scholarly journals GRAVITATIONAL LENSING STATISTICS AND CONSTRAINTS ON THE COSMOLOGICAL CONSTANT REVISITED

2000 ◽  
Vol 15 (05) ◽  
pp. 697-723 ◽  
Author(s):  
YU-CHUNG N. CHENG ◽  
LAWRENCE M. KRAUSS
Keyword(s):  
Cosmological Constant ◽  
Gravitational Lensing ◽  
Velocity Dispersion ◽  
A Value ◽  
Galaxy Distribution ◽  
Systematic Uncertainties ◽  
Luminosity Functions ◽  
Likelihood Analysis ◽  
The Galaxy ◽  
Velocity Dispersions

We re-analyze constraints on the cosmological constant that can be obtained by examining the statistics of strong gravitational lensing of distant quasars by intervening galaxies, focusing on uncertainties in galaxy models (including velocity dispersion, luminosity functions, core radii and magnification bias effects) and on the parameters of the galaxy distribution and luminosity functions. In the process we derive new results on magnification biasing for galaxy lenses with nonzero core radii, and on how to infer the proper velocity dispersions appropriate for use in lensing statistics. We argue that the existing data do not disfavor a large cosmological constant. In fact, for a set of reasonable parameter choices, using the results of five optical quasar lensing surveys we find that a maximum likelihood analysis favors a value of Ω0 in the range ≈ 0.25–0.55 in a flat universe. An open cosmology is not favored by the same statistical analysis. Systematic uncertainties are likely to be dominant, however, as these results are sensitive to uncertainties in our understanding of galaxy luminosity functions, and dark matter velocity dispersions, as well as the choice of lensing survey, and to a lesser extent the existence of core radii. Further observational work will be required before it is possible to definitively distinguish between cosmological models on the basis of gravitational lensing statistics.

scholarly journals The prevalence and physical properties of extremely low-luminosity galaxies in the early universe

2019 ◽  
Vol 15 (S352) ◽  
pp. 19-19
Author(s):  
Rychard Bouwens
Keyword(s):  
Physical Properties ◽  
Galaxy Clusters ◽  
Early Universe ◽  
Gravitational Lensing ◽  
Stellar Population ◽  
Space Telescope ◽  
James Webb Space Telescope ◽  
Luminosity Functions ◽  
The Galaxy ◽  
Stellar Masses

AbstractGravitational lensing from galaxy clusters has great potential for deriving the prevalence and physical properties of ultra-faint galaxies at early times, with recent very impressive results from the Hubble Frontier Fields program. Important issues in deriving the most accurate results are accurate constraints on source sizes and a robust treatment of uncertainties in the magnification models. Using > 3300 z = 2 – 10 galaxies behind the 6 Hubble Frontier Fields clusters and a forwards modeling approach, I describe the efforts of my collaborators and me to map out the galaxy luminosity functions at ∼ − 13 mag from z ∼ 9 to z ∼ 2, i.e, a factor of 1000 below Lå and to the typical luminosity of galaxies suspected to drive cosmic reionization. Additionally, I discuss the constraints we can obtain on the properties of faint sources, in particular their stellar masses, mass-to-light ratios, colors, and stellar population ages. I conclude with a prospective on using cluster lenses to study the distant universe with the James Webb Space Telescope.

scholarly journals Characterising filaments in the SDSS volume from the galaxy distribution

2020 ◽  
Vol 642 ◽  
pp. A19 ◽  
Author(s):  
Nicola Malavasi ◽  
Nabila Aghanim ◽  
Marian Douspis ◽  
Hideki Tanimura ◽  
Victor Bonjean
Keyword(s):  
Large Scale ◽  
Sloan Digital Sky Survey ◽  
Specific Method ◽  
Redshift Surveys ◽  
Galaxy Distribution ◽  
Systematic Uncertainties ◽  
Sky Survey ◽  
The Galaxy ◽  
Free Parameters ◽  
The Universe

Detecting the large-scale structure of the Universe based on the galaxy distribution and characterising its components is of fundamental importance in astrophysics but is also a difficult task to achieve. Wide-area spectroscopic redshift surveys are required to accurately measure galaxy positions in space that also need to cover large areas of the sky. It is also difficult to create algorithms that can extract cosmic web structures (e.g. filaments). Moreover, these detections will be affected by systematic uncertainties that stem from the characteristics of the survey used (e.g. its completeness and coverage) and from the unique properties of the specific method adopted to detect the cosmic web (i.e. the assumptions it relies on and the free parameters it may employ). For these reasons, the creation of new catalogues of cosmic web features on wide sky areas is important, as this allows users to have at their disposal a well-understood sample of structures whose systematic uncertainties have been thoroughly investigated. In this paper we present the filament catalogues created using the discrete persistent structure extractor tool in the Sloan Digital Sky Survey (SDSS), and we fully characterise them in terms of their dependence on the choice of parameters pertaining to the algorithm, and with respect to several systematic issues that may arise in the skeleton as a result of the properties of the galaxy distribution (such as Finger-of-God redshift distortions and defects of the density field that are due to the boundaries of the survey).

scholarly journals Morphology, Stellar Kinematics and Dynamics of Barred Galaxies

1983 ◽  
Vol 100 ◽  
pp. 193-196
Author(s):  
John Kormendy
Keyword(s):  
Velocity Dispersion ◽  
Rotation Velocity ◽  
Stellar Kinematics ◽  
Barred Galaxies ◽  
Circular Velocity ◽  
Local Ratio ◽  
The Galaxy ◽  
Stellar Velocity ◽  
Random Motions ◽  
Velocity Dispersions

A brief review is given of the morphology of barred galaxies, following Kormendy (1981, 1982). The features illustrated include bulges, bars, disks, lenses, and inner and outer rings.Most of the paper is devoted to a detailed discussion of the absorption-line velocity field of the prototypical SBO galaxy NGC 936. The stars in the bar region show systematic non-circular streaming motions, with average orbits which are elongated parallel to the bar. Beyond the end of the bar, the data are consistent with circular orbits. The bar region also shows large random motions: the velocity dispersion at one-half of the radius of the bar is 1/2–2/3 as large as the maximum circular velocity. The observed kinematics are qualitatively and quantitatively similar to the behavior of n-body models by Miller and Smith (1979) and by Hohl and Zang (1979). The galaxy and the models show similar radial dependences of simple dimensionless parameters that characterize the dynamics. These include the local ratio of rotation velocity to velocity dispersion, which measures the relative importance of the ordered and random motions discussed above. Also similar are the residual streaming motions (relative to the circular velocity) in a frame of reference rotating with the bar. Circulation is in the same direction as rotation in all galaxies studied to date. Thus, except for the fact that NGC 936 has a slightly larger velocity dispersion, both n-body models are good first-order approximations to bars. Thus bars are different from elliptical galaxies, which in general are also triaxial, but which rotate slowly. This study of NGC 936 will be published in Kormendy (1983).A brief discussion is given of the kinematics of lens components. In both barred and unbarred galaxies, the velocity dispersions in the inner parts of lenses are large. The ratio of rotational to random kinetic energy is ∼ 1/2 at 1/3–1/2 of the radius of the lens. This ratio then decreases to small values at the rim of the lens. Thus at least some kinds of disk components have large stellar velocity dispersions, even in unbarred galaxies.

scholarly journals An adapted filter function for density split statistics in weak lensing

2020 ◽  
Vol 642 ◽  
pp. A161
Author(s):  
Pierre Burger ◽  
Peter Schneider ◽  
Vasiliy Demchenko ◽  
Joachim Harnois-Deraps ◽  
Catherine Heymans ◽  
...  
Keyword(s):  
Gravitational Lensing ◽  
Independent Set ◽  
Matched Pair ◽  
Weak Lensing ◽  
Number Density ◽  
Shape Distortion ◽  
Filter Function ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
Total Matter

Context. The density split statistics in weak gravitational lensing analyses probes the correlation between regions of different (foreground) galaxy number densities and their weak lensing signal, which is measured by the shape distortion of background galaxies. Aims. In this paper, we reconsider density split statistics, by constructing a new angular filter function that is adapted to the expected relation between the galaxy number density and shear pattern, in a way that the filter weighting the galaxy number density is matched to the filter that is used to quantify the shear signal. Methods. We used the results of numerical ray-tracing simulations, specifically through the Millennium Simulation supplemented by a galaxy distribution based on a semi-analytic model, to construct a matched pair of adapted filter functions for the galaxy density and the tangential shear signal. We compared the performance of our new filter to the previously used top-hat filter, applying both to a different and independent set of numerical simulations (SLICS, cosmo-SLICS). Results. We show that the adapted filter yields a better correlation between the total matter and the galaxy distribution. Furthermore, the adapted filter provides a larger signal-to-noise ratio to constrain the bias between the total matter and the galaxy distribution, and we show that it is, in general, a more sensitive discriminator between different cosmologies, with the exception of cosmologies with very large σ8 values. All analyses lead to the conclusion that our adapted filter should be favoured in future density split statistic works.

scholarly journals Vertical abundances variation in the galaxy: The case of PN

1997 ◽  
Vol 180 ◽  
pp. 406-406
Author(s):  
F. Cuisinier ◽  
J. Köppen
Keyword(s):  
Vertical Structure ◽  
Velocity Dispersion ◽  
Thin Disk ◽  
Scale Height ◽  
Young Stars ◽  
Low Velocity ◽  
The Galaxy ◽  
Different Populations ◽  
Velocity Dispersions

The vertical structure of the Galaxy is stratified in different populations. Gas and young stars have a low velocity dispersion (about 10 km/s) and thus are confined in a very thin disk (100 pc of scale height). Old stars have larger velocity dispersions, and are thus encountered up to a few kpc.

scholarly journals Evidence for Dark Matter in Galactic Systems

1987 ◽  
Vol 117 ◽  
pp. 97-110
Author(s):  
Marc Davis
Keyword(s):  
Dark Matter ◽  
Observational Studies ◽  
Reliable Estimate ◽  
Spherically Symmetric ◽  
Groups Of Galaxies ◽  
A Value ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
Large Clusters ◽  
Weak Trend

The evidence for dark matter in binaries and groups of galaxies is very strong, and is seen in all recent observational studies. Measurements of mass in galactic systems is possible on scales ranging from 50 kpc using virial analysis of binary galaxies to 15 Mpc using Virgocentric infall analysis. The Ω estimates derived from these studies are generally consistent with Ω < 0.2, with a fairly weak trend toward larger Ω estimates on larger scales. However, measurements of the galaxy distribution in the IRAS catalog yields a dipole anisotropy consistent in direction with the microwave dipole anisotropy, suggesting that the local galaxy distribution is responsible for the microwave velocity. This will eventually provide the most reliable estimate of Ω, and is likely to result in a value somewhat larger than previous estimates on smaller scales. Study of the velocity field around large clusters in cosmological n-body experiments provides a useful guide for understanding the limitations of the spherically symmetric models of Virgocentric infall. We point out a number of biases that could affect the existing Virgocentric flow studies.

scholarly journals Galaxies, Clusters and Fluctuations

1988 ◽  
Vol 130 ◽  
pp. 215-220
Author(s):  
Richard Schaeffer
Keyword(s):  
Luminosity Function ◽  
Two Dimensions ◽  
Many Body ◽  
Microwave Background ◽  
Scale Invariant ◽  
Galaxy Distribution ◽  
Luminosity Functions ◽  
The Galaxy ◽  
The Many ◽  
Galaxy Luminosity Function

The luminosity function of galaxies and clusters as well as their correlations can be calculated assuming the many-body correlation functions are scale invariant. The same hypothesis leads to predictions on the fractal dimension of the galaxy distribution. The latter is found to be bifractal that is characterized by two dimensions D=3−γ in the cluster region, and D = (3−γ)(2+α) in the nearly empty regions, α being the index introduced by Schechter for the galaxy luminosity function. Finally, the same models lead to predictions for the evolution of the cluster and x-ray luminosity functions, as well as for the Sunyaev-Zeldovich effect due to all virialized clusters, which is found to be large and to produce fluctuations of order 10−5 at sub-arc minute scalar in the microwave background.

scholarly journals Cosmological analysis of a Dvali-Gabadadze-Porrati stable model with H(z) observations

2018 ◽  
Vol 64 (6) ◽  
pp. 584 ◽  
Author(s):  
Gabriela Bárcenas ◽  
Celia Escamilla ◽  
Miguel Ángel García Aspeitia
Keyword(s):  
Cosmological Constant ◽  
Cosmic Acceleration ◽  
Stable Model ◽  
Galaxy Distribution ◽  
Observational Test ◽  
The Galaxy

In this paper, we will present a Dvali-Gabadadze-Porrati stable model in order to perform an observational test using $H(z)$ data and radial BAO scale in the galaxy distribution. In this vein, we study the tension between constraints on the cosmological constant $\Lambda$ and the crossover scale $r_c$, which is associated with the DGP model. Our results show that observations do not favor the DGP stable model as a possible candidate to fit to the observations of the late cosmic acceleration.

SAMPLE INCOMPLETENESS IN THE STUDY OF THE QUASAR-GALAXY ASSOCIATIONS AS A RESULT OF GRAVITATIONAL LENSING

1998 ◽  
Vol 07 (03) ◽  
pp. 463-469
Author(s):  
ZONG-HONG ZHU ◽  
XIANG-PING WU
Keyword(s):  
Gravitational Lensing ◽  
Velocity Dispersion ◽  
High Redshift ◽  
High Amplitude ◽  
Enhancement Factors ◽  
Large Velocity ◽  
The Galaxy ◽  
Number Counts

For decades, the angular associations between faint galaxies and high redshift quasars have remained to be a well-known puzzle, which is often cited as an evidence for the noncosmological origin of quasar redshifts. This happens because the attempt at interpreting the phenomenon as being due to gravitational lensing fails in producing the reported high amplitude of the quasar-galaxy associations unless some unconventional hypotheses are made such as an extremely large velocity dispersion for galaxies, a serious contamination of the overall quasar number counts or a strong matter clustering on galaxy scale. While there are good reasons to believe that the magnification bias should be a natural cause for the quasar-galaxy associations, we re-address the question by taking into account an important factor that has been overlooked in previous studies: The expected amplitude of the association in the framework of gravitational lensing depends sensitively on the quasar limiting magnitude, whereas none of the quasar samples in the measurements is actually complete. Taking this correction into account our predictions of the galaxy enhancement factors based on a simple lensing model are essentially consistent with observations, thus providing a helpful clue to eventually resolving the longstanding puzzle in astrophysics.

Sign in / Sign up

Export Citation Format

Share Document