Observations of Outflowing UV Absorbers in NGC 4051 with the Cosmic Origins Spectrograph

TL;DR

This study uses HST/COS, Chandra, and Suzaku observations to analyze UV and X-ray absorbers in NGC 4051, revealing multiple kinematic components with stable properties over a decade and highlighting the dominance of highly ionized gas in mass loss.

Contribution

First simultaneous UV and X-ray observations of NGC 4051 revealing stable absorption components and clarifying the ionization states responsible for mass loss.

Findings

Nine UV absorption components identified with no significant change over 10 years.

UV absorbers' velocities align with the O VII profile after correction.

High ionization gas dominates the mass loss rate, with minimal UV signature.

Abstract

We present new Hubble Space Telescope (HST)/Cosmic Origins Spectrograph observations of the Narrow-Line Seyfert 1 galaxy NGC 4051. These data were obtained as part of a coordinated observing program including X-ray observations with the Chandra/High Energy Transmission Grating (HETG) Spectrometer and Suzaku. We detected nine kinematic components of UV absorption, which were previously identified using the HST/Space Telescope Imaging Spectrograph. None of the absorption components showed evidence for changes in column density or profile within the \sim 10 yr between the STIS and COS observations, which we interpret as evidence of 1) saturation, for the stronger components, or 2) very low densities, i.e., n_H < 1 cm^-3, for the weaker components. After applying a +200 km s^-1 offset to the HETG spectrum, we found that the radial velocities of the UV absorbers lay within the O VII profile. Based on photoionization models, we suggest that, while UV components 2, 5 and 7 produce significant O VII absorption, the bulk of the X-ray absorption detected in the HETG analysis occurs in more highly ionized gas. Moreover, the mass loss rate is dominated by high ionization gas which lacks a significant UV footprint.