The Experts below are selected from a list of 27684 Experts worldwide ranked by ideXlab platform
Alexander Rawlings - One of the best experts on this subject based on the ideXlab platform.
-
the sami galaxy survey rules of behaviour for spin Ellipticity radial tracks in galaxies
2020Co-Authors: Alexander Rawlings, Caroline Foster, Jesse Van De Sande, Dan S Taranu, S M Croom, Joss Blandhawthorn, Sarah Brough, Julia J BryantAbstract:We study the behaviour of the spin-Ellipticity radial tracks for 507 galaxies from the Sydney AAO Multiobject Integral Field (SAMI) Galaxy Survey with stellar kinematics out to ≥1.5Re. We advocate for a morpho-dynamical classification of galaxies, relying on spatially resolved photometric and kinematic data. We find the use of spin-Ellipticity radial tracks is valuable in identifying substructures within a galaxy, including embedded and counter-rotating discs, that are easily missed in unilateral studies of the photometry alone. Conversely, bars are rarely apparent in the stellar kinematics but are readily identified on images. Consequently, we distinguish the spin-Ellipticity radial tracks of seven morpho-dynamical types: elliptical, lenticular, early spiral, late spiral, barred spiral, embedded disc, and 2σ galaxies. The importance of probing beyond the inner radii of galaxies is highlighted by the characteristics of galactic features in the spin-Ellipticity radial tracks present at larger radii. The density of information presented through spin-Ellipticity radial tracks emphasizes a clear advantage to representing galaxies as a track, rather than a single point, in spin-Ellipticity parameter space.
Toshifumi Futamase - One of the best experts on this subject based on the ideXlab platform.
-
a new weak lensing shear analysis method using Ellipticity defined by 0th order moments
2015Co-Authors: Yuki Okura, Toshifumi FutamaseAbstract:We developed a new method that uses Ellipticity defined by 0th order moments (0th-Ellipticity) for weak gravitational lensing shear analysis. Although there is a strong correlation between the Ellipticity calculated using this approach and the usual Ellipticity defined by the 2nd order moment, the Ellipticity calculated here has a higher signal-to-noise ratio because it is weighted to the central region of the image. These results were confirmed using data for Abell 1689 from the Subaru telescope. For shear analysis, we adopted the Ellipticity of re-smeared artificial image method for point spread function correction, and we tested the precision of this 0th-Ellipticity with simple simulation, then we obtained the same level of precision with the results of Ellipticity defined by quadrupole moments. Thus, we can expect that weak lensing analysis using 0 shear will be improved in proportion to the statistical error.
-
a new weak lensing shear analysis method using Ellipticity defined by 0th order moments
2014Co-Authors: Yuki Okura, Toshifumi FutamaseAbstract:We developed a new method that uses Ellipticity defined by 0th order moments (0th-Ellipticity) for weak gravitational lensing shear analysis. Although there is a strong correlation between the Ellipticity calculated using this approach and the usual Ellipticity defined by the 2nd order moment, the Ellipticity calculated here has a higher signal-to-noise ratio because it is weighted to the central region of the image. These results were confirmed using data for Abell 1689 from the Subaru telescope. For shear analysis, we adopted the Ellipticity of re-smeared artificial image (ERA) method for point spread function (PSF) correction, and we tested the precision of this 0th-Ellipticity with simple simulation, then we obtained the same level of precision with the results of Ellipticity defined by quadrupole moments. Thus, we can expect that weak lensing analysis using 0 shear will be improved in proportion to the statistical error.
Massimo Viola - One of the best experts on this subject based on the ideXlab platform.
-
on the probability distributions of Ellipticity
2014Co-Authors: Massimo Viola, Thomas D Kitching, Benjamin JoachimiAbstract:In this paper we derive an exact full expression for the 2D probability distribution of the Ellipticity of an object measured from data, only assuming Gaussian noise in pixel values. This is a generalisation of the probability distribution for the ratio of single random variables, that is well-known, to the multivariate case. This expression is derived within the context of the measurement of weak gravitational lensing from noisy galaxy images. We find that the third flattening, or epsilon-Ellipticity, has a biased maximum likelihood but an unbiased mean; and that the third eccentricity, or normalised polarisation chi, has both a biased maximum likelihood and a biased mean. The very fact that the bias in the Ellipticity is itself a function of the Ellipticity requires an accurate knowledge of the intrinsic Ellipticity distribution of the galaxies in order to properly calibrate shear measurements. We use this expression to explore strategies for calibration of biases caused by measurement processes in weak gravitational lensing. We find that upcoming weak lensing surveys like KiDS or DES require calibration fields of order of several square degrees and 1.2 magnitude deeper than the wide survey in order to correct for the noise bias. Future surveys like Euclid will require calibration fields of order 40 square degree and several magnitude deeper than the wide survey. We also investigate the use of the Stokes parameters to estimate the shear as an alternative to the Ellipticity. We find that they can provide unbiased shear estimates at the cost of a very large variance in the measurement. The python code used to compute the distributions presented in the paper and to perform the numerical calculations are available on request.
-
means of confusion how pixel noise affects shear estimates for weak gravitational lensing
2012Co-Authors: P Melchior, Massimo ViolaAbstract:Weak-lensing shear estimates show a troublesome dependence on the apparent brightness of the galaxies used to measure the Ellipticity: in several studies, the amplitude of the inferred shear falls sharply with decreasing source significance. This dependence limits the overall ability of upcoming large weak-lensing surveys to constrain cosmological parameters. We seek to provide a concise overview of the impact of pixel noise on weak-lensing measurements, covering the entire path from noisy images to shear estimates. We show that there are at least three distinct layers, where pixel noise not only obscures but also biases the outcome of the measurements: (1) the propagation of pixel noise to the non-linear observable Ellipticity; (2) the response of the shape-measurement methods to limited amount of information extractable from noisy images and (3) the reaction of shear estimation statistics to the presence of noise and outliers in the measured ellipticities. We identify and discuss several fundamental problems and show that each of them is able to introduce biases in the range of a few tens to a few per cent for galaxies with typical significance levels. Furthermore, all of these biases do not only depend on the brightness of galaxies but also depend on their Ellipticity, with more elliptical galaxies often being harder to measure correctly. We also discuss existing possibilities to mitigate and novel ideas to avoid the biases induced by pixel noise. We present a new shear estimator that shows a more robust performance for noisy Ellipticity samples. Finally, we release the open-source python code to predict and efficiently sample from the noisy Ellipticity distribution and the shear estimators used in this work at https://github.com/pmelchior/epsnoise.
-
means of confusion how pixel noise affects shear estimates for weak gravitational lensing
2012Co-Authors: P Melchior, Massimo ViolaAbstract:Weak-lensing shear estimates show a troublesome dependence on the apparent brightness of the galaxies used to measure the Ellipticity: In several studies, the amplitude of the inferred shear falls sharply with decreasing source significance. This dependence limits the overall ability of upcoming large weak-lensing surveys to constrain cosmological parameters. We seek to provide a concise overview of the impact of pixel noise on weak-lensing measurements, covering the entire path from noisy images to shear estimates. We show that there are at least three distinct layers, where pixel noise not only obscures but biases the outcome of the measurements: 1) the propagation of pixel noise to the non-linear observable Ellipticity; 2) the response of the shape-measurement methods to limited amount of information extractable from noisy images; and 3) the reaction of shear estimation statistics to the presence of noise and outliers in the measured ellipticities. We identify and discuss several fundamental problems and show that each of them is able to introduce biases in the range of a few tenths to a few percent for galaxies with typical significance levels. Furthermore, all of these biases do not only depend on the brightness of galaxies but also on their Ellipticity, with more elliptical galaxies often being harder to measure correctly. We also discuss existing possibilities to mitigate and novel ideas to avoid the biases induced by pixel noise. We present a new shear estimator that shows a more robust performance for noisy Ellipticity samples. Finally, we release the open-source python code to predict and efficiently sample from the noisy Ellipticity distribution and the shear estimators used in this work at this https URL
Y P Jing - One of the best experts on this subject based on the ideXlab platform.
-
intrinsic correlation of halo Ellipticity and its implications for large scale weak lensing surveys
2002Co-Authors: Y P JingAbstract:We use a large set of state-of-the-art cosmological N-body simulations [512(3) particles] to study the intrinsic Ellipticity correlation functions of haloes. With the simulations of different resolutions, we find that the Ellipticity correlations converge once the haloes have more than 160 members. For haloes with fewer members, the correlations are underestimated, and the underestimation amounts to a factor of 2 when the haloes have only 20 particles. After correcting for the resolution effects, we show that the Ellipticity correlations of haloes in the bigger box L = 300 h(-1) Mpc) agree very well with those obtained in the smaller box (L = 100 h(-1) Mpc). Combining these results from the different simulation boxes, we present accurate fitting formulae for the Ellipticity correlation function c(11)(r) and for the projected correlation functions Sigma(11)(r(p)) and Sigma(22) (r(p)) over three orders of magnitude in halo mass. The latter two functions are useful for predicting the contribution of the intrinsic correlations to deep lensing surveys. With reasonable assumptions for the redshift distribution of galaxies and for the mass of galaxies, we find that the intrinsic Ellipticity correlation can contribute significantly not only to shallow surveys but also to deep surveys. Our results indicate that previous similar studies significantly underestimated this contribution for their limited simulation resolutions.
-
intrinsic correlation of halo Ellipticity and its implications for large scale weak lensing surveys
2002Co-Authors: Y P JingAbstract:We use a large set of state-of-the-art cosmological N-body simulations [512^3 particles] to study the intrinsic Ellipticity correlation functions of halos. With the simulations of different resolutions, we find that the Ellipticity correlations converge once the halos have more than 160 members. For halos with fewer members, the correlations are underestimated, and the underestimation amounts to a factor of 2 when the halos have only 20 particles. After correcting for the resolution effects, we show that the Ellipticity correlations of halos in the bigger box (L=300 mpc) agree very well with those obtained in the smaller box (L=100 mpc). Combining these results from the different simulation boxes, we present accurate fitting formulae for the Ellipticity correlation function c_{11}(r) and for the projected correlation functions Sigma_{11}(r_p) and Sigma_{22}(r_p) over three orders of magnitude in halo mass. The latter two functions are useful for predicting the contribution of the intrinsic correlations to deep lensing surveys. With reasonable assumptions for the redshift distribution of galaxies and for the mass of galaxies, we find that the intrinsic Ellipticity correlation can contribute significantly not only to shallow surveys but also to deep surveys. Our results indicate that previous similar studies significantly underestimated this contribution for their limited simulation resolutions.
Julia J Bryant - One of the best experts on this subject based on the ideXlab platform.
-
the sami galaxy survey rules of behaviour for spin Ellipticity radial tracks in galaxies
2020Co-Authors: Alexander Rawlings, Caroline Foster, Jesse Van De Sande, Dan S Taranu, S M Croom, Joss Blandhawthorn, Sarah Brough, Julia J BryantAbstract:We study the behaviour of the spin-Ellipticity radial tracks for 507 galaxies from the Sydney AAO Multiobject Integral Field (SAMI) Galaxy Survey with stellar kinematics out to ≥1.5Re. We advocate for a morpho-dynamical classification of galaxies, relying on spatially resolved photometric and kinematic data. We find the use of spin-Ellipticity radial tracks is valuable in identifying substructures within a galaxy, including embedded and counter-rotating discs, that are easily missed in unilateral studies of the photometry alone. Conversely, bars are rarely apparent in the stellar kinematics but are readily identified on images. Consequently, we distinguish the spin-Ellipticity radial tracks of seven morpho-dynamical types: elliptical, lenticular, early spiral, late spiral, barred spiral, embedded disc, and 2σ galaxies. The importance of probing beyond the inner radii of galaxies is highlighted by the characteristics of galactic features in the spin-Ellipticity radial tracks present at larger radii. The density of information presented through spin-Ellipticity radial tracks emphasizes a clear advantage to representing galaxies as a track, rather than a single point, in spin-Ellipticity parameter space.
