A new VLA/e-MERLIN limit on central images in the gravitational lens system CLASS B1030+074

We present new VLA 22-GHz and e-MERLIN 5-GHz observations of
CLASS B1030+074, a two-image strong gravitational lens system whose background source is a compact at-spectrum radio quasar. In such systems we expect a third image of the background source to form close to the centre of the lensing galaxy. The existence and brightness of such images is important for investigation of the central mass distributions of lensing galaxies, but only one secure detection has been made so far in a galaxy-scale lens system. The noise levels achieved in our new B1030+074 images reach 3 μ Jy beam^-1 and represent an improvement in central image constraints of nearly an order of magnitude over previous work, with correspondingly better resulting limits on the shape of the central mass prole of the lensing galaxy. Simple models with an isothermal outer power law slope now require either the inuence of a central supermassive black hole, or an inner power law slope very close to isothermal, in order to suppress the central image below our detection limit. Using the central mass proles inferred from light distributions in Virgo galaxies, moved to z = 0:5, and matching to the observed Einstein radius, we now nd that 45% of such mass proles should give observable central images, 10% should give central images with a flux density still below our limit, and the remaining
systems have extreme demagnication produced by the central SMBH. Further
observations of similar objects will therefore allow proper statistical constraints to be placed on the central properties of elliptical galaxies at high redshift.