On the origin of X-ray oxygen emission lines in obscured AGN

Abstract

We present the Catalog of High REsolution Spectra of Obscured Sources (CHRESOS) from the XMM-Newton Science Archive. It comprises the emission-line luminosities of H- and He-like transitions from C to Si, and the Fe 3C and Fe 3G L-shell ones. Here, we concentrate on the soft X-ray OVII(f) and OVIII Ly_alpha emission lines to shed light onto the physical processes with which their formation can be related to: active galactic nucleus vs. star forming regions. We compare their luminosity with that of two other important oxygen key lines [OIII]5007A, in the optical, and [OIV]25.89mic, in the IR. We also test OVII(f) and OVIIILy_alpha luminosities against that of continuum bands in the IR and hard X-rays, which point to different ionization processes. We probe into those processes by analyzing photoionization and colisional ionization model predictions upon our lines. We show that both scenarios can explain the formation and observed intensities of OVII(f) and OVIII Ly_alpha. By analyzing the relationships between OVII(f) and OVIII Ly_alpha, and all other observables: [OIII]5007A, [OIV]25.89mic emission lines, and MIR-12mic, FIR-60mic, FIR-100mic, 2-10 keV and 14-195 keV continuum bands, we conclude that the AGN radiation field is mainly responsible of the soft X-ray oxygen excitation.