Multi-epoch properties of the warm absorber in the Seyfert 1 galaxy NGC 985

TL;DR

This study analyzes multi-epoch X-ray spectra of NGC 985 to characterize its warm absorbers, revealing their properties, variability, and potential impact on galaxy feedback mechanisms.

Contribution

It provides a detailed multi-epoch analysis of warm absorber components in NGC 985, including their ionization, kinematics, and response to flux changes, which was not previously characterized.

Findings

Up to four warm absorber components identified with varying ionization and velocities.

The fastest component accounts for significant kinetic energy, potentially influencing galaxy feedback.

Absorber components are located at pc-scale distances, with some extending up to tens of parsecs.

Abstract

(Abridged) NGC 985 was observed by XMM-Newton twice in 2015, revealing that the source was coming out from a soft X-ray obscuration event that took place in 2013. These kinds of events are possibly recurrent since a previous XMM-Newton archival observation in 2003 also showed signatures of partial obscuration. We have analyzed the high-resolution X-ray spectra of NGC 985 obtained by the RGS in 2003, 2013, and 2015 in order to characterize the ionized absorbers superimposed to the continuum and to study their response as the ionizing flux varies. We found that up to four warm absorber (WA) components were present in the grating spectra of NGC 985, plus a mildy ionized (log xi ranging between 0.2 and 0.5) obscuring (log N(H) of about 22.3) wind outflowing at about 6000 km/s. The absorbers have a log N(H) ranging from 21 to about 22.5, and ionization parameters ranging from 1.6 to 2.9. The most ionized component is also the fastest, moving away at 5100 km/s, while the others outflow in two kinematic regimes, at about 600 and 350 km/s. These components showed variability at different time scales in response to changes in the ionizing continuum. Assuming that these changes are due to photoionization we have obtained upper and lower limits on the density of the gas and therefore on its distance, finding that the closest two components are at pc-scale distances, while the rest may extend up to tens of pc from the central source. The fastest, most ionized WA component accounts for the bulk of the kinetic luminosity injected back into the ISM of the host galaxy, which is on the order of 0.8% of the bolometric luminosity of NGC 985. According to the models, this amount of kinetic energy per unit time would be sufficient to account for cosmic feedback.