Modeling the [Fe II]{\lambda}1.644{\mu}m outflow and comparison with H$_2$ and H$^+$ kinematics in the inner 200 pc of NGC 1068

TL;DR

This study maps and models the inner 200 pc of NGC 1068, revealing detailed kinematics of ionized and molecular gas, and providing insights into outflow structures and their impact on the galaxy's nucleus.

Contribution

It offers high-resolution kinematic maps of [Fe II], H$_2$, and Br{ }gamma lines, modeling the outflow geometry and quantifying the mass outflow rate in NGC 1068.

Findings

[Fe II] traces a more extended outflow than [O III], indicating partial ionization and shock contributions.

The outflow has a conical or hourglass geometry with a mass outflow rate of about 1.9 M$_{}$ yr$^{-1}$.

H$_2$ gas shows radial expansion in a ring, decelerating at larger radii.

Abstract

We map the kinematics of the inner (200 pc) narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 using the instrument NIFS and adaptative optics at the Gemini North Telescope. Channel maps and position-velocity diagrams are presented at a spatial resolution of $\sim$ 10 pc and spectral resolution $\sim$ 5300 in the emission lines [Fe II] {\lambda} 1.644 {\mu}m, H$_2$ {\lambda} 2.122 {\mu}m and Br{\gamma}. The [Fe II] emission line provides a better coverage of the NLR outflow than the previously used [O III] {\lambda} 5007 emission line, extending beyond the area of the bi-polar cone observed in Br{\gamma} and [O III]. This is mainly due to the contribution of the redshifted channels to the NE of the nucleus, supporting its origin in a partial ionized zone with additional contribution from shocks of the outflowing gas with the galactic disc. We modeled the kinematics and geometry of the [Fe II] emitting gas finding good agreement with the data for outflow models with conical and lemniscate (or hourglass) geometry. We calculate a mass outflow rate $1.9^{+1.9}_{-0.7}$ M$_{\odot}~$yr$^{-1}$ but a power for the outflow of only 0.08% L$_{Bol}$. The molecular (H$_2$) gas kinematics is completely distinct from that of [Fe II] and Br{\gamma}, showing radial expansion in an off-centered $\sim$ 100 pc radius ring in the galaxy plane. The expansion velocity decelerates from $\sim$ 200 km/s in the inner border of the ring to approximately zero at the outer border where our previous studies found a 10 Myr stellar population.