The redshift distribution of faint galaxies — Implications for gravitational lensing

2006 ◽  
pp. 236-243 ◽  
Author(s):  
Richard S. Ellis
Keyword(s):  
Gravitational Lensing ◽  
Redshift Distribution

scholarly journals Quantized Redshifts - New Physics or Old Muddle?

1999 ◽  
Vol 194 ◽  
pp. 290-294
Author(s):  
W.M. Napier
Keyword(s):  
Energy Density ◽  
Gravitational Lensing ◽  
Confidence Level ◽  
Spiral Galaxies ◽  
New Physics ◽  
Frame Of Reference ◽  
High Confidence ◽  
Redshift Distribution ◽  
Massive Galaxies ◽  
High Confidence Level

The HI redshift distribution of nearby spiral galaxies has been studied to test long-running but generally ignored claims that extragalactic redshifts are periodic or ‘quantized’. The existence of the phenomenon is confirmed at an extremely high confidence level, the quantization appearing in the galactocentric frame of reference. It is proposed that the energy density of the vacuum is a local, oscillating quantity associated with large masses such as spiral galaxies. A variety of ‘anomalies’ should then be detectable in massive galaxies, associated with their redshifts, their ambient gravitational lensing and their dynamics.

scholarly journals Emulation of Cosmological Mass Maps with Conditional Generative Adversarial Networks

2021 ◽  
Vol 4 ◽  
Author(s):  
Nathanaël Perraudin ◽  
Sandro Marcon ◽  
Aurelien Lucchi ◽  
Tomasz Kacprzak
Keyword(s):  
Gravitational Lensing ◽  
Cosmological Parameters ◽  
Similarity Index ◽  
Power Spectra ◽  
Generative Models ◽  
Generative Adversarial Networks ◽  
Summary Statistics ◽  
Redshift Distribution ◽  
Adversarial Networks ◽  
The Universe

Weak gravitational lensing mass maps play a crucial role in understanding the evolution of structures in the Universe and our ability to constrain cosmological models. The prediction of these mass maps is based on expensive N-body simulations, which can create a computational bottleneck for cosmological analyses. Simulation-based emulators of map summary statistics, such as the matter power spectrum and its covariance, are starting to play increasingly important role, as the analytical predictions are expected to reach their precision limits for upcoming experiments. Creating an emulator of the cosmological mass maps themselves, rather than their summary statistics, is a more challenging task. Modern deep generative models, such as Generative Adversarial Networks (GAN), have demonstrated their potential to achieve this goal. Most existing GAN approaches produce simulations for a fixed value of the cosmological parameters, which limits their practical applicability. We propose a novel conditional GAN model that is able to generate mass maps for any pair of matter density Ωm and matter clustering strength σ8, parameters which have the largest impact on the evolution of structures in the Universe, for a given source galaxy redshift distribution n(z). Our results show that our conditional GAN can interpolate efficiently within the space of simulated cosmologies, and generate maps anywhere inside this space with good visual quality high statistical accuracy. We perform an extensive quantitative comparison of the N-body and GAN -generated maps using a range of metrics: the pixel histograms, peak counts, power spectra, bispectra, Minkowski functionals, correlation matrices of the power spectra, the Multi-Scale Structural Similarity Index (MS-SSIM) and our equivalent of the Fréchet Inception Distance. We find a very good agreement on these metrics, with typical differences are <5% at the center of the simulation grid, and slightly worse for cosmologies at the grid edges. The agreement for the bispectrum is slightly worse, on the <20% level. This contribution is a step toward building emulators of mass maps directly, capturing both the cosmological signal and its variability. We make the code1 and the data2 publicly available.

scholarly journals Weak Gravitational Lensing—The Need for Surveys

1998 ◽  
Vol 179 ◽  
pp. 241-248
Author(s):  
P. Schneider
Keyword(s):  
Mass Distribution ◽  
Gravitational Lensing ◽  
Compact Objects ◽  
Gravitational Lens ◽  
Weak Lensing ◽  
Wide Field ◽  
Redshift Distribution ◽  
Weak Gravitational Lensing ◽  
Distant Galaxies ◽  
Galaxy Population

Light rays from distant sources are deflected if they pass near an intervening matter inhomogeneity. This gravitational lens effect is responsible for the well-established lens systems like multiple-imaged QSOs, (radio) ‘Einstein’ rings, the giant luminous arcs in clusters of galaxies, and the flux variations of stars in the LMC and the Galactic bulge seen in the searches for compact objects in our Galaxy. These types of lensing events are nowadays called ‘strong lensing,’ to distinguish it from the effects discussed here: light bundles are not only deflected as a whole, but distorted by the tidal gravitational field of the deflector. This image distortion can be quite weak and can then not be detected in individual images. However, since we are lucky to live in a Universe where the sky is full of faint distant galaxies, this distortion effect can be discovered statistically. This immediately implies that weak lensing requires excellent and deep images so that image shapes (and sizes) can be accurately measured and the number density be as high as possible to reduce statistical uncertainties. Weak gravitational lensing can be defined as using the faint galaxy population to measure the mass and/or mass distribution of individual intervening cosmic structures, or the statistical properties of their mass distribution, or to detect them in the first place, independent of the physical state or nature of the matter, or the luminosity of these mass concentrations. In addition, weak lensing can be used to infer the redshift distribution of the faintest galaxies. After introducing the necessary concepts, I will list the main applications of weak lensing and discuss some of them in slightly more detail, stressing the need for very deep and wide-field images of the sky taken with instruments of excellent image quality.

scholarly journals Cosmological constraints from cosmic shear two-point correlation functions with HSC survey first-year data

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Takashi Hamana ◽  
Masato Shirasaki ◽  
Satoshi Miyazaki ◽  
Chiaki Hikage ◽  
Masamune Oguri ◽  
...  
Keyword(s):  
Gravitational Lensing ◽  
Correlation Functions ◽  
Cold Dark Matter ◽  
First Year ◽  
Model Errors ◽  
Redshift Distribution ◽  
Cosmological Constraints ◽  
Modeling Uncertainties ◽  
Point Correlation ◽  
Cosmic Shear

Abstract We present measurements of cosmic shear two-point correlation functions (TPCFs) from Hyper Suprime-Cam Subaru Strategic Program (HSC) first-year data, and derive cosmological constraints based on a blind analysis. The HSC first-year shape catalog is divided into four tomographic redshift bins ranging from $z=0.3$ to 1.5 with equal widths of $\Delta z =0.3$. The unweighted galaxy number densities in each tomographic bin are 5.9, 5.9, 4.3, and $2.4\:$arcmin$^{-2}$ from the lowest to highest redshifts, respectively. We adopt the standard TPCF estimators, $\xi _\pm$, for our cosmological analysis, given that we find no evidence of significant B-mode shear. The TPCFs are detected at high significance for all 10 combinations of auto- and cross-tomographic bins over a wide angular range, yielding a total signal-to-noise ratio of 19 in the angular ranges adopted in the cosmological analysis, $7^{\prime }<\theta <56^{\prime }$ for $\xi _+$ and $28^{\prime }<\theta <178^{\prime }$ for $\xi _-$. We perform the standard Bayesian likelihood analysis for cosmological inference from the measured cosmic shear TPCFs, including contributions from intrinsic alignment of galaxies as well as systematic effects from PSF model errors, shear calibration uncertainty, and source redshift distribution errors. We adopt a covariance matrix derived from realistic mock catalogs constructed from full-sky gravitational lensing simulations that fully account for survey geometry and measurement noise. For a flat $\Lambda$ cold dark matter model, we find $S\,_8 \equiv \sigma _8\sqrt{\Omega _{\rm m}/0.3}=0.804_{-0.029}^{+0.032}$, and $\Omega _{\rm m}=0.346_{-0.100}^{+0.052}$. We carefully check the robustness of the cosmological results against astrophysical modeling uncertainties and systematic uncertainties in measurements, and find that none of them has a significant impact on the cosmological constraints.

scholarly journals Mapping the Dark Matter Using Weak Lensing

2005 ◽  
Vol 216 ◽  
pp. 140-151
Author(s):  
Henk Hoekstra
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Gravitational Lensing ◽  
Cosmological Parameters ◽  
Weak Lensing ◽  
Major Step ◽  
Redshift Distribution ◽  
Panoramic Cameras ◽  
The Galaxy ◽  
Cosmic Shear

Weak gravitational lensing of distant galaxies by foreground structures has proven to be a powerful tool to study the mass distribution in the universe. The advent of panoramic cameras on 4-m class telescopes has led to a first generation of surveys that already compete with large redshift surveys in terms of the accuracy with which cosmological parameters can be determined. The next surveys, which already have started taking data, will provide another major step forward. At the current level, systematics appear under control, and it is expected that weak lensing will develop into a key tool in the era of precision cosmology, provided we improve our knowledge of the non-linear matter power spectrum and the source redshift distribution. In this review we will briefly describe the principles of weak lensing and discuss the results of recent cosmic shear surveys. We show how the combination of weak lensing and cosmic microwave background measurements can provide tight constraints on cosmological parameters. We also demonstrate the usefulness of weak lensing in studies of the relation between the galaxy distribution and the underlying dark matter distribution (“galaxy biasing”), which can provide important constraints on models of galaxy formation. Finally, we discuss new and upcoming large cosmic shear surveys.

scholarly journals What does strong gravitational lensing? The mass and redshift distribution of high-magnification lenses

2020 ◽  
Vol 495 (4) ◽  
pp. 3727-3739 ◽  
Author(s):  
Andrew Robertson ◽  
Graham P Smith ◽  
Richard Massey ◽  
Vincent Eke ◽  
Mathilde Jauzac ◽  
...  
Keyword(s):  
Gravitational Lensing ◽  
Point Sources ◽  
High Magnification ◽  
Lower Mass ◽  
Redshift Distribution ◽  
Density Profiles ◽  
Massive Galaxies ◽  
Strong Gravitational Lensing ◽  
Hydrodynamical Simulations ◽  
Halo Masses

ABSTRACT Many distant objects can only be detected, or become more scientifically valuable, if they have been highly magnified by strong gravitational lensing. We use eagle and bahamas, two recent cosmological hydrodynamical simulations, to predict the probability distribution for both the lens mass and lens redshift when point sources are highly magnified by gravitational lensing. For sources at a redshift of 2, we find the distribution of lens redshifts to be broad, peaking at z ≈ 0.6. The contribution of different lens masses is also fairly broad, with most high-magnification lensing due to lenses with halo masses between 1012 and $10^{14} \mathrm{\, M_\odot }$. Lower mass haloes are inefficient lenses, while more massive haloes are rare. We find that a simple model in which all haloes have singular isothermal sphere density profiles can approximately reproduce the simulation predictions, although such a model overpredicts the importance of haloes with mass $\lt 10^{12} \mathrm{\, M_\odot }$ for lensing. We also calculate the probability that point sources at different redshifts are strongly lensed. At low redshift, high magnifications are extremely unlikely. Each z = 0.5 source produces, on average, 5 × 10−7 images with magnification greater than 10; for z = 2, this increases to about 2 × 10−5. Our results imply that searches for strongly lensed optical transients, including the optical counterparts to strongly lensed gravitational waves, can be optimized by monitoring massive galaxies, groups, and clusters rather than concentrating on an individual population of lenses.

Nonlocal Gravity

2017 ◽  
Author(s):  
Bahram Mashhoon
Keyword(s):  
Gravitational Field ◽  
Gravitational Lensing ◽  
Past History ◽  
Lorentz Invariance ◽  
Minkowski Spacetime ◽  
Field Measurements ◽  
Local Principle ◽  
History Of ◽  
Expansion Of The Universe ◽  
Nearby Galaxies

A postulate of locality permeates through the special and general theories of relativity. First, Lorentz invariance is extended in a pointwise manner to actual, namely, accelerated observers in Minkowski spacetime. This hypothesis of locality is then employed crucially in Einstein’s local principle of equivalence to render observers pointwise inertial in a gravitational field. Field measurements are intrinsically nonlocal, however. To go beyond the locality postulate in Minkowski spacetime, the past history of the accelerated observer must be taken into account in accordance with the Bohr-Rosenfeld principle. The observer in general carries the memory of its past acceleration. The deep connection between inertia and gravitation suggests that gravity could be nonlocal as well and in nonlocal gravity the fading gravitational memory of past events must then be taken into account. Along this line of thought, a classical nonlocal generalization of Einstein’s theory of gravitation has recently been developed. In this nonlocal gravity (NLG) theory, the gravitational field is local, but satisfies a partial integro-differential field equation. A significant observational consequence of this theory is that the nonlocal aspect of gravity appears to simulate dark matter. The implications of NLG are explored in this book for gravitational lensing, gravitational radiation, the gravitational physics of the Solar System and the internal dynamics of nearby galaxies as well as clusters of galaxies. This approach is extended to nonlocal Newtonian cosmology, where the attraction of gravity fades with the expansion of the universe. Thus far only some of the consequences of NLG have been compared with observation.

Inclination Effects in Spiral Galaxy Gravitational Lensing

1997 ◽  
Vol 486 (2) ◽  
pp. 681-686 ◽  
Author(s):  
Ariyeh H. Maller ◽  
Ricardo A. Flores ◽  
Joel R. Primack
Keyword(s):  
Spiral Galaxy ◽  
Gravitational Lensing
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