The X-ray warm absorber and nuclear obscuration in the Seyfert 1.8 galaxy ESO 113-G010

Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey n RH5 6NT, UK
e-mail: missagh.mehdipour@ucl.ac.uk

Received: 27 January 2012
Accepted: 12 April 2012

Abstract

We present the first analysis of the X-ray warm absorber and nuclear obscuration in the Seyfert 1.8 galaxy ESO 113-G010. We used archival data from a 100 ks XMM-Newtonobservation made in 2005. From high resolution spectroscopy analysis of the RGS data, we detect absorption lines originating from a warm absorber consisting of two distinct phases of ionisation, with log ξ ≈ 3.2 and 2.3 respectively. The higher-ionised component has a larger column density and outflow velocity (N_H ≈ 1.6 × 10²² cm^-2, v ≈  − 1100  km  s^-1) than the lower-ionised component (N_H ≈ 0.5 × 10²² cm^-2, v ≈  −700  km  s^-1). The shape of the optical-UV continuum and the large Balmer decrement (Hα/Hβ ~ 8) indicate significant amount of reddening is taking place in our line of sight in the host galaxy of the AGN; however, the X-ray spectrum is not absorbed by cold neutral gas intrinsic to the source. We discuss different explanations for this discrepancy between the reddening and the X-ray absorption, and suggest that the most likely solution is a dusty warm absorber. We show that dust can exist in the lower-ionised phase of the warm absorber, which causes the observed reddening of the optical-UV emission, whereas the X-rays remain unabsorbed due to lack of cold neutral gas in the ionised warm absorber. Furthermore, we have investigated the uncertainties in the construction of the spectral energy distribution (SED) of this object due to obscuration of the nuclear source and the effects this has on the photoionisation modelling of the warm absorber. We show how the assumed SEDs influence the thermal stability of each phase and whether or not the two absorber phases in ESO 113-G010can co-exist in pressure equilibrium.