Microlensing of the broad-line region in the quadruply imaged quasar HE0435-1223

TL;DR

This study uses infrared spectra of the quadruply lensed quasar HE0435-1223 to detect microlensing effects on emission lines, providing insights into the geometry of the line-emitting regions, favoring a disk-like structure.

Contribution

First detection of microlensing effects on the broad-line region in HE0435-1223, constraining its geometry and supporting a flattened, disk-like emission region.

Findings

Microlensing affects Hα and MgII line profiles differently.

Constraints suggest a rotating ring or Keplerian disk origin.

Flux ratios show anomalies compared to smooth lens models.

Abstract

Using infrared spectra of the z = 1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO Very Large Telescope, we have detected a clear microlensing effect in images A and D. While microlensing affects the blue and red wings of the H{\alpha} line profile in image D very differently, it de-magnifies the line core in image A. The combination of these different effects sets constraints on the line-emitting region; these constraints suggest that a rotating ring is at the origin of the H{\alpha} line. Visible spectra obtained in 2004 and 2012 indicate that the MgII line profile is microlensed in the same way as the H{\alpha} line. Our results therefore favour flattened geometries for the low-ionization line-emitting region, for example, a Keplerian disk. Biconical models cannot be ruled out but require more fine-tuning. Flux ratios between the different images are also derived and confirm flux anomalies with respect to estimates from lens models with smooth mass distributions.