The Double Quasar 1548+115a,b as a Gravitational Lens

Richard, Iii Gott J.; Gunn, James E.

doi:10.1086/181517

Cited by 39 publications

(20 citation statements)

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“…where is the velocity dispersion (Gott & Gunn 1974 ;p v Turner et al 1984 ;Schneider, Ehlers, & Falco 1992). This simple model can describe the Ñat rotation curves of galaxies and many basic features of gravitational lensing.…”

Section: Lensing By a Singular Isothermal Spherementioning

confidence: 99%

“…This simple model can describe the Ñat rotation curves of galaxies and many basic features of gravitational lensing. Although the gravitational lensing by an SIS has been well studied in the literature (Gott & Gunn 1974 ;Turner et al 1984 ;Narayan & White 1988 ;Kochanek 1995), we present it here since we are using an updated CDM power spectrum, and we want to compare its results with those for the NFW and the GNFW cases. We note that Narayan & White (1988) have only calculated the lensing probability for the SCDM model and normalized the CDM power spectrum by numerical simulations ; Kochanek (1995) has calculated all SCDM, OCDM, and LCDM models but normalized the power spectrum by COBE, which gives a very large value of h~1.…”

Section: Lensing By a Singular Isothermal Spherementioning

confidence: 99%

“…The most critical feature for lensing is the steepness of the central density proÐle, which may be parameterized by the central slope [a. The mass density proÐle is often taken to be the singular isothermal sphere (SIS ; a \ 2 ; Gott & Gunn 1974 ;Turner et al 1984). Although the SIS proÐle is simple, it does not Ðt the CDM simulation results.…”

Section: Introductionmentioning

confidence: 99%

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Semianalytical Models for Lensing by Dark Halos. I. Splitting Angles

Li¹,

Ostriker²

2002

ApJ

152

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We use the semianalytical approach to analyze gravitational lensing of remote quasars by foreground dark halos in various cold dark matter (CDM) cosmologies in order to determine the sensitivity of the predictions for probabilities of image separations to the input assumptions regarding the properties of halos and cosmological models. The power spectrum of primordial Ñuctuations is normalized by the cluster abundance constraints. The mass function of dark halos is assumed to be given by the PressSchechter function. The mass density proÐle of dark halos is alternatively taken to be the singular isothermal sphere (SIS), the Navarro-Frenk-White (NFW) proÐle, or the generalized NFW proÐle. The cosmologies being considered include the EinsteinÈde Sitter model (SCDM), the open model (OCDM), and the Ñat "-model (LCDM). As expected, we Ðnd that the lensing probability is extremely sensitive to the mass density proÐle of lenses (dark halos) and somewhat less so to the mean mass density in the universe and the amplitude of primordial Ñuctuations. NFW halos are very much less e †ective in producing multiple images than SIS halos. For NFW lenses, the SCDM model produces fewer lensing events than the OCDM/LCDM models by 2 orders of magnitude. For SIS lenses, the SCDM model produces more lensing events with small splitting angles and fewer lensing events with large splitting angles than the OCDM/LCDM models, which is due to the fact that for large-mass halos, the PressSchechter function is very sensitive to the amplitude of primordial Ñuctuations. In all cases the di †erence between the OCDM model and the LCDM model is not dramatic. None of these models are consistent with current observations : the SIS models predict too many large splitting lenses, while the NFW models predict too few small splitting lenses. Essentially, the observed high ratio of small splitting to large splitting lenses is not predicted correctly. This indicates that there must be at least two populations of halos in the universe : small-mass halos with a steep inner density slope and large-mass halos with a shallow inner density slope. A combination of SIS and NFW halos can reasonably reproduce the current observations if we choose the mass for the transition from SIS to NFW to be D1013 as might M _ , plausibly occur because of baryonic cooling and contraction in lower mass systems. Additionally, there is a tendency for CDM models to have too much power on small scales, i.e., too much mass concentration. From our sensitivity studies it appears that the cures proposed for other apparent difficulties of CDM would help here as well, an example being the warm dark matter variant, which is shown to produce fewer large splitting lenses than the corresponding CDM model by 1 order of magnitude.

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Section: Lensing By a Singular Isothermal Spherementioning

confidence: 99%

Section: Lensing By a Singular Isothermal Spherementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Semianalytical Models for Lensing by Dark Halos. I. Splitting Angles

Li¹,

Ostriker²

2002

ApJ

152

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“…Gravitational lensing by galaxies and clusters produces two different effects in QSO surveys. At bright magnitudes, where QSO counts are steep, a positive correlation of QSOs and foreground galaxies or clusters can be produced, as objects intrinsically fainter than the magnitude limit are amplified and hence artificially added to the sample (Gott & Gunn 1974). At fainter magnitudes, where the QSO number count slope is much flatter, it is the reduction of the observed area behind the foreground lenses which dominates, producing a deficit in the background QSO number count (Wu 1994).…”

Section: Introductionmentioning

confidence: 99%

Statistical lensing of faint QSOs by galaxy clusters

Croom

Shanks

1999

Monthly Notices of the Royal Astronomical Society

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We investigate the anti-correlation between faint high redshift QSOs and low redshift galaxy groups found by Boyle, Fong & Shanks (1988), on the assumption that it is caused by gravitational lensing of a flat QSO number count, rather than any other systematic effect (e.g dust). An isothermal sphere lens model, requires a velocity dispersion of 1286+72-91 km/s. Addition of a constant density plane reduces this to 1143+109-153 km/s, while the plane density is 0.081+-0.032h g/cm**2. Both these values are considerably larger than the 400-600km/s expected for poor clusters and groups and imply that the mass associated with such groups is ~4 times larger than inferred from virial analyses. If due to lensing, this measurement clearly tends to favour high values of Omega_0. We demonstrate how an estimate of Omega_0 may be obtained, finding Omega_0=1.3(n/3x10^-4h^3Mpc^-3)(r/1Mpc)(sigma/1286km/s)^2. Systematic uncertainties in r, the extent of the anti-correlation, and n, the group space density, currently dominate this determination, but this will be a route to estimating Omega_0 in improved galaxy-QSO datasets where systematics can be better controlled. We compared our result to that of Williams & Irwin (1998) who find a positive correlation between bright LBQS QSOs and APM galaxies. Adapting the analysis of Williams & Irwin to our use of galaxy groups, we find agreement between the amplitude of the positive cross-correlation found for bright QSOs and the negative cross-correlation found for faint QSOs. This analysis leads to a common estimate of Omega_0*sigma_8~3-4. This, however, is significantly higher than indicated from several other analyses. Further tests of the accuracy of galaxy-QSO cross-correlations and their implications for Omega_0 and sigma_8 will soon be available from the new 2dF QSO catalogue.Comment: Alteration to astro-ph abstrac

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“…Bias effects alone cannot be responsible for these correlations (Burbidge 2001;Hoyle & Burbidge 1996;Benítez et al 2001). Weak gravitational lensing by dark matter has been proposed as the cause of these correlations (Gott & Gunn 1974;Schneider 1989;Wu 1996;Burbidge et al 1997), although this seems to be insufficient to explain them (Burbidge et al 1997;Burbidge 2001;Benítez et al 2001;Gaztañaga 2003;Jain et al 2003), and cannot work at all for the correlations with the brightest and nearest galaxies. The statistical relevance of these associations is still a matter of debate (Sluse et al 2003).…”

Section: Anomalous Redshift Problemmentioning

confidence: 99%

The field surrounding NGC 7603: Cosmological or non-cosmological redshifts?

López-Corredoira

Gutiérrez

2004

A&A

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Abstract. We present new observations of the field surrounding the Seyfert galaxy NGC 7603, where four galaxies with different redshifts -NGC 7603 (z = 0.029), NGC 7603B (z = 0.057) and two fainter emission line galaxies (z = 0.245 and z = 0.394) -are apparently connected by a narrow filament, leading to a possible case of anomalous redshift. The observations comprise broad and narrow band imaging and intermediate resolution spectroscopy of some of the objects in the field. The new data confirm the redshift of the two emission-line objects found within the filament connecting NGC 7603 and NGC 7603B, and settles their type with better accuracy. Although both objects are point-like in ground based images, using HST archive images we show that the objects have structure with a FWHM = 0.3-0.4 arcsec. The photometry in the R-band obtained during three different campaigns spread over two years does not show any signs of variability in these objects above 0.3−0.4 mag. All the above information and the relative strength and width of the main spectral lines allow us to classify these as HII galaxies with very vigorous star formation, while the rest of the filament and NGC 7603B lack star formation. We delineate the halo of NGC 7603 out to 26.2 mag/arcsec 2 in the Sloan r band filter and find evidence for strong internal distortions. New narrow emission line galaxies at z = 0.246, 0.117 and 0.401 are also found at respectively 0.8, 1.5 and 1.7 arcmin to the West of the filament within the fainter contour of this halo. We have studied the spatial distribution of objects in the field within 1.5 arcmin of NGC 7603. We conclude that the density of QSOs is roughly within the expected value of the limiting magnitude of our observations. However, the configuration of the four galaxies apparently connected by the filament appears highly unusual. The probability of three background galaxies of any type with apparent B-magnitudes up to 16.6, 21.1 and 22.1 (the observed magnitudes, extinction correction included) being randomly projected on the filament of the fourth galaxy (NGC 7603) is ≈3 × 10 −9 . Furthermore, the possible detection of very vigorous star formation observed in the HII galaxies of the filament would have a low probability if they were background normal-giant galaxies; instead, the intensity of the lines is typical of dwarf HII galaxies. Hence, a set of coincidences with a very low probability would be necessary to explain this as a fortuitous projection of background sources. Several explanations in terms of cosmological or non-cosmological redshifts are discussed.

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The Double Quasar 1548+115a,b as a Gravitational Lens

Cited by 39 publications

References 0 publications

Semianalytical Models for Lensing by Dark Halos. I. Splitting Angles

Semianalytical Models for Lensing by Dark Halos. I. Splitting Angles

Statistical lensing of faint QSOs by galaxy clusters

The field surrounding NGC 7603: Cosmological or non-cosmological redshifts?

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