112 research outputs found
3D Reconstruction of the Density Field: An SVD Approach to Weak Lensing Tomography
We present a new method for constructing three-dimensional mass maps from
gravitational lensing shear data. We solve the lensing inversion problem using
truncation of singular values (within the context of generalized least squares
estimation) without a priori assumptions about the statistical nature of the
signal. This singular value framework allows a quantitative comparison between
different filtering methods: we evaluate our method beside the previously
explored Wiener filter approaches. Our method yields near-optimal angular
resolution of the lensing reconstruction and allows cluster sized halos to be
de-blended robustly. It allows for mass reconstructions which are 2-3
orders-of-magnitude faster than the Wiener filter approach; in particular, we
estimate that an all-sky reconstruction with arcminute resolution could be
performed on a time-scale of hours. We find however that linear, non-parametric
reconstructions have a fundamental limitation in the resolution achieved in the
redshift direction.Comment: 11 pages, 6 figures. Accepted for publication in Ap
Interpolating Masked Weak Lensing Signal with Karhunen-Loeve Analysis
We explore the utility of Karhunen Loeve (KL) analysis in solving practical
problems in the analysis of gravitational shear surveys. Shear catalogs from
large-field weak lensing surveys will be subject to many systematic
limitations, notably incomplete coverage and pixel-level masking due to
foreground sources. We develop a method to use two dimensional KL eigenmodes of
shear to interpolate noisy shear measurements across masked regions. We explore
the results of this method with simulated shear catalogs, using statistics of
high-convergence regions in the resulting map. We find that the KL procedure
not only minimizes the bias due to masked regions in the field, it also reduces
spurious peak counts from shape noise by a factor of ~ 3 in the cosmologically
sensitive regime. This indicates that KL reconstructions of masked shear are
not only useful for creating robust convergence maps from masked shear
catalogs, but also offer promise of improved parameter constraints within
studies of shear peak statistics.Comment: 13 pages, 9 figures; submitted to Ap
First-Year Sloan Digital Sky Survey-II (SDSS-II) Supernova Results: Constraints on Non-Standard Cosmological Models
We use the new SNe Ia discovered by the SDSS-II Supernova Survey together
with additional supernova datasets as well as observations of the cosmic
microwave background and baryon acoustic oscillations to constrain cosmological
models. This complements the analysis presented by Kessler et al. in that we
discuss and rank a number of the most popular non-standard cosmology scenarios.
When this combined data-set is analyzed using the MLCS2k2 light-curve fitter,
we find that more exotic models for cosmic acceleration provide a better fit to
the data than the Lambda-CDM model. For example, the flat DGP model is ranked
higher by our information criteria tests than the standard model. When the
dataset is instead analyzed using the SALT-II light-curve fitter, the standard
cosmological constant model fares best. Our investigation also includes
inhomogeneous Lemaitre-Tolman-Bondi (LTB) models. While our LTB models can be
made to fit the supernova data as well as any other model, the extra parameters
they require are not supported by our information criteria analysis.Comment: ApJ in press, updated reference
Estimating Level of Engagement from Ocular Landmarks
E-learning offers many advantages like being economical, flexible and customizable, but also has challenging aspects such as lack of – social-interaction, which results in contemplation and sense of remoteness. To overcome these and sustain learners’ motivation, various stimuli can be incorporated. Nevertheless, such adjustments initially require an assessment of engagement level. In this respect, we propose estimating engagement level from facial landmarks exploiting the facts that (i) perceptual decoupling is promoted by blinking during mentally demanding tasks; (ii) eye strain increases blinking rate, which also scales with task disengagement; (iii) eye aspect ratio is in close connection with attentional state and (iv) users’ head position is correlated with their level of involvement. Building empirical models of these actions, we devise a probabilistic estimation framework. Our results indicate that high and low levels of engagement are identified with considerable accuracy, whereas medium levels are inherently more challenging, which is also confirmed by inter-rater agreement of expert coders
First-year Sloan Digital Sky Survey-II (SDSS-II) supernova results: consistency and constraints with other intermediate-redshift datasets
We present an analysis of the luminosity distances of Type Ia Supernovae from
the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey in conjunction with
other intermediate redshift (z<0.4) cosmological measurements including
redshift-space distortions from the Two-degree Field Galaxy Redshift Survey
(2dFGRS), the Integrated Sachs-Wolfe (ISW) effect seen by the SDSS, and the
latest Baryon Acoustic Oscillation (BAO) distance scale from both the SDSS and
2dFGRS. We have analysed the SDSS-II SN data alone using a variety of
"model-independent" methods and find evidence for an accelerating universe at
>97% level from this single dataset. We find good agreement between the
supernova and BAO distance measurements, both consistent with a
Lambda-dominated CDM cosmology, as demonstrated through an analysis of the
distance duality relationship between the luminosity (d_L) and angular diameter
(d_A) distance measures. We then use these data to estimate w within this
restricted redshift range (z<0.4). Our most stringent result comes from the
combination of all our intermediate-redshift data (SDSS-II SNe, BAO, ISW and
redshift-space distortions), giving w = -0.81 +0.16 -0.18(stat) +/- 0.15(sys)
and Omega_M=0.22 +0.09 -0.08 assuming a flat universe. This value of w, and
associated errors, only change slightly if curvature is allowed to vary,
consistent with constraints from the Cosmic Microwave Background. We also
consider more limited combinations of the geometrical (SN, BAO) and dynamical
(ISW, redshift-space distortions) probes.Comment: 13 pages, 7 figures, accepted for publication in MNRA
The Astropy Project: Building an Open-science Project and Status of the v2.0 Core Package
The Astropy Project supports and fosters the development of open-source and openly developed Python packages that provide commonly needed functionality to the astronomical community. A key element of the Astropy Project is the core package astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package, as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of interoperable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy Project
The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
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