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.

scholarly journals Physics of a clumpy lensed galaxy at z = 1.6

2018 ◽  
Vol 619 ◽  
pp. A15 ◽  
Author(s):  
M. Girard ◽  
M. Dessauges-Zavadsky ◽  
D. Schaerer ◽  
J. Richard ◽  
K. Nakajima ◽  
...  
Keyword(s):  
Star Formation ◽  
Gravitational Lensing ◽  
Near Infrared ◽  
High Redshift ◽  
Formation Rate ◽  
Far Infrared ◽  
Rotating Disk ◽  
Cluster Galaxy ◽  
Star Forming ◽  
The Galaxy

Observations have shown that massive star-forming clumps are present in the internal structure of high-redshift galaxies. One way to study these clumps in detail with a higher spatial resolution is by exploiting the power of strong gravitational lensing which stretches images on the sky. In this work, we present an analysis of the clumpy galaxy A68-HLS115 at z = 1.5858, located behind the cluster Abell 68, but strongly lensed by a cluster galaxy member. Resolved observations with SINFONI/VLT in the near-infrared (NIR) show Hα, Hβ, [NII], and [OIII] emission lines. Combined with images covering the B band to the far-infrared (FIR) and CO(2–1) observations, this makes this galaxy one of the only sources for which such multi-band observations are available and for which it is possible to study the properties of resolved star-forming clumps and to perform a detailed analysis of the integrated properties, kinematics, and metallicity. We obtain a stability of υrot/σ0 = 2.73 by modeling the kinematics, which means that the galaxy is dominated by rotation, but this ratio also indicates that the disk is marginally stable. We find a high intrinsic velocity dispersion of 80 ± 10 km s−1 that could be explained by the high gas fraction of fgas = 0.75 ± 0.15 observed in this galaxy. This high fgas and the observed sSFR of 3.12 Gyr−1 suggest that the disk turbulence and instabilities are mostly regulated by incoming gas (available gas reservoir for star formation). The direct measure of the Toomre stability criterion of Qcrit = 0.70 could also indicate the presence of a quasi-stable thick disk. Finally, we identify three clumps in the Hα map which have similar velocity dispersions, metallicities, and seem to be embedded in the rotating disk. These three clumps contribute together to ∼40% on the SFRHα of the galaxy and show a star formation rate density about ∼100 times higher than HII regions in the local Universe.

scholarly journals Do Lensing Statistics Rule out a Cosmological Constant?

1999 ◽  
Vol 183 ◽  
pp. 65-65
Author(s):  
M. Chiba ◽  
Y. Yoshii
Keyword(s):  
Gravitational Lensing ◽  
Globular Clusters ◽  
Luminosity Function ◽  
Velocity Dispersion ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Hubble Constant ◽  
S0 Galaxies ◽  
Internal Velocity ◽  
Rule Out

We present new calculations of the gravitational lensing statistics following recent revised knowledge of the luminosity function and internal velocity dispersion of E/S0 galaxies which work as effective lenses for background high-redshift QSOs. We show that the theoretical prediction of the lensing statistics is much smaller than previously expected. In sharp contrast with the earlier statistics supporting an Ω0 = 1 universe, the reported small lensing probability from the Hubble Space Telescope (HST) snapshot lens survey is in best agreement with a low-density, flat universe with Ω0 ≃ 0.2 and Ω0 + λ0 = 1. The age of this universe, combined with the HST measurement of a high value of the Hubble constant H0, can be reconciled with the age of the oldest globular clusters in the Milky Way (ApJ, 1997, Vol. 489, in press).

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 A distortion of very-high-redshift galaxy number counts by gravitational lensing

Nature ◽  
2011 ◽  
Vol 469 (7329) ◽  
pp. 181-184 ◽  
Author(s):  
J. Stuart B. Wyithe ◽  
Haojing Yan ◽  
Rogier A. Windhorst ◽  
Shude Mao
Keyword(s):  
Gravitational Lensing ◽  
High Redshift ◽  
Redshift Galaxy ◽  
Number Counts ◽  
Very High

scholarly journals OH/IR Stars Near the Galactic Centre

1977 ◽  
Vol 42 ◽  
pp. 438-445
Author(s):  
B. Baud
Keyword(s):  
Radial Velocity ◽  
Velocity Dispersion ◽  
Ambient Medium ◽  
Relative Increase ◽  
Galactic Centre ◽  
Ir Stars ◽  
Large Velocity ◽  
The Galaxy ◽  
Circumstellar Shell

AbstractObservations at 1612 MHz around the Galactic Centre have revealed the existence of 43 OH/IR stars. Sources within 6° longitude from the Galactic Centre appear to be associated with the central parts of the Galaxy. They have a large velocity dispersion and a mean radial velocity of 0 km s−1, indicating that there is no net rotation around the Centre. Within 2° from the Centre there is a strong relative increase in the number of sources with a velocity separation between the two emission peaks of less than 30 km s−1. This is discussed in terms of a possible interaction between the circumstellar shell and the ambient medium.

scholarly journals Ground-Based And HST Direct Imaging Of HLQs

1996 ◽  
Vol 173 ◽  
pp. 387-392
Author(s):  
J. Surdej ◽  
A.O. Jaunsen ◽  
J.-F. Claeskens ◽  
S. Gonzaga ◽  
A. Pospieszalska-Surdej ◽  
...  
Keyword(s):  
Gravitational Lensing ◽  
Mass Range ◽  
Compact Objects ◽  
Gravitational Lens ◽  
The Internet ◽  
Direct Imaging ◽  
Large Sample ◽  
The Galaxy ◽  
Number Counts

In the context of our studies on gravitational lensing effects among Highly Luminous Quasars (HLQs), we are presently compiling at STScI an archive of direct CCD frames for more than 1000 bright quasars observed with HST and ground-based telescopes. This archive will soon become publicly accessible through the Internet. On the basis of these observations, we are pursuing in a systematic way the analysis (subtraction of numerical PSFs and/or deconvolution) of the HLQ images in order to detect multiple QSO images and/or nearby foreground galaxies at very small angular separations. Residual images corresponding to several new possible multiply imaged HLQs are presented here. From the observed number and image configuration of gravitational lens candidates identified in this large sample of HLQs, it is possible to infer realistic values for parameters characterizing the galaxy deflectors, the number counts of quasars, etc. (cf. Claeskens et al. 1995ab), and also to set interesting constraints on the cosmological density of compact objects in the mass range 1010 ‒ 1012M⊙.

scholarly journals Gravitational Lensing by Elliptical Galaxies

2005 ◽  
Vol 201 ◽  
pp. 490-491
Author(s):  
Daniel J. Mortlock ◽  
Rachel L. Webster
Keyword(s):  
Cross Section ◽  
Gravitational Lensing ◽  
Velocity Dispersion ◽  
High Redshift ◽  
Elliptical Galaxies ◽  
Line Of Sight ◽  
Density Parameter ◽  
Core Radius ◽  
The Core ◽  
Weakly Dependent

The probability that high-redshift quasars are gravitationally-lensed by intervening galaxies increases rapidly with the cosmological constant, ΩΛ0 (whilst being only weakly dependent on the density parameter, Ωm0), and the low number of lenses observed implies that ΩΛ0 ≲ 0.7 (e.g. Kochanek 1996). One of many uncertainties has been the (small) core radii of elliptical galaxies, which, at least naively, reduce their lensing cross-section. However, if ellipticals are normalised relative to their observed line-of-sight velocity dispersion, σ||, then increasing the core radius must result in an increased mass normalisation (specified by the assymptotic velocity dispersion, σ∞).

scholarly journals A new model for the infrared emission of IRAS F10214+4724

2011 ◽  
Vol 7 (S284) ◽  
pp. 205-209
Author(s):  
Andreas Efstathiou ◽  
Natalie Christopher ◽  
Aprajita Verma ◽  
Ralf Siebenmorgen
Keyword(s):  
Energy Distribution ◽  
Gravitational Lensing ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Infrared Emission ◽  
Spectral Energy ◽  
New Model ◽  
Average Spectrum ◽  
Line Region ◽  
The Galaxy

AbstractWe present a new model for the infrared emission of the high redshift hyperluminous infrared galaxy IRAS F10214+4724 which takes into account recent photometric data from Spitzer and Herschel that sample the peak of its spectral energy distribution. We first demonstrate that the combination of the AGN tapered disc and starburst models of Efstathiou and coworkers, while able to give an excellent fit to the average spectrum of type 2 AGN measured by Spitzer, fails to match the spectral energy distribution of IRAS F10214+4724. This is mainly due to the fact that the ν Sν distribution of the galaxy falls very steeply with increasing frequency (a characteristic of heavy absorption by dust) but shows a silicate feature in emission. We propose a model that assumes two components of emission: clouds that are associated with the narrow-line region and a highly obscured starburst. The emission from the clouds must suffer significantly stronger gravitational lensing compared to the emission from the torus to explain the observed spectral energy distribution.

scholarly journals Scale dependence of galaxy biasing investigated by weak gravitational lensing: An assessment using semi-analytic galaxies and simulated lensing data

2018 ◽  
Vol 613 ◽  
pp. A15 ◽  
Author(s):  
Patrick Simon ◽  
Stefan Hilbert
Keyword(s):  
Gravitational Lensing ◽  
Spatial Scales ◽  
Scale Dependence ◽  
Reconstruction Technique ◽  
Weak Gravitational Lensing ◽  
Physical Scale ◽  
The Galaxy ◽  
Galaxy Bias ◽  
The Impact ◽  
Lens Galaxies

Galaxies are biased tracers of the matter density on cosmological scales. For future tests of galaxy models, we refine and assess a method to measure galaxy biasing as a function of physical scalekwith weak gravitational lensing. This method enables us to reconstruct the galaxy bias factorb(k) as well as the galaxy-matter correlationr(k) on spatial scales between 0.01hMpc−1≲k≲ 10hMpc−1for redshift-binned lens galaxies below redshiftz≲ 0.6. In the refinement, we account for an intrinsic alignment of source ellipticities, and we correct for the magnification bias of the lens galaxies, relevant for the galaxy-galaxy lensing signal, to improve the accuracy of the reconstructedr(k). For simulated data, the reconstructions achieve an accuracy of 3–7% (68% confidence level) over the abovek-range for a survey area and a typical depth of contemporary ground-based surveys. Realistically the accuracy is, however, probably reduced to about 10–15%, mainly by systematic uncertainties in the assumed intrinsic source alignment, the fiducial cosmology, and the redshift distributions of lens and source galaxies (in that order). Furthermore, our reconstruction technique employs physical templates forb(k) andr(k) that elucidate the impact of central galaxies and the halo-occupation statistics of satellite galaxies on the scale-dependence of galaxy bias, which we discuss in the paper. In a first demonstration, we apply this method to previous measurements in the Garching-Bonn Deep Survey and give a physical interpretation of the lens population.

scholarly journals Anisotropy in ω Centauri and 47 Tucanae

1988 ◽  
Vol 126 ◽  
pp. 663-664
Author(s):  
G. Meylan
Keyword(s):  
Globular Clusters ◽  
Velocity Dispersion ◽  
Dynamical Models ◽  
Comprehensive Description ◽  
Great Opportunity ◽  
The Galaxy

The southern sky gives us the great opportunity to observe two among the brightest and nearest globular clusters of the Galaxy: ω Cen and 47 Tuc. For these giant clusters, we present the comparison between observations and King-Michie multi-mass dynamical models with anisotropy in the velocity dispersion. A more comprehensive description of this work is to be published (Meylan 1986a,b).

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