arXiv subjects

Randall B. Wayth

Publications and source records attributed to Randall B. Wayth.

59 records · Page 4Linked to original sources

arXiv2006

Lensview: Software for modelling resolved gravitational lens images

We have developed a new software tool, Lensview, for modelling resolved gravitational lens images. Based on the LensMEM algorithm, the software finds the best fitting lens mass model and source brightness distribution using a maximum entropy constraint. The method can be used with any point spread function or lens model. We review the algorithm and introduce some significant improvements. We also investigate and discuss issues associated with the statistical uncertainties of models and model parameters and the issues of source plane size and source pixel size. We test the software on simulated optical and radio data to evaluate how well lens models can be recovered and with what accuracy. For optical data, lens model parameters can typically be recovered with better than 1% accuracy and the degeneracy between mass ellipticity and power law is reduced. For radio data, we find that systematic errors associated with using processed radio maps, rather than the visibilities, are of similar magnitude to the random errors. Hence analysing radio data in image space is still useful and meaningful. The software is applied to the optical arc HST J15433+5352 and the radio ring MG1549+3047 using a simple elliptical isothermal lens model. For HST J15433+5352, the Einstein radius is 0.525" +/- 0.015 which probably includes a substantial convergence contribution from a neighbouring galaxy. For MG1549+3047, the model has Einstein radius 1.105" +/- 0.005 and core radius 0.16" 0.03. The total mass enclosed in the critical radius is 7.06 x 10^{10} Solar masses for our best model.

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arXiv2005

The lens and source of the optical Einstein ring gravitational lens ER 0047-2808

(Abridged) We perform a detailed analysis of the optical gravitational lens ER 0047-2808 imaged with WFPC2 on the Hubble Space Telescope. Using software specifically designed for the analysis of resolved gravitational lens systems, we focus on how the image alone can constrain the mass distribution in the lens galaxy. We find the data are of sufficient quality to strongly constrain the lens model with no a priori assumptions about the source. Using a variety of mass models, we find statistically acceptable results for elliptical isothermal-like models with an Einstein radius of 1.17''. An elliptical power-law model (Sigma \propto R^-beta) for the surface mass density favours a slope slightly steeper than isothermal with beta = 1.08 +/- 0.03. Other models including a constant M/L, pure NFW halo and (surprisingly) an isothermal sphere with external shear are ruled out by the data. We find the galaxy light profile can only be fit with a Sersic plus point source model. The resulting total M/L_B contained within the images is 4.7 h_65 +/-0.3. In addition, we find the luminous matter is aligned with the total mass distribution within a few degrees. The source, reconstructed by the software, is revealed to have two bright regions, with an unresolved component inside the caustic and a resolved component straddling a fold caustic. The angular size of the entire source is approx. 0.1'' and its (unlensed) Lyman-alpha flux is 3 x 10^-17 erg/s/cm^2.

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arXiv2005

A microlensing measurement of the size of the broad emission line region in the lensed QSO 2237+0305

We present spatially resolved spectroscopic images of the gravitationally lensed QSO 2237+0305 taken with the GMOS Integral Field Unit (IFU) on the Gemini North telescope. These observations have the best spatial resolution of any IFU observations of this object to date and include the redshifted CIII] and MgII QSO broad lines. Unlike Mediavilla et al. 1998, we find no evidence for an arc of resolved broad line emission in either the CIII] or MgII lines. We calculate the image flux ratios of both the integrated emission lines and the surrounding continua. The flux ratios of the CIII] and MgII emission lines are consistent with each other but differ substantially from their corresponding continuum flux ratios and the radio/mid-IR flux ratios previously published. We argue that the broad emission line region must be microlensed and the CIII] and MgII emission regions must be approximately the same size and co-located along the line-of-sight. Assuming a simple model for the broad emission line region and the continuum region, we show the size of the CIII] / MgII broad line region is ~0.06 h_{70}^{1/2} pc and the continuum region is <= 0.02 h_{70}^{1/2} pc.

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arXiv2004

H1517+656: the Birth of a BL Lac Object?

H1517+656 is an unusual source, even for a BL Lac object. It is one of the most luminous BL Lacs known, with extreme emission properties at radio, optical, and X-ray frequencies. Furthermore, in our WFPC2 snapshot survey we discovered a series of peculiar arcs describing a 2.4 arcsec radius ring surrounding the source. This paper describes follow-up observations with additional WFPC2 bands and the STIS longpass filter, which have revealed this structure to be the remnants of a very recent galaxy merger. Population synthesis modelling has shown that regions of the arcs have stellar populations with age < 20 Myrs. Additionally, the circularity of the arcs indicates that the plane of the collision and hence accretion is very close to the plane of the sky. Given that BL Lac jets are thought to be aligned with the line of sight, this observation may provide a direct link between the transfer of angular momentum in an interaction and the generation of a radio source.

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arXiv2002

The dark matter halo of the gravitational lens galaxy 0047-2808

The location of the images in a multiple-image gravitational lens system are strongly dependent on the orientation angle of the mass distribution. As such, we can use the location of the images and the photometric properties of the visible matter to constrain the properties of the dark halo. We apply this to the optical Einstein Ring system 0047-2808 and find that the dark halo is almost spherical and is aligned in the same direction as the stars to within a few degrees.

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