Probing AGN Feedback in Dwarf Galaxies with Spatially Resolved NIR Coronal Lines from JWST

TL;DR

This paper presents the first spatially resolved JWST/NIRSpec study of near-infrared coronal lines in four dwarf galaxies hosting AGN and ionized outflows. By mapping 16 CL species across 0.5 kpc scales and performing robust ionization diagnostics, the authors show that AGN photoionization dominates CL excitation and that the coronal line region can occupy up to ~10% of a dwarf galaxy’s size, correlating with [O III] outflow properties. The results reveal biconical, AGN-driven CLR structures, occasional broad CL components signaling outflows in highly ionized gas, and energetics where CL-based outflows can significantly perturb central gas despite their compactness. Collectively, the findings provide strong evidence that AGN in low-mass galaxies can drive meaningful feedback, influencing the central gas distribution and potentially shaping dwarf galaxy evolution, with implications for understanding black hole growth and reionization-era analogs in the early universe.

Abstract

We present the first spatially resolved investigation of near-infrared coronal lines in dwarf galaxies hosting active galactic nuclei (AGN), using JWST/NIRSpec integral field spectroscopy. Coronal lines (CLs), which are forbidden transitions from highly ionized species with ionization potentials up to 450 eV, act as sensitive tracers of the AGN ionizing continuum and feedback processes. Across four dwarf galaxies with ionized gas outflows traced by the optical [O III] lines, we report the detection of 16 unique species of near-infrared CLs. Line ratio diagnostics indicate that photoionization from the AGN dominates the excitation of CLs. We find that the coronal line region in dwarf galaxies, traced by the various CLs, extends up to 0.5 kpc, and can constitute up to 10% of their host galaxy size. Correlations between CL luminosities and [O III] ionized gas outflow properties are consistent with a scenario in which AGN-driven outflows likely facilitate the detection of CLs and contribute to their extent. Several CLs, including [Si VI], [Si VII], and [Mg VIII], exhibit a secondary broad component (W$_{80}$ > 300 km/s). If we interpret this spatially compact gas as part of an outflow, this would indicate that the outflowing gas includes a wide range of ionizations. The estimated energetics imply this highly ionized component is compact yet powerful enough to perturb gas in the central regions of the host dwarfs. These results indicate that AGN in low-mass galaxies may produce outflows capable of influencing their structure and evolution.

Figures (16)

• Figure 1: Keck/KCWI spectrum of J0906, one of the targets in the sample, showing the blue-shifted wings of [O III] within the central 0.5 kpc. All the targets observed with JWST exhibit similar ionized gas outflow profiles detected in [O III].
• Figure 2: Examples of (a) one Gaussian component and (b) two Gaussian components fit to the [Si VI] line profile for J0954 for the same single spaxel. In each panel, the black spectrum is the observed data, the solid red line is the best fit, and the blue lines represent the Gaussian components. The residuals after subtraction from the best fit are shown at the bottom of each panel. We see that the single component in (a) does not adequately fit the observed line profile; based on the F-test and CHI2RATIO test, a second component is justified. A similar second component was also required in the central spaxels of [Si VII], [Si IX], [Mg IV], [Mg VIII] and [Ar VI] lines in J0954 and J1009.
• Figure 3: Flux, v$_{\mathrm{off}}$ and W$_{80}$ maps of the narrow component for select CLs in J1009, in order of increasing I.P. The axes represent the physical scale in kpc. The magenta contours indicate the galaxy continuum, and we find that the CLs tend to be oriented perpendicular to the major axis of the galaxy continuum. The magenta and green crosses indicate the peak of the continuum flux and the potential AGN location (the slight ($\sim$1 pixel) mismatch in the peak can be attributed to PSF wandering between the different NIRSpec filters). The maps are oriented with North pointing up and East to the left.
• Figure 4: Flux, v$_{\mathrm{off}}$ and W$_{80}$ maps, showing the two components in the [Si VI] line in J0954. The magenta contours trace the galaxy continuum and the cross indicates the peak continuum flux corresponding to the AGN position. The detected second component (bottom panel) across all the lines is found to be more compact than the first component, is concentrated in the central region and has larger W$_{80}$ values than the first component.
• Figure 5: Zoomed-in spectra taken from a 0.3$\arcsec$ radius aperture centered on the galaxy nucleus showing the detected ($>$3$\sigma$; green dotted lines) CLs in the four targets. The non-detections are indicated by the red dotted lines. Although in certain panels, there may be features that are indicative of CL lines, we only claim a detection if the line is $>$3$\sigma$ above the noise. The continuum flux is normalized to unity and the systemic redshift was used to shift the spectra to rest-frame wavelength. The JWST/NIRSpec detector gaps are indicated by the gray shaded region.