Evolution of the Outflows in NGC 3516

TL;DR

This study examines the evolution of outflow components in NGC 3516 using HST/COS spectra, revealing bulk motion, velocity shifts, and new absorption features, and determines the outflow's distance from the galaxy nucleus.

Contribution

It provides the first detailed analysis of outflow component evolution in NGC 3516, including velocity changes and the detection of a new absorption trough, with direct distance measurement.

Findings

Bulk motion observed in absorption components.

Detection of a new absorption trough due to Si II.

Outflow component 1 located at 67.2 parsecs from nucleus.

Abstract

We analyze the 2011 HST/COS spectrum of the Seyfert 1 galaxy NGC 3516, which demonstrates clear changes in one of the intrinsic absorption troughs (component 5), slight evidence of change in a second trough (component 6), and the appearance of a new absorption trough (component 9). We interpret both the changes and the appearance of the new trough as bulk motion across the line of sight. The implied lower limit on the transverse velocity of component 5 is 360 km/s, compared to the earlier 2001 HST/STIS spectrum, while the lower limits for components 6 and 9 are 920 km/s, based on 2009 FUSE data. Component 5 also exhibits a shift in velocity centroid. This is only the second known case of this behavior in a Seyfert galaxy. Due to the high quality of the HST/COS spectrum, we identify a previously undetected trough due to an excited state of Si II for component 1. In combination with the resonance trough of Si II and photoionization modeling, we directly determine the distance of the component 1 outflow to be 67.2 pc.