A doubled double hotspot in J0816+5003 and the logarithmic slope of the lensing potential

TL;DR

This paper analyzes high-resolution observations of a doubly-lensed radio hotspot in galaxy J0816+5003 to measure the lensing potential's slope over a large radius range, finding it close to isothermal.

Contribution

It provides the first detailed measurement of the lensing potential slope over a large radius range using improved imaging and registration techniques.

Findings

Lensing potential slope is close to isothermal.

Measured impact parameters are less than 500 pc.

Lens and source redshifts are 0.332 and >1.

Abstract

We present an analysis of observations of the doubly-lensed double hotspot in the giant radio galaxy J0816+5003 from MERLIN, MDM, WIYN, WHT, UKIRT and the VLA. The images of the two hotspot components span a factor of two in radius on one side of the lensing galaxy at impact parameters of less than 500pc. Hence we measure the slope of the lensing potential over a large range in radius, made possible by significant improvement in the accuracy of registration of the radio and optical frame and higher resolution imaging data than previously available. We also infer the lens and source redshifts to be 0.332 and > 1 respectively. Purely on the basis of lens modelling, and independently of stellar velocity dispersion measurements, we find the potential to be very close to isothermal.