2006.16263
Plasma lensing in comparison to gravitational lensing -- Formalism and degeneracies
Wagner, Er
Gravitational and plasma lensing share the same mathematical formalism in the limit of geometrical optics. Both phenomena can be effectively described by a projected, two-dimensional deflection potential whose gradient causes an instantaneous light deflection in a single, thin lens plane. We highlight the differences in the time-delay and lensing equations that occur because plasma lensing is caused by a potential directly proportional to the deflecting electron number density and gravitational lensing is caused by a potential related to the deflecting mass density by a Poisson equation. Since we treat plasma and gravitational lensing as thin-screen effective theories, their degeneracies are both caused by the unknown distribution of deflecting objects. Deriving the formalism-intrinsic degeneracies for plasma lensing, we find that they are analogous to those occurring in gravitational lensing. To break the degeneracies, galaxies and galaxy-cluster scale strong gravitational lenses must rely on additional assumptions or complementary observations. Physically realistic assumptions to arrive at self-consistent lens and source reconstructions can be provided by simulations and analytical effective theories. In plasma lensing, a deeper understanding of the deflecting electron density distributions is still under development, so that a model-based comprehensive lens reconstruction is not yet possible. However, we show that transient lenses and multi-wavelength observations help to break the arising degeneracies. We conclude that the development of an observation-based inference of local lens properties seems currently the best way to further probe the morphologies of plasma electron densities. Due to the simpler evidence-based breaking of the lensing degeneracies, we expect to obtain tighter constraints on the local plasma electron densities than on the gravitationally deflecting masses.
2007.00386
Constraining the masses of high-redshift clusters with weak lensing: revised shape calibration testing for the impact of stronger sears and increased blending
Hernandez-Martin, Schrabback, Hoekstra, et al
WL measurements have well-known shear estimation biases, which can be partially corrected for with the use of image simulations. We present an analysis of simulated images that mimic HST/ACS observations of high-redshift galaxy clusters, including cluster specific issues such as non-weak shear and increased blending. Our synthetic galaxies have been generated to match the observed properties of the background-selected samples in the real images. First, we used simulations with galaxies on a grid to determine a revised signal-to-noise-dependent correction for multiplicative shear measurement bias, and to quantify the sensitivity of our bias calibration to mismatches of galaxy or PSF properties between the real data and the simulations. We studied the impact of increased blending and light contamination from cluster and foreground galaxies, finding it negligible for $z>0.7$ clusters, whereas there is an effect at the $\sim 1\%$ level for lower redshift clusters. Finally, we studied the impact of fainter neighbours and selection bias mimicking the positions and magnitudes of galaxies in CANDELS data. The initial SExtractor object detection causes a selection bias of $-0.028 \pm 0.002$, reduced to $-0.016 \pm 0.002$ by further cuts. We compared our CANDELS-based estimate to a grid-based analysis, with added clustered galaxies reaching even fainter magnitudes, yielding a refined estimate of $\sim -0.013$. Our pipeline is calibrated to an accuracy of $\sim 0.015$, which is fully sufficient for current and near-future weak lensing studies of high-redshift clusters. As an application, we used it for a refined analysis of three highly relaxed clusters from the SPT-SZ survey, including measurements down to $r>200$ kpc. Compared to previously employed scales, this tightens the cluster mass constraints by a factor 1.38 on average.
Plasma lensing in comparison to gravitational lensing -- Formalism and degeneracies
Wagner, Er
Gravitational and plasma lensing share the same mathematical formalism in the limit of geometrical optics. Both phenomena can be effectively described by a projected, two-dimensional deflection potential whose gradient causes an instantaneous light deflection in a single, thin lens plane. We highlight the differences in the time-delay and lensing equations that occur because plasma lensing is caused by a potential directly proportional to the deflecting electron number density and gravitational lensing is caused by a potential related to the deflecting mass density by a Poisson equation. Since we treat plasma and gravitational lensing as thin-screen effective theories, their degeneracies are both caused by the unknown distribution of deflecting objects. Deriving the formalism-intrinsic degeneracies for plasma lensing, we find that they are analogous to those occurring in gravitational lensing. To break the degeneracies, galaxies and galaxy-cluster scale strong gravitational lenses must rely on additional assumptions or complementary observations. Physically realistic assumptions to arrive at self-consistent lens and source reconstructions can be provided by simulations and analytical effective theories. In plasma lensing, a deeper understanding of the deflecting electron density distributions is still under development, so that a model-based comprehensive lens reconstruction is not yet possible. However, we show that transient lenses and multi-wavelength observations help to break the arising degeneracies. We conclude that the development of an observation-based inference of local lens properties seems currently the best way to further probe the morphologies of plasma electron densities. Due to the simpler evidence-based breaking of the lensing degeneracies, we expect to obtain tighter constraints on the local plasma electron densities than on the gravitationally deflecting masses.
2007.00386
Constraining the masses of high-redshift clusters with weak lensing: revised shape calibration testing for the impact of stronger sears and increased blending
Hernandez-Martin, Schrabback, Hoekstra, et al
WL measurements have well-known shear estimation biases, which can be partially corrected for with the use of image simulations. We present an analysis of simulated images that mimic HST/ACS observations of high-redshift galaxy clusters, including cluster specific issues such as non-weak shear and increased blending. Our synthetic galaxies have been generated to match the observed properties of the background-selected samples in the real images. First, we used simulations with galaxies on a grid to determine a revised signal-to-noise-dependent correction for multiplicative shear measurement bias, and to quantify the sensitivity of our bias calibration to mismatches of galaxy or PSF properties between the real data and the simulations. We studied the impact of increased blending and light contamination from cluster and foreground galaxies, finding it negligible for $z>0.7$ clusters, whereas there is an effect at the $\sim 1\%$ level for lower redshift clusters. Finally, we studied the impact of fainter neighbours and selection bias mimicking the positions and magnitudes of galaxies in CANDELS data. The initial SExtractor object detection causes a selection bias of $-0.028 \pm 0.002$, reduced to $-0.016 \pm 0.002$ by further cuts. We compared our CANDELS-based estimate to a grid-based analysis, with added clustered galaxies reaching even fainter magnitudes, yielding a refined estimate of $\sim -0.013$. Our pipeline is calibrated to an accuracy of $\sim 0.015$, which is fully sufficient for current and near-future weak lensing studies of high-redshift clusters. As an application, we used it for a refined analysis of three highly relaxed clusters from the SPT-SZ survey, including measurements down to $r>200$ kpc. Compared to previously employed scales, this tightens the cluster mass constraints by a factor 1.38 on average.
2007.00555
What is the price of abandoning dark matter? Cosmological constraints on alternative gravity theories
Pardo, Spergel
Any successful alternative gravity theory that obviates the need for dark matter must fit our cosmological observations. Measurements of microwave background polarization trace the large-scale baryon velocity field at recombination and show very strong, $O(1)$, baryon acoustic oscillations. Measurements of the large-scale structure of galaxies at low redshift show much weaker features in the spectrum. If the alternative gravity theory's dynamical equations for the growth rate of structure are linear, then the density field growth can be described by a Green's function: $\delta(\vec x,t) = \delta(\vec x,t')G(x,t,t')$. We show that the Green function, $G(x,t,t')$, must have dramatic features that erase the initial baryon oscillations. This implies an acceleration law that changes sign on the $\sim 150$ Mpc scale. On the other hand, if the alternative gravity theory has a large nonlinear term that couples modes on different scales, then the theory would predict large-scale non-Gaussian features in large-scale structure. These are not seen in the distribution of galaxies nor in the distribution of quasars. No proposed alternative gravity theory for dark matter seems to satisfy these constraints.
2007.00609
The surface brightness of the trails of megaconstellation's satellites on large telescopes
Ragazzoni
On large telescopes trails of MegaConstellation's satellites will appears significantly defocused because of their relatively short distance. Because of such effect their apparent surface brightness will be, under a range of conditions, almost constant during their apparent sweeping on the focal plane of such large facilities. A few simple relationships are worked out and discussed to show the apparent brightness of such trails, in order to evaluate their impact on operations of large optical ground based facilities. Such considerations could be used as well to propose regulatory limits in order to make such effects small enough.
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