Stratification of the AGN-Driven multi-phase outflows in the dwarf Seyfert galaxy NGC 4395

TL;DR

This study uses multi-wavelength spectroscopy to analyze the multi-phase outflows driven by the AGN in NGC 4395, revealing stratified velocities, diverse gas phases, and their impact on the galaxy's interstellar medium.

Contribution

It provides a detailed multi-phase, multi-wavelength characterization of AGN-driven outflows in a dwarf galaxy, highlighting the stratification and efficiency of different gas phases.

Findings

Cold molecular outflow rate exceeds warm/hot phases by 1-2 orders of magnitude.

Outflow velocities range from 127 to 716 km/s, with stratified geometry.

Low-ionisation gas has a significant impact on the ISM.

Abstract

We present a multi-wavelength study of nuclear outflows in the nearby dwarf Seyfert galaxy NGC~4395, which hosts an intermediate-mass black hole. Using \textit{JWST}/NIRSpec and MIRI IFU spectroscopy (1.66--28.6~$\mu$m), together with ALMA and Gemini/GMOS data, we probe the ionised and molecular gas on parsec scales. The JWST nuclear spectra reveal 134 emission lines, including H\,\textsc{i}, He, numerous fine-structure lines, H$_2$ rotational/ro-vibrational transitions, and several PAH bands. Modelling of the H$_2$ rotational lines reveals three warm/hot molecular components ($T\!\approx\!580$, 1480, and 2900~K), along with a cold ($<50$~K) phase traced by ALMA CO(2--1). Outflow signatures are detected in cold and warm/hot molecular gas, in H\,\textsc{i}, and in 36 fine-structure lines spanning ionisation potentials of 7.6--300~eV. Ionised outflow velocities range from 127 to 716~km\,s$^{-1}$, with blueshifted and redshifted components consistent with a stratified biconical geometry. The cold molecular gas shows a mass outflow rate nearly 1--2 orders of magnitude larger than that of the warm/hot molecular and ionised phases. The kinetic coupling efficiency is 0.003--0.12\% for the coronal-line gas and 0.4--1.4\% for the H\,\textsc{i} outflow, indicating that only the low-ionisation gas significantly impacts the surrounding ISM. Outflow velocity and the fraction of flux in the outflowing component increase with ionisation potential, implying that the most highly ionised gas originates closest to the AGN and is most efficiently accelerated.