Radiative Driving of the AGN Outflows in the Narrow-Line Seyfert 1 Galaxy NGC 4051

TL;DR

This study investigates ionized gas outflows in NGC 4051, revealing that radiation pressure drives the outflows originating close to the nucleus, with velocities up to 680 km/s, extending over kiloparsec scales.

Contribution

The paper introduces an improved biconical outflow model and links UV absorbers to NLR clouds, providing new insights into AGN outflow mechanisms in NGC 4051.

Findings

Outflows are launched within 0.5 pc of the nucleus.

Outflows reach up to 680 km/s at 350 pc distance.

Most outflows originate close to the nucleus and extend up to 1 kpc.

Abstract

We explore the properties of ionized gas in the nuclear and circumnuclear environment of the narrow-line Seyfert 1 galaxy NGC 4051 using spectroscopic and imaging observations from the Hubble Space Telescope (HST) and Apache Point Observatory (APO)'s ARC 3.5m Telescope. We identify an unresolved moderate-density intermediate width component and a high-density broad component in the optical emission lines from the active nucleus, as well as spatially-resolved emission extending up to $\sim$1 kpc in the AGN ionized narrow-line region (NLR) and $\sim$8 kpc in the stellar ionized host galaxy. The HST narrow-band image reveals a distinct conical structure in [O III] emission towards the NE, and the ionized gas kinematics shows up to two blueshifted velocity components, indicating outflows along the edges of a cone. We introduce an improved model of biconical outflow, with our line of sight passing through the wall of the cone, which suggests that the large number of outflowing UV absorbers seen in NGC 4051 are NLR clouds in absorption. Using the de-projection factors from the biconical geometry, we measure true outflow velocities up to 680 km s$^{-1}$ at a distance of $\sim$350 pc, however, we do not find any rotational signature inside a projected distance $\leq$ 10'' ($\sim$800 pc) from the nucleus. We compare the gas kinematics with analytical models based on a radiation-gravity formalism, which show that most of the observed NLR outflows are launched within $\sim$0.5 pc of the nucleus and can travel up to $\sim$1 kpc from this low-luminosity AGN.