Stratification of the active galactic nucleus─driven multiphase outflows in the dwarf Seyfert galaxy NGC 4395

Abstract

We present a multiwavelength study of nuclear outflows in the nearby dwarf Seyfert galaxy NGC 4395, which hosts an intermediate-mass black hole. Using JWST/NIRSpec and MIRI integral-field-unit spectroscopy (1.66–28.6 μm), together with Atacama Large Millimeter/submillimeter Array (ALMA) and Gemini/GMOS data, we probe the ionized and molecular gas on parsec scales. The JWST nuclear spectra reveal 134 emission lines, including H I, He, numerous fine-structure lines, H2 rotational/rovibrational transitions, and several polycyclic aromatic hydrocarbon bands. Modelling of the H2 rotational lines reveals three warm/hot molecular components (T ≈ 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 I, and in 36 fine-structure lines spanning ionization potentials of 7.6–300 eV. Ionized 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 ionized phases. The kinetic coupling efficiency is 0.003%–0.12% for the coronal-line gas and 0.4%–1.4% for the H I outflow, indicating that only the low-ionization gas significantly impacts the surrounding ISM. Outflow velocity and the fraction of flux in the outflowing component increase with ionization potential, implying that the most highly ionized gas originates closest to the active galactic nucleus and is most efficiently accelerated.