9,495 research outputs found
Analytic Photometric Redshift Estimator for Type Ia Supernovae From the Large Synoptic Survey Telescope
Accurate and precise photometric redshifts (photo-z's) of Type Ia supernovae
(SNe Ia) can enable the use of SNe Ia, measured only with photometry, to probe
cosmology. This dramatically increases the science return of supernova surveys
planned for the Large Synoptic Survey Telescope (LSST). In this paper we
describe a significantly improved version of the simple analytic photo-z
estimator proposed by Wang (2007) and further developed by Wang, Narayan, and
Wood-Vasey (2007). We apply it to 55,422 simulated SNe Ia generated using the
SNANA package with the LSST filters. We find that the estimated errors on the
photo-z's, \sigma_{z_{phot}}/(1+z_{phot}), can be used as filters to produce a
set of photo-z's that have high precision, accuracy, and purity. Using SN Ia
colors as well as SN Ia peak magnitude in the i band, we obtain a set of
photo-z's with 2 percent accuracy (with \sigma(z_{phot}-z_{spec})/(1+z_{spec})
= 0.02), a bias in z_{phot} (the mean of z_{phot}-z_{spec}) of -9 X 10^{-5},
and an outlier fraction (with |(z_{phot}-z_{spec})/(1+z_{spec})|>0.1) of 0.23
percent, with the requirement that \sigma_{z_{phot}}/(1+z_{phot})<0.01. Using
the SN Ia colors only, we obtain a set of photo-z's with similar quality by
requiring that \sigma_{z_{phot}}/(1+z_{phot})<0.007; this leads to a set of
photo-z's with 2 percent accuracy, a bias in z_{phot} of 5.9 X 10^{-4}, and an
outlier fraction of 0.32 percent.Comment: 10 pages, 8 figures, 2 tables. Revised version, accepted by MNRA
Observational Bounds on Modified Gravity Models
Modified gravity provides a possible explanation for the currently observed
cosmic accelaration. In this paper, we study general classes of modified
gravity models. The Einstein-Hilbert action is modified by using general
functions of the Ricci and the Gauss-Bonnet scalars, both in the metric and in
the Palatini formalisms. We do not use an explicit form for the functions, but
a general form with a valid Taylor expansion up to second order about redshift
zero in the Riemann-scalars. The coefficients of this expansion are then
reconstructed via the cosmic expansion history measured using current
cosmological observations. These are the quantities of interest for theoretical
considerations relating to ghosts and instabilities. We find that current data
provide interesting constraints on the coefficients. The next-generation dark
energy surveys should shrink the allowed parameter space for modifed gravity
models quite dramatically.Comment: 23 pages, 5 figures, uses RevTe
Recommended from our members
Lignin-Based Polyurethanes from Unmodified Kraft Lignin Fractionated by Sequential Precipitation
Uncorrelated Measurements of the Cosmic Expansion History and Dark Energy from Supernovae
We present a method for measuring the cosmic expansion history H(z) in
uncorrelated redshift bins, and apply it to current and simulated type Ia
supernova data assuming spatial flatness. If the matter density parameter
Omega_m can be accurately measured from other data, then the dark energy
density history X(z)=rho_X(z)/rho_X(0) can trivially be derived from this
expansion history H(z). In contrast to customary ``black box'' parameter
fitting, our method is transparent and easy to interpret: the measurement of
H(z)^{-1} in a redshift bin is simply a linear combination of the measured
comoving distances for supernovae in that bin, making it obvious how systematic
errors propagate from input to output.
We find the Riess et al. (2004) ``gold'' sample to be consistent with the
``vanilla'' concordance model where the dark energy is a cosmological constant.
We compare two mission concepts for the NASA/DOE Joint Dark Energy Mission
(JDEM), the Joint Efficient Dark-energy Investigation (JEDI), and the Supernova
Accelaration Probe (SNAP), using simulated data including the effect of weak
lensing (based on numerical simulations) and a systematic bias from
K-corrections. Estimating H(z) in seven uncorrelated redshift bins, we find
that both provide dramatic improvements over current data: JEDI can measure
H(z) to about 10% accuracy and SNAP to 30-40% accuracy.Comment: 7 pages, 4 color figures. Expanded and revised version; PRD in pres
Quark mass density- and temperature- dependent model for strange quark matter
It is found that the radius of a stable strangelet decreases as the
temperature increases in a quark mass density-dependent model. To overcome this
difficulty, we extend this model to a quark mass density- and temperature-
dependent model in which the vacuum energy density at zero baryon density limit
B depends on temperature. An ansatz is introduced and the regions for the best
choice of the parameters are studied.Comment: 5 pages, 4 figure
Object Contour and Edge Detection with RefineContourNet
A ResNet-based multi-path refinement CNN is used for object contour
detection. For this task, we prioritise the effective utilization of the
high-level abstraction capability of a ResNet, which leads to state-of-the-art
results for edge detection. Keeping our focus in mind, we fuse the high, mid
and low-level features in that specific order, which differs from many other
approaches. It uses the tensor with the highest-levelled features as the
starting point to combine it layer-by-layer with features of a lower
abstraction level until it reaches the lowest level. We train this network on a
modified PASCAL VOC 2012 dataset for object contour detection and evaluate on a
refined PASCAL-val dataset reaching an excellent performance and an Optimal
Dataset Scale (ODS) of 0.752. Furthermore, by fine-training on the BSDS500
dataset we reach state-of-the-art results for edge-detection with an ODS of
0.824.Comment: Keywords: Object Contour Detection, Edge Detection, Multi-Path
Refinement CN
A CO emission line from the optical and near-IR undetected submillimeter galaxy GN10
We report the detection of a CO emission line from the submillimiter galaxy
(SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep
optical and near-IR imaging obtained with the Hubble Space Telescope and
ground-based facilities. This is a prototypical case of a source that is
extremely obscured by dust, for which it is practically impossible to derive a
spectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10
is part of a proto-cluster structure previously identified at z~4.05 in the
same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure
Interferometer, and successfully detected a line. We find that the most likely
redshift identification is z=4.0424+-0.0013, based on: 1) the very low chance
that the CO line is actually serendipitous from a different redshift; 2) a
radio-IR photometric redshift analysis; 3) the identical radio-IR SED, within a
scaling factor, of two other SMGs at the same redshift. The faintness at
optical/near-IR wavelengths requires an attenuation of A_V~5-7.5 mag. This
result supports the case that a substantial population of very high-z SMGs
exists that had been missed by previous spectroscopic surveys. This is the
first time that a CO emission line has been detected for a galaxy that is
invisible in the optical and near-IR. Our work demonstrates the power of
existing and planned facilities for completing the census of star formation and
stellar mass in the distant Universe by measuring redshifts of the most
obscured galaxies through millimeter spectroscopy.Comment: 5 pages, 4 figures. ApJ Letters in pres
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