Multi-wavelength study of the gravitational lens system RXS J1131-1231: III. Long slit spectroscopy: micro-lensing probes the QSO structure

TL;DR

This study uses long slit spectroscopy to analyze micro-lensing effects in the gravitational lens system RXS J1131-1231, revealing detailed information about the structure and size of the quasar's emission regions and the lensing medium.

Contribution

It provides new insights into the size and structure of quasar emission regions through micro-lensing analysis using spectral decomposition techniques.

Findings

Micro-lensing de-amplifies images A and C, affecting continuum and some BLR emission.

A very broad MgII emission component originates from a more compact region.

A significant fraction of FeII emission arises from outer BLR regions and compact zones.

Abstract

(ABRIDGED) Aims: We discuss and characterize micro-lensing among the 3 brightest lensed images (A-B-C) of the gravitational lens system RXS J1131-1231 (a quadruply imaged AGN) by means of long slit optical and NIR spectroscopy. Qualitative constraints on the size of different emission regions are derived. Methods: We decompose the spectra into their individual emission components using a multi-component fitting approach. A complementary decomposition of the spectra enables us to isolate the macro-lensed fraction of the spectra independently of any spectral modelling. Results: -1. The data support micro-lensing de-amplification of images A and C. Not only is the continuum emission microlensed in those images but also a fraction of the Broad Line emitting Region (BLR).-2. Micro-lensing of a very broad component of MgII emission line suggests that the corresponding emission occurs in a region more compact than the other components of the emission line. -3. We find evidence that a large fraction of the FeII emission arises in the outer parts of the BLR. We also find very compact emitting region in the ranges 3080-3540 A and 4630-4800 A that is likely associated with FeII. -4. The OIII narrow emission line regions are partly spatially resolved. This enables us to put a lower limit of 110h^{-1} pc on their intrinsic size. -5. Analysis of MgII absorption found in the spectra indicates that the absorbing medium is intrinsic to the quasar, has a covering factor of 20%, and is constituted of small clouds homogeneously distributed in front of the continuum and BLRs. -6. Two neighbour galaxies are detected at redshifts z=0.10 and z=0.289. These galaxies are possible members of galaxy groups reported at those redshifts.