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Abstract:

ABSTRACT Broad-band mid-infrared (MIR) imaging with high-spatial resolution is useful to study extended dust structures in the circumnuclear regions of nearby active galactic nuclei. However, broad-band imaging filters cannot distinguish dust continuum emission from emission lines, and so accounting for the emission line contamination becomes crucial in studying extended dust in these environments. This paper uses Cycle 1 MIR imaging from the James Webb Space Telescope's Mid-Infrared Instrument (JWST/MIRI) and spectroscopy from the Medium-Resolution Spectrometer (JWST/MRS) for 11 local Seyfert galaxies, as part of the Galactic Activity, Torus and Outflow Survey (GATOS). Three of the objects (NGC 3081, NGC 5728, and NGC 7172) exist in both data sets, allowing direct measurement of the line emission using the spectroscopy for these objects. We find that extended MIR emission persists on scales of 100 s of parsecs after the removal of contamination from emission lines. Further, the line contamination levels vary greatly between objects (from 5 per cent to 30 per cent in the F1000W filter), and across filters, so cannot be generalized across a sample and must be carefully treated for each object and band. We also test methods to estimate the line contamination when only MRS spectroscopy or MIRI imaging is available, using pre-JWST ancillary data. We find that these methods estimate the contamination within 10 percentage points. This paper serves as a useful guide for methods to quantify and mitigate for emission line contamination in MIRI broad-band imaging.

Abstract:

Current co-evolutionary models of galaxies and their supermassive black holes (SMBHs) almost unanimously predict the existence of a heavily dust-obscured nuclear phase, critical in growing the SMBH and providing feedback to the host galaxy. However, this phase is poorly understood. Compact obscured nuclei (CONs) are relatively common in local (ultra-)luminous infrared galaxies and are the most obscured nuclei known to date, offering the opportunity to study the effects of such a dust-obscured phase on the galaxy. This work presents a case study of the local CON Zw049.057; we study the large-scale features of the galaxy and their connection to the ongoing activity of the central CON. We present new, targeted MUSE observations of the local CON galaxy Zw049.057, which is known to host multiple outflow features within its central few hundred parsecs. By mapping the kinematics of Hα, we analysed the large-scale features of the galaxy. For the first time, we identify a kiloparsec-scale ionised outflow in Zw049.057, traced by Hα emission. Kinematics reveal the outflow to be blueshifted and orientated to the foreground of the stellar disk. The ionisation of this outflow is consistent with shock-heating, which may be related to the presence of a previously identified radio jet in the galaxy.

Abstract:

We present JWST/MIRI spectra from the Medium-Resolution Spectrometer of I Zw 18, a nearby dwarf galaxy with a metallicity of ∼3% solar. Its proximity enables a detailed study of highly ionized gas that can be interpreted in the context of newly discovered high-redshift dwarf galaxies. We derive aperture spectra centered on 11 regions of interest; the spectra show very low extinction, AV ≲ 0.1, consistent with optical determinations. The gas is highly ionized; we have detected 10 fine-structure lines, including [O iv] 25.9 μm with an ionization potential (IP) of ∼55 eV, and [Ne v] 14.3 μm with an IP of ∼97 eV. The ionization state of I Zw 18 falls at the extreme upper end of all of the line ratios we analyzed, but not coincident with galaxies containing an accreting massive black hole (active galactic nucleus). Comparison of the line ratios with state-of-the-art photoionization and shock models suggests that the high-ionization state in I Zw 18 is not due to shocks. Rather, it can be attributed to metal-poor stellar populations with a self-consistent contribution of X-ray binaries or ultra-luminous X-ray sources. It could also be partially due to a small number of hot low-metallicity Wolf−Rayet stars ionizing the gas; a small fraction (a few percent) of the ionization could come from an intermediate-mass black hole. Our spectroscopy also revealed four 14 μm continuum sources, ≳30–100 pc in diameter, three of which were not previously identified. Their properties are consistent with H ii regions ionized by young star clusters.