Integral Field Spectroscopy of the Quadruply Lensed Quasar 1RXS J1131−1231: New Light on Lens Substructures

We have observed the quadruply lensed quasar 1RXS J1131-1231 with theintegral field spectrograph mode of the Kyoto Tridimensional Spectrograph IImounted on the Subaru telescope. Its field of view has covered simultaneouslythe three brighter lensed images A, B, and C, which are known to exhibitanomalous flux ratios in their continuum emission. We have found that the[OIII] line flux ratios among these lensed images are consistent with thosepredicted by smooth-lens models. The absence of both microlensing andmillilensing effects on this [OIII] narrow line region sets important limits onthe mass of any substructures along the line of sight, which is expressed asM_E < 10^5 M_solar for the mass inside an Einstein radius. In contrast, theH_beta line emission, which originates from the broad line region, shows ananomaly in the flux ratio between images B and C, i.e., a factor two smallerC/B ratio than predicted by smooth-lens models. The ratio of A/B in the H_betaline is well reproduced. We show that the anomalous C/B ratio for the H_betaline is caused most likely by micro/milli-lensing of image C. This is becauseother effects, such as the differential dust extinction and/or arrival timedifference between images B and C, or the simultaneous lensing of another pairof images A and B, are all unlikely. In addition, we have found that the broadH_beta line of image A shows a slight asymmetry in its profile compared withthose in the other images, which suggests the presence of a small microlensingeffect on this line emitting region of image A.Comment: 21 pages, 7 figures, 1 table, ApJ accepte