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 Which Galaxy Property Best Predicts Quiescence?

2012 ◽  
Vol 8 (S295) ◽  
pp. 177-177
Author(s):  
Joel Leja ◽  
Pieter van Dokkum ◽  
Keyword(s):  
Spatial Distribution ◽  
Star Formation ◽  
Velocity Dispersion ◽  
High Redshift ◽  
Line Emission ◽  
Elliptical Galaxies ◽  
High Dispersion ◽  
Quenching Mechanism ◽  
Line Flux ◽  
Line Equivalent Width

AbstractIt is generally accepted that local elliptical galaxies assembled most of their mass in a burst of star formation between 1 < z < 3, yet today, their star formation has been almost entirely quenched. In order to constrain this quenching mechanism, we measure Hα line emission in galaxies sorted by multiple galaxy properties as a function of redshift to what galaxy parameter best predicts quiescence. This is done for samples of the most massive, most luminous, and galaxies with the highest velocity dispersion both locally (0.05 < z < 0.07 in the SDSS) and at high redshift (0.7 < z < 1.5 in 3D-HST). It is demonstrated through spectral stacking that velocity dispersion results in the lowest Hα line equivalent width both locally and at high redshift. The spatial distribution of the emission line flux is available from grism spectroscopy: the line flux from the high dispersion stack is centrally peaked and thus likely associated with AGN activity rather than star formation, strengthening this conclusion. Since velocity dispersion may also be the best predictor of halo mass (Wake et al. 2012), this may imply that the quenching mechanism is directly related to halo mass.

scholarly journals CONSTRAINING TEVES GRAVITY AS EFFECTIVE DARK MATTER AND DARK ENERGY

2007 ◽  
Vol 16 (12a) ◽  
pp. 2055-2063 ◽  
Author(s):  
HONGSHENG ZHAO
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Elliptical Galaxies ◽  
Dual Roles ◽  
Acceleration Of The Universe ◽  
The Universe

The phenomena customarily described with the standard ΛCDM model are broadly reproduced by an extremely simple model in TeVeS, Bekenstein's1 modification of general relativity motivated by galaxy phenomenology. Our model can account for the acceleration of the Universe seen at SNeIa distances without a cosmological constant, and the accelerations seen in rotation curves of nearby spiral galaxies and gravitational lensing of high-redshift elliptical galaxies without cold dark matter. The model is consistent with BBN and the neutrino mass between 0.05 eV to 2 eV. The TeVeS scalar field is shown to play the effective dual roles of dark matter and dark energy, with the amplitudes of the effects controlled by a μ function of the scalar field, called the μ essence here. We also discuss outliers to the theory's predictions on multiimaged galaxy lenses and outliers on the subgalaxy scale.

scholarly journals Modeling mass independent of anisotropy

2010 ◽  
Vol 6 (S271) ◽  
pp. 110-118
Author(s):  
Joe Wolf
Keyword(s):  
Spatial Variation ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Galaxy Cluster ◽  
Elliptical Galaxies ◽  
Line Of Sight ◽  
Dwarf Spheroidal Galaxies ◽  
Dispersion Profile ◽  
Stellar Velocity ◽  
Dwarf Elliptical Galaxies

AbstractBy manipulating the spherical Jeans equation, Wolf et al. (2010) show that the mass enclosed within the 3D deprojected half-light radius r1/2 can be determined with only mild assumptions about the spatial variation of the stellar velocity dispersion anisotropy as long as the projected velocity dispersion profile is fairly flat near the half-light radius, as is typically observed. They find M1/2 = 3 G−1 〈σ2los〉 r1/2 ≃ 4 G−1 〈σ2los〉 Re, where 〈σ2los〉 is the luminosity-weighted square of the line-of-sight velocity dispersion and Re is the 2D projected half-light radius. This finding can be used to show that all of the Milky Way dwarf spheroidal galaxies (MW dSphs) are consistent with having formed within a halo of mass approximately 3 × 109 M⊙, assuming a ΛCDM cosmology. In addition, the dynamical I-band mass-to-light ratio ϒI1/2 vs. M1/2 relation for dispersion-supported galaxies follows a U-shape, with a broad minimum near ϒI1/2 ≃ 3 that spans dwarf elliptical galaxies to normal ellipticals, a steep rise to ϒI1/2 ≃ 3,200 for ultra-faint dSphs, and a more shallow rise to ϒI1/2 ≃ 800 for galaxy cluster spheroids.

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 Shape, Color, and Distance in Weak Gravitational Flexion

2020 ◽  
Author(s):  
Joseph M Fabritius ◽  
Evan J Arena ◽  
David M Goldberg
Keyword(s):  
Gravitational Lensing ◽  
Rotational Symmetry ◽  
High Redshift ◽  
Morphological Type ◽  
Elliptical Galaxies ◽  
Early Type ◽  
Late Type ◽  
Color Measurements ◽  
Redshift Galaxy ◽  
Intrinsic Scatter

Abstract Canonically, elliptical galaxies might be expected to have a perfect rotational symmetry, making them ideal targets for flexion studies - however, this assumption hasn’t been tested. We have undertaken an analysis of low and high redshift galaxy catalogs of known morphological type with a new gravitational lensing code, Lenser. Using color measurements in the u − r bands and fit Sérsic index values, objects with characteristics consistent with early-type galaxies are found to have a lower intrinsic scatter in flexion signal than late-type galaxies. We find this measured flexion noise can be reduced by more than a factor of two at both low and high redshift.

scholarly journals A Technical Memorandum On Core Radii In Lens Statistics

1996 ◽  
Vol 173 ◽  
pp. 7-12
Author(s):  
Christopher S. Kochanek
Keyword(s):  
Cross Sections ◽  
Velocity Dispersion ◽  
Cosmological Models ◽  
Core Radius ◽  
Expected Number ◽  
Sis Model ◽  
The Core ◽  
Quantitative Estimates ◽  
Self Consistent

Quantitative estimates of lensing probabilities must be self-consistent. In particular, for asymptotically isothermal models: (1) using the (3/2)1/2 correction for the velocity dispersion overestimates the expected number of lenses by 150% and their average separations by 50%, thereby introducing large cosmological errors; (2) when a core radius is added to the SIS model, the velocity dispersion must be increased; and (3) cross sections and magnification bias cannot be separated when computing the lensing probability. When we self-consistently calculate the effects of finite core radii in flat cosmological models, we find that the cosmological limits are independent of the core radius.

Limits On The Core Radii Of JVAS/CLASS Gravitational Lenses

2005 ◽  
Vol 201 ◽  
pp. 492-493
Author(s):  
M. Norbury ◽  
N. J. Jackson ◽  
I. W. A. Browne ◽  
P. N. Wilkinson ◽  
D. Rusin
Keyword(s):  
Gravitational Lensing ◽  
High Sensitivity ◽  
Network Data ◽  
Gravitational Lenses ◽  
Core Radius ◽  
Radio Observations ◽  
The Core ◽  
Upper Limit

Gravitational lenses typically consist of either two or four images (doubles and quads) of the background source. However, it has been shown that gravitational lensing by transparent extended matter distributions should produce an odd number of images. An upper limit for the flux of the missing ‘odd image’ can be obtained using high sensitivity radio observations, such as 5GHz MERLIN (Multi-Element Radio Linked Interferometer Network) data. Limits on the ‘odd image’ flux can then be converted into an upper limit on the core radius of the lensing galaxy.

scholarly journals An HST Survey of Cores of Early-Type Galaxies

1996 ◽  
Vol 171 ◽  
pp. 105-116 ◽  
Author(s):  
John Kormendy ◽  
Yong-Ik Byun ◽  
E. A. Ajhar ◽  
Tod R. Lauer ◽  
Alan Dressler ◽  
...  
Keyword(s):  
Outer Surface ◽  
Surface Brightness ◽  
Hubble Space Telescope ◽  
Elliptical Galaxies ◽  
Core Radius ◽  
Early Type ◽  
Late Type ◽  
Fundamental Plane ◽  
The Core ◽  
Oblate Spheroidal

Photometry of the central parts of bulges and elliptical galaxies with the Hubble Space Telescope (HST) confirms and extends ground-based results. Most giant ellipticals have cuspy cores: at the “break radius” rb (formerly the core radius rc), the steep outer surface brightness profile turns down to a shallow inner power law I(r) ∝ r–γ, 0 ≤ γ ≲ 0.25. The corresponding slope of the deprojected profile is derived; the flattest cores allow box orbits to survive. Cores continue to satisfy fundamental plane parameter correlations like those found from the ground. In particular, HST confirms that the luminosity sequence of elliptical galaxies (from cDs to M 32) is physically unrelated to spheroidal galaxies like Fornax. The latter are closely related to late-type dwarfs. Low-luminosity ellipticals do not show cores: 0.5 ≲ γ ≲ 1.3. The most important new result is that global and core properties both show signs of a dichotomy between (i) low-luminosity ellipticals that rotate rapidly, that are nearly isotropic and oblate-spheroidal, that have disky-distorted isophotes, and that are coreless and (ii) giant ellipticals that are essentially nonrotating, anisotropic, and moderately triaxial, that are boxy-distorted, and that have cuspy cores.

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.

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