The Kiloparsec-scale Neutral Atomic Carbon Outflow in the Nearby Type-2 Seyfert Galaxy NGC 1068: Evidence for Negative AGN Feedback

TL;DR

This study uses high-resolution ALMA observations to reveal that AGN-driven outflows in NGC 1068 dissociate molecular gas, providing direct evidence of negative feedback that impacts the galaxy's interstellar medium and star formation.

Contribution

First detailed high-resolution ALMA observations of [CI] and CO emissions in NGC 1068 showing AGN outflows dissociate molecular gas, supporting the CO dissociation feedback scenario.

Findings

[CI] emission is enhanced by over 5 times in the central kpc.

The [CI]/CO ratio exceeds 1 in the outflow region.

A decelerating bicone model explains the outflow kinematics.

Abstract

Active galactic nucleus (AGN) feedback is postulated as a key mechanism for regulating star formation within galaxies. Studying the physical properties of the outflowing gas from AGN is thus crucial for understanding the co-evolution of galaxies and supermassive black holes. Here we report 55 pc resolution ALMA neutral atomic carbon [CI] $^3P_1\text{-}^3P_0$ observations toward the central 1 kpc of the nearby type-2 Seyfert galaxy NGC 1068, supplemented by 55 pc resolution CO($J=1\text{-}0$) observations. We find that [CI] emission within the central kpc is strongly enhanced by a factor of $>$5 compared to the typical [CI]/CO intensity ratio of $\sim$0.2 for nearby starburst galaxies (in units of brightness temperature). The most [CI]-enhanced gas (ratio $>$ 1) exhibits a kpc-scale elongated structure centered at the AGN that matches the known biconical ionized gas outflow entraining molecular gas in the disk. A truncated, decelerating bicone model explains well the kinematics of the elongated structure, indicating that the [CI] enhancement is predominantly driven by the interaction between the ISM in the disk and the highly inclined ionized gas outflow (which is likely driven by the radio jet). Our results strongly favor the "CO dissociation scenario" rather than the "in-situ C formation" one which prefers a perfect bicone geometry. We suggest that the high [CI]/CO intensity ratio gas in NGC 1068 directly traces ISM in the disk that is currently dissociated and entrained by the jet and the outflow, i.e., the "negative" effect of the AGN feedback.