[Paper Review] AGN-host interaction in IC 5063. I. Large-scale X-ray morphology and spectral analysis

A. Travascio, G. Fabbiano+6 more|arXiv (Cornell University)|Jul 26, 2021

Astrophysical Phenomena and Observations117 references25 citations

TL;DR

This study presents deep Chandra X-ray observations of the radio-loud Seyfert 2 galaxy IC 5063, revealing extended soft X-ray emission along the bi-cone and jet directions, with spectral analysis indicating jet-ISM interaction as the dominant driver of hot gas emission. Key findings include spatially extended Fe Kα and Fe XXV emission correlated with radio hotspots, indicating shock ionization, and a highly clumpy, low-density plasma in the cross-cone region consistent with lateral outflows driven by radio jet feedback.

ABSTRACT

We report the analysis of the deep (270 ks) X-ray Chandra data of one of the most radio-loud, Seyfert 2 galaxies in the nearby Universe (z=0.01135), IC 5063. The alignment of the radio structure with the galactic disk and ionized bi-cone, enables us to study the effects of both radio jet and nuclear irradiation on the interstellar medium (ISM). The nuclear and bi-cone spectra suggest a low photoionization phase mixed with a more ionized or thermal gas component, while the cross-cone spectrum is dominated by shocked and collisionally ionized gas emission. The clumpy morphology of the soft (<3 keV) X-ray emission along the jet trails, and the large (~2.4 kpc) filamentary structure perpendicular to the radio jets at softer energies (<1.5 keV), suggest a large contribution of the jet-ISM interaction to the circumnuclear gas emission. The hard X-ray continuum (>3 keV) and the Fe K-alpha 6.4 keV emission are both extended to kpc size along the bi-cone direction, suggesting an interaction of nuclear photons with dense clouds in the galaxy disk, as observed in other Compton Thick (CT) active nuclei. The north-west cone spectrum also exhibits an Fe XXV emission line, which appears spatially extended and spatially correlated with the most intense radio hot-spot, suggesting jet-ISM interaction.

Motivation & Objective

• To investigate the large-scale X-ray morphology and spectral properties of hot gas in IC 5063, a nearby radio-loud Seyfert 2 galaxy.
• To disentangle the contributions of nuclear radiation, radio jets, and outflows to the extended X-ray emission.
• To determine the physical conditions (ionization, temperature, density) of the circumnuclear gas through spatially resolved spectral analysis.
• To assess the role of jet-ISM interaction in triggering and shaping multi-phase outflows in a Compton-thick AGN environment.
• To test feedback models by comparing X-ray morphology and spectra with multi-wavelength observations and simulations.

Proposed method

• Performed deep (272 ks) Chandra ACIS-S X-ray observations combining archival and new data, with background flare removal using sigma-clipping.
• Conducted spatial analysis across multiple energy bands (soft <3 keV, hard 3–6 keV, <1.5 keV) to map extended emission morphology.
• Extracted spatially resolved spectra from nuclear, bi-cone, and cross-cone regions for spectral fitting using XSPEC and CLOUDY models.
• Modelled the nuclear spectrum with a reprocessed continuum, leaky absorber (covering fraction ≈99.2%), and soft excess via photoionized or thermal components.
• Fitted extended emission spectra with combinations of photoionized, collisionally ionized, and shock ionized gas models to determine ionization state and temperature.
• Used filling factor estimates (η < 0.01) to infer clumpiness of the hot plasma, comparing with CO gas observations and simulations.

Experimental results

Research questions

• RQ1 What is the spatial distribution of soft and hard X-ray emission in IC 5063, and how does it correlate with radio jets and ionization cones?
• RQ2 What physical processes (photoionization, shock, thermal emission) dominate the X-ray emission in the extended bi-cone and cross-cone regions?
• RQ3 Is the Fe Kα 6.4 keV line emission spatially correlated with radio hotspots, and what does this imply about reprocessing by dense clouds?
• RQ4 What is the ionization state and electron density of the hot plasma in the cross-cone region, and how does it compare to simulations and other AGNs?
• RQ5 To what extent does jet-ISM interaction drive multi-phase outflows, as indicated by X-ray, optical, and radio data?

Key findings

• The soft X-ray emission (<3 keV) is extended up to ∼3.5 kpc along the bi-cone and jet direction, with morphology strongly correlated with the radio jet structure, indicating jet-ISM interaction as the primary driver.
• The nuclear spectrum shows a hard continuum with a 6.4 keV Fe Kα line and a soft excess, best fit by a reprocessed continuum with a leaky absorber (covering fraction 99.2 ± 0.2%) and a high-density, low-ionization photoionized component mixed with a more ionized or thermal component (kT ∼1–3 keV).
• The hard X-ray continuum (>3 keV) is extended along the bi-cone, with a steeper photon index (Γ ≈ 2.7) than the nuclear component (Γ ≈ 1.5), indicating reprocessing in distant, dense clouds.
• A broad feature at 6.1–6.6 keV and spatially extended Fe XXV emission are detected in the NW cone, spatially correlated with the brightest radio hot-spot, indicating shock ionization from jet-ISM interaction.
• The soft X-ray emission at <1.5 keV in the cross-cone region (perpendicular to jets) is extended over ∼3 kpc and best fit by a mix of highly ionized photoionized gas (logU ∼0.8–1.8) or thermal plasma (kT ∼0.3–2 keV), consistent with lateral outflows.
• Electron densities in the cross-cone region are estimated at ne ∼0.1–0.3 cm⁻³, implying a filling factor η < 0.01, indicating a highly clumpy, porous medium consistent with simulations and CO observations.