120 kpc NW from the
center of M31. The great length of the stream, and the likelihood that it does
not significantly intersect the disk of M31, means that it is unusually well
suited for a measurement of stream gaps and clumps along its length as a test
for the predicted thousands of dark matter sub-halos. The main result of this
paper is that the density of the stream varies between zero and about three
times the mean along its length on scales of 2 to 20 kpc. The probability that
the variations are random fluctuations in the star density is less than 10^-5.
As a control sample we search for density variations at precisely the same
location in stars with metallicity higher than the stream, [Fe/H]=[0, -0.5] and
find no variations above the expected shot noise. The lumpiness of the stream
is not compatible with a low mass star stream in a smooth galactic potential,
nor is it readily compatible with the disturbance caused by the visible M31
satellite galaxies. The stream's density variations appear to be consistent
with the effects of a large population of steep mass function dark matter
sub-halos, such as found in LCDM simulations, acting on an approximately 10Gyr
old star stream. The effects of a single set of halo substructure realizations
are shown for illustration, reserving a statistical comparison for another
study.Comment: ApJ revised version submitte
Evolution and Nucleosynthesis of Zero Metal Intermediate Mass Stars
New stellar models with mass ranging between 4 and 8 Mo, Z=0 and Y=0.23 are
presented. The models have been evolved from the pre Main Sequence up to the
Asymptotic Giant Branch (AGB). At variance with previous claims, we find that
these updated stellar models do experience thermal pulses in the AGB phase. In
particular we show that: a) in models with mass larger than 6 Mo, the second
dredge up is able to raise the CNO abundance in the envelope enough to allow a
"normal" AGB evolution, in the sense that the thermal pulses and the third
dredge up settle on; b) in models of lower mass, the efficiency of the CNO
cycle in the H-burning shell is controlled by the carbon produced locally via
the 3alpha reactions. Nevertheless the He-burning shell becomes thermally
unstable after the early AGB. The expansion of the overlying layers induced by
these weak He-shell flashes is not sufficient by itself to allow a deep
penetration of the convective envelope. However, immediately after that, the
maximum luminosity of the He flash is attained and a convective shell
systematically forms at the base of the H-rich envelope. The innermost part of
this convective shell probably overlaps the underlying C-rich region left by
the inter-shell convection during the thermal pulse, so that fresh carbon is
dredged up in a "hot" H-rich environment and a H flash occurs. This flash
favours the expansion of the outermost layers already started by the weak
thermal pulse and a deeper penetration of the convective envelope takes place.
Then, the carbon abundance in the envelope rises to a level high enough that
the further evolution of these models closely resembles that of more metal rich
AGB stars. These stars provide an important source of primary carbon and
nitrogen.Comment: 28 pages, 5 tables and 17 figures. Accepted for publication in Ap
Real-time Analysis and Selection Biases in the Supernova Legacy Survey
The Supernova Legacy Survey (SNLS) has produced a high-quality, homogeneous
sample of Type Ia supernovae (SNe Ia) out to redshifts greater than z=1. In its
first four years of full operation (to June 2007), the SNLS discovered more
than 3000 transient candidates, 373 of which have been confirmed
spectroscopically as SNe Ia. Use of these SNe Ia in precision cosmology
critically depends on an analysis of the observational biases incurred in the
SNLS survey due to the incomplete sampling of the underlying SN Ia population.
This paper describes our real-time supernova detection and analysis procedures,
and uses detailed Monte Carlo simulations to examine the effects of Malmquist
bias and spectroscopic sampling. Such sampling effects are found to become
apparent at z~0.6, with a significant shift in the average magnitude of the
spectroscopically confirmed SN Ia sample towards brighter values for z>0.75. We
describe our approach to correct for these selection biases in our three-year
SNLS cosmological analysis (SNLS3), and present a breakdown of the systematic
uncertainties involved.Comment: Accepted for publication in A
SiFTO: An Empirical Method for Fitting SNe Ia Light Curves
We present SiFTO, a new empirical method for modeling type Ia supernovae (SNe
Ia) light curves by manipulating a spectral template. We make use of
high-redshift SN observations when training the model, allowing us to extend it
bluer than rest frame U. This increases the utility of our high-redshift SN
observations by allowing us to use more of the available data. We find that
when the shape of the light curve is described using a stretch prescription,
applying the same stretch at all wavelengths is not an adequate description.
SiFTO therefore uses a generalization of stretch which applies different
stretch factors as a function of both the wavelength of the observed filter and
the stretch in the rest-frame B band. We compare SiFTO to other published
light-curve models by applying them to the same set of SN photometry, and
demonstrate that SiFTO and SALT2 perform better than the alternatives when
judged by the scatter around the best fit luminosity distance relationship. We
further demonstrate that when SiFTO and SALT2 are trained on the same data set
the cosmological results agree.Comment: Modified to better match published version in Ap
SN 2016jhj at redshift 0.34: extending the Type II supernova Hubble diagram using the standard candle method
Although Type Ia supernova cosmology has now reached a mature state, it is important to develop as many independent methods as possible to understand the true nature of dark energy. Recent studies have shown that Type II supernovae (SNe II) offer such a path and could be used as alternative distance indicators. However, the majority of these studies were unable to extend the Hubble diagram above redshift z = 0.3 because of observational limitations. Here, we show that we are now ready to move beyond low redshifts and attempt high-redshift (z ≳ 0.3) SN II cosmology as a result of new-generation deep surveys such as the Subaru/Hyper Suprime-Cam survey. Applying the ´standard candle method´ to SN 2016jhj (z = 0.3398 ± 0.0002; discovered by HSC) together with a low-redshift sample, we are able to construct the highest-redshift SN II Hubble diagram to date with an observed dispersion of 0.27 mag (i.e. 12-13 per cent in distance). This work demonstrates the bright future of SN II cosmology in the coming era of large, wide-field surveys like that of the Large Synoptic Survey Telescope.Fil: de Jaeger, T.. University of California at Berkeley; Estados UnidosFil: Galbany, L.. University of Pittsburgh at Johnstown; Estados UnidosFil: Filippenko, A. V.. University of California at Berkeley; Estados UnidosFil: González Gaitán, S.. Universidad de Chile; ChileFil: Yasuda, N.. University of Tokio; JapónFil: Maeda, K.. University of Tokio; JapónFil: Tanaka, M.. University of Tokio; JapónFil: Morokuma, T.. University of Tokio; JapónFil: Moriya, T. J.. National Astronomical Observatory of Japan; JapónFil: Tominaga, N.. University of Tokyo; JapónFil: Nomoto, Ken’ichi. University of Tokyo; JapónFil: Komiyama, Y.. National Astronomical Observatory of Japan; JapónFil: Anderson, J. P.. European Southern Observatory; ChileFil: Brink, T. G.. University of California at Berkeley; Estados UnidosFil: Carlberg, R. G.. University of Toronto; CanadáFil: Folatelli, Gaston. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. University of Tokyo; JapónFil: Hamuy, M.. Universidad de Chile; ChileFil: Pignata, G.. Universidad Andrés Bello; ChileFil: Zheng, W.. University of California at Berkeley; Estados Unido
Gemini Spectroscopy of Supernovae from SNLS: Improving High Redshift SN Selection and Classification
We present new techiques for improving the efficiency of supernova (SN)
classification at high redshift using 64 candidates observed at Gemini North
and South during the first year of the Supernova Legacy Survey (SNLS). The SNLS
is an ongoing five year project with the goal of measuring the equation of
state of Dark Energy by discovering and following over 700 high-redshift SNe Ia
using data from the Canada-France-Hawaii Telescope Legacy Survey. We achieve an
improvement in the SN Ia spectroscopic confirmation rate: at Gemini 71% of
candidates are now confirmed as SNe Ia, compared to 54% using the methods of
previous surveys. This is despite the comparatively high redshift of this
sample, where the median SN Ia redshift is z=0.81 (0.155 <= z <= 1.01). These
improvements were realized because we use the unprecedented color coverage and
lightcurve sampling of the SNLS to predict whether a candidate is an SN Ia and
estimate its redshift, before obtaining a spectrum, using a new technique
called the "SN photo-z." In addition, we have improved techniques for galaxy
subtraction and SN template chi^2 fitting, allowing us to identify candidates
even when they are only 15% as bright as the host galaxy. The largest
impediment to SN identification is found to be host galaxy contamination of the
spectrum -- when the SN was at least as bright as the underlying host galaxy
the target was identified more than 90% of the time. However, even SNe on
bright host galaxies can be easily identified in good seeing conditions. When
the image quality was better than 0.55 arcsec the candidate was identified 88%
of the time. Over the five-year course of the survey, using the selection
techniques presented here we will be able to add approximately 170 more
confirmed SNe Ia than would be possible using previous methods.Comment: ApJ, accepted, 19 pages, 9 figure
Non-BBN Constraints On The Key Cosmological Parameters
Since the baryon-to-photon ratio "eta" is in some doubt at present, we ignore
the constraints on eta from big bang nucleosynthesis (BBN) and fit the three
key cosmological parameters (h, Omega_M, eta) to four other observational
constraints: Hubble parameter, age of the universe, cluster gas (baryon)
fraction, and effective shape parameter "Gamma". We consider open and flat CDM
models and flat "Lambda"-CDM models, testing goodness of fit and drawing
confidence regions by the Delta-chi^2 method. CDM models with Omega_M = 1 (SCDM
models) are accepted only because we allow a large error on h, permitting h <
0.5. Open CDM models are accepted only for Omega_M \gsim 0.4. Lambda-CDM models
give similar results. In all of these models, large eta (\gsim 6) is favored
strongly over small eta, supporting reports of low deuterium abundances on some
QSO lines of sight, and suggesting that observational determinations of
primordial 4He may be contaminated by systematic errors. Only if we drop the
crucial Gamma constraint are much lower values of Omega_M and eta permitted.Comment: 12 pages, Kluwer Latex, 2 Postscript figures, to appear in the
proceedings of the ISSI Workshop, "The Primordial Nuclei and Their Galactic
Evolution" (Bern, May 6-10, 1997), ed. N. Prantzos, M. Tosi, and R. von
Steiger (Kluwer, Dordrecht
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