[Paper Review] Multi-scale feedback and feeding in the closest radio galaxy Centaurus A

B. McKinley, S. J. Tingay+13 more|arXiv (Cornell University)|Nov 4, 2021

Galaxies: Formation, Evolution, Phenomena4 citations

TL;DR

This study presents low-frequency radio observations from the Murchison Widefield Array that reveal a broad, bipolar outflow at 1100 km s⁻¹ and a mass outflow rate of 2.9 M☉ yr⁻¹ in Centaurus A, spanning 10–100 kpc scales. The findings support the Chaotic Cold Accretion (CCA) model, unifying feedback and feeding across multi-scale, multi-wavelength data, demonstrating large-scale mechanical feedback consistent with self-regulated AGN activity.

ABSTRACT

Supermassive black holes and supernovae explosions at the centres of active galaxies power cycles of outflowing and inflowing gas that affect galactic evolution and the overall structure of the Universe. While simulations and observations show that this must be the case, the range of physical scales (over ten orders of magnitude) and paucity of available tracers, make both the simulation and observation of these effects difficult. By serendipity, there lies an active galaxy, Centaurus A (NGC 5128), at such a close proximity as to allow its observation over this entire range of scales and across the entire electromagnetic spectrum. In the radio band, however, details on scales of 10-100 kpc from the supermassive black hole have so far been obscured by instrumental limitations. Here we report low-frequency radio observations that overcome these limitations and show evidence for a broad, bipolar outflow with velocity 1100 km per s and mass outflow rate of 2.9 solar masses per year on these scales. We combine our data with the plethora of multi-scale, multi-wavelength historical observations of Centaurus A to probe a unified view of feeding and feedback, which we show to be consistent with the Chaotic Cold Accretion self-regulation scenario.

Motivation & Objective

• To resolve the multi-scale feedback and feeding processes in Centaurus A across 10–100 kpc scales, which are obscured by instrumental limitations in previous radio observations.
• To investigate the physical mechanisms linking AGN outflows and inflows in a nearby radio galaxy, using a unified model of active galactic nucleus (AGN) feedback and accretion.
• To test the Chaotic Cold Accretion (CCA) scenario as a self-regulating mechanism for AGN feedback by combining low-frequency radio data with multi-wavelength observations.
• To reveal previously unseen radio structures—particularly in the northern and southern transition regions—using high dynamic range, widefield imaging.
• To establish a consistent, multi-scale view of energy and mass transfer in Centaurus A, linking hot plasma cooling, multiphase condensation, and large-scale outflows.

Proposed method

• Utilized low-frequency (185 MHz) radio observations from the Murchison Widefield Array (MWA), leveraging its wide field-of-view and sensitivity to large angular scales.
• Applied advanced imaging techniques to produce high-dynamic-range, artifact-free radio images of Centaurus A at 1.5 × 1.2 arcmin resolution, revealing diffuse filaments and flattened radio knots.
• Combined MWA radio data with existing multi-wavelength datasets: HI gas (from Arecibo), Hα and FUV emission (from CFHT), X-ray emission (from Chandra), and optical stellar maps.
• Performed spatial and spectral cross-matching of radio, X-ray, Hα, and HI features to identify co-spatial structures indicative of multi-phase gas interactions.
• Used the Chaotic Cold Accretion (CCA) model as a theoretical framework to interpret the observed multi-scale feedback and inflow dynamics.
• Conducted statistical and morphological analysis of radio structures (e.g., arcing filaments, flattened knots) to infer magnetic field alignment and outflow kinematics.

Experimental results

Research questions

• RQ1 What is the nature and extent of large-scale outflows in Centaurus A at 10–100 kpc scales, and how do they relate to the central AGN activity?
• RQ2 How do the observed radio structures in the northern and southern transition regions correlate with multi-phase gas (HI, Hα, X-ray) and support the CCA feedback model?
• RQ3 To what extent do the observed feedback and inflow features in Centaurus A align with predictions of the Chaotic Cold Accretion (CCA) scenario?
• RQ4 What is the mass outflow rate and velocity of the large-scale bipolar outflow, and how does it compare to theoretical expectations?
• RQ5 Can the unified CCA model reconcile the observed multi-scale, multi-wavelength features of feedback and feeding in a nearby radio galaxy?

Key findings

• The MWA detected a broad, bipolar outflow extending over 10–100 kpc with a velocity of 1100 km s⁻¹ and a mass outflow rate of 2.9 M☉ yr⁻¹, confirming large-scale mechanical feedback.
• Previously unseen radio filaments and flattened radio knots were revealed in the northern transition region, aligned with magnetic field directions and associated with Hα and X-ray emission.
• The northern transition region exhibits co-spatial features across radio, Hα, X-ray, and HI bands, indicating ongoing multi-phase gas interactions consistent with the CCA model.
• The southern transition region shows a prominent radio arc at 500 mJy/beam, suggesting similar feedback processes on the opposite side of the nucleus.
• The multi-scale, multi-wavelength data set supports the Chaotic Cold Accretion (CCA) scenario, where cooling hot plasma condenses into multi-phase clouds that rain inward while outflows entrain mass and deposit energy.
• The observed feedback and inflow processes are consistent with a self-regulated system where AGN outflows quench cooling flows, as predicted by the CCA model.