Impact of AGN and nuclear star formation on the ISM turbulence of galaxies: Insights from JWST/MIRI spectroscopy

TL;DR

The paper analyzes JWST/MIRI/MRS spectroscopy of 54 nearby galaxies to investigate the origin of turbulence in the warm molecular and low-/mid-ionization gas within the inner few kiloparsecs, comparing AGN hosts and star-forming systems. By measuring fluxes and $W_{80}$ for H$_2$ S(5), [Ar II], [Fe II], [Ar III], and [Mg V], and confronting results with shock (MAPPINGS V) and photoionization (Cloudy) models, the authors demonstrate that shocks from AGN outflows, jets, and stellar winds markedly enhance turbulence, particularly in ionized and coronal gas, while H$_2$ often traces post-shock molecular gas. The study finds that $W_{80}$ generally increases with radius for multiple tracers and correlates with shock-sensitive line ratios, supporting a scenario where AGN and stellar feedback drive ISM turbulence and heating, influencing gas cooling and star formation. These findings highlight the significance of multi-phase, shock-mediated feedback in galaxy evolution and showcase JWST's capability to spatially resolve turbulence in obscured nuclear regions. The work provides a framework for interpreting AGN feedback as a maintenance mechanism that sustains turbulence and regulates star formation across varied environments.

Abstract

Active galactic nuclei (AGN), star formation (SF), and galaxy interactions can drive turbulence in the gas of the ISM, which in turn plays a role in the SF within galaxies. The impact on molecular gas is of particular importance, as it serves as the primary fuel for SF. Our goal is to investigate the origin of turbulence and the emission of molecular gas, as well as low- and intermediate-ionization gas, in the inner few kpc of both AGN hosts and SF galaxies. We use JWST MIRI/MRS observations of a sample consisting of 54 galaxies at z<0.1. We present fluxes of the H2 S(5)6.9091, [Ar II]6.9853, [FeII]5.3403, and [Ar III]8.9914 lines, along with velocity dispersion from W80. For galaxies with coronal emission, [Mg V]5.6098 is also included. Line ratios are compared to photoionization and shock models to explore the origin of the gas emission. AGNs exhibit broader emission lines than SFGs, with the largest velocity dispersions observed in radio-strong (RS) AGNs. H2 gas is less turbulent compared to ionized gas, while coronal gas presents higher velocity dispersions. The W80 values for the ionized gas exhibits a decrease from the nucleus out to radii of approximately 0.5--1 kpc, followed by an outward increase up to 2-3 kpc. In contrast, the H2 line widths generally display increasing profiles with distance from the center. Correlations W80 and line ratios such as H2 S(5)/[ArII] and [FeII]/[ArII] indicate that the most turbulent gas is associated with shocks, enhancing H2 and [FeII] emissions. We speculate that these shocked gas regions are produced by AGN outflows and jet-cloud interactions in AGN-dominated sources, while in SFGs, they may be created by stellar winds and mergers. This shock-induced gas heating may be an important mechanism of AGN (or stellar) feedback, preventing the gas from cooling and forming new stars.

Figures (10)

• Figure 1: Venn diagram illustrating the overlap among the different AGN subsamples.
• Figure 2: WISE color–color diagram showing the five subsamples, as indicated by the symbols. The uncertainties are comparable to the symbol sizes. The large symbols with error bars correspond to the mean values for each subsample, with the error bars representing the standard deviation. The dashed line represents the threshold $W1-W2 = 0.8$, while the dotted polygon marks the region typically occupied by Seyfert galaxies Jarrett11.
• Figure 3: Examples of flux (top panels) and $W_{\rm 80}$ (bottom panels) maps for Arp 220. From left to right, the H$_2$ S(5)$\lambda6.9091\mu$m, [Ar ii]$\lambda6.9853\mu$m, [Fe ii]$\lambda5.3403\mu$m, and [Ar iii]$\lambda8.9914\mu$m are shown. The central crosses identify the location of the peak of the continuum, corresponting to the western nucleus, used as reference to calculate radial distances from the galaxy nucleus. The gray regions correspond to locations where the corresponding emission line is not detected with $snr > 5$ and regions not covered by the MRS FoV.
• Figure 4: Nuclear $W_{\rm 80}$ values for the H$_2$ S(5), [Fe ii], [Ar ii], and [Ar iii] emission lines — ordered by increasing ionization potential from top to bottom — are shown for the five subsamples, displayed in separate columns. The $W_{\rm 80}$ values are estimated as the flux weighted mean $W_{\rm 80}$ values of spaxels within a radius of 0.5 arcsec centered at the peak or the continuum emission. The mean values (indicated by vertical dotted lines), standard error, and the number of galaxies are displayed in each panel.
• Figure 5: Radial $W_{\rm 80}$ profiles for H$_2$ (top left), [Fe ii] (top right), [Ar ii] (bottom left) and [Ar iii] (bottom right) for the five subsamples, as indicated by the different colors. These profiles are computed as median values of $W_{\rm 80}$ and distance of the spaxel from the position of the continuum peak, within circular rings of 250 pc width. The numbers next to each point indicate the number of galaxies used to compute it, and the shaded regions represent the range between the 25th and 75th percentiles of the $W_{\rm 80}$ values within each radial bin, illustrating the spread of values observed in each emission line