THE RADIO CONTINUUM STRUCTURE OF CENTAURUS A AT 1.4 GHz

Abstract

A 45 deg 2 radio continuum imaging campaign of the nearest radio galaxy, Centaurus A, is reported. Using the Australia Telescope Compact Array and the Parkes 64 m radio telescope at 1.4 GHz, the spatial resolution of the resultant image is ∼600 pc (∼ 50 ), resolving the 500 kpc giant radio lobes with approximately five times better physical resolution compared to any previous image, and making this the most detailed radio continuum image of any radio galaxy to date. In this paper, we present these new data and discuss briefly some of the most interesting morphological features that we have discovered in the images. The two giant outer lobes are highly structured and considerably distinct. The southern part of the giant northern lobe naturally extends out from the nothern middle lobe with uniformly north-streaming emission. The well known northern loop is resolved into a series of semi regular shells with a spacing of approximately 25 kpc. The northern part of the giant northern lobe also contains identifiable filaments and partial ring structures. As seen in previous single dish images at lower angular resolution, the giant southern lobe is not physically connected to the core at radio wavelengths. Almost the entirety of the giant southern lobe is resolved into a largely chaotic and mottled structure which appears considerably different (morphologically) to the diffuse regularity of the northern lobe. We report the discovery of a vertex and a vortex near the western boundary of the southern lobe; two striking, high surface-brightness features that are named based on their morphology and not their dynamics (which are presently unkown). The vortex and vertex are modelled as re-accelerated lobe emission due to shocks from the AGN itself or from the passage of a dwarf elliptical galaxy through lobe. Preliminary polarimetric and spectral index studies support a plasma reacceleration model and could explain the origin of the Faraday rotation structure detected in the southern lobe. In addition, there are a series of low surface brightness wisps detected around the edges of both the giant lobes.

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

“…ASCA did detect thermal emission from hot gas in a region associated with the northern giant lobe (Isobe et al 2001), and most recently, Stawarz et al (2013) have claimed thermal and non-thermal X-ray detection with Suzaku of parts of the southern giant lobe, though they do not detect inverseCompton emission. INTEGRAL hard X-ray observations of Cen A's giant lobes by Beckmann et al (2011) are consistent Feain et al 2011), showing the giant lobes and the vertex and vortex filaments. The jets, inner lobes and the northern middle lobe are located in the saturated region centred on the nucleus.…”

“…These sizes and volumes should be considered a lower limit, as the giant lobes may not lie perfectly in the plane of the sky. Feain et al (2011) have argued that the southern giant lobe is disconnected from the rest of the source and Stefan et al (2013) report a similar "gap" at 150 MHz, yet we cannot exclude the possibility that the southern lobe is in the process of detachment, or is fully connected. If the lobe were connected, the fainter region could be explained because the synchrotron emission is a non-linear tracer of the underlying plasma ( j sync ∝ U 2 e B 2 ), so that a small decrease in relativistic particles, magnetic field, or both can result in a large decrease in synchrotron brightness.…”

“…1), which are the brightest (in flux density) filamentary structures known in any radio galaxy. Their origin has been suggested by Feain et al (2011) to be due to enhanced core/jet activity of the parent AGN or the passage of the dwarf irregular galaxy KK 196, a Centaurus group member at 3.98 ± 0.29 Mpc (Karachentsev et al 2007), through the lobe.…”

Limiting magnetic fields in the cosmic web with diffuse radio emission

“…We therefore applied the Planck CMB mask (Planck Collaboration et al 2016) which masks out the Galactic plane and many of the brightest extragalactic point-sources. Residual emission remained due to the Galaxy and the bright extragalactic source Centaurus A (Feain et al 2011), so we further masked regions where the filtered S-PASS map was >0.1 Jy/beam. We have also masked out regions with extinction E(B-V)>0.1 from the Schlegel et al (1998) maps, as well as galactic latitudes |b| <10 degrees.…”

Fermi bubbles as a source of cosmic rays above 1015 eV

“…However some much more powerful objects with similar properties and probably similar nature are observed in some galaxies with active nuclei. For example even more giant structures are clearly seen in the direction of Cen-A in GHz radio [18,22], GeV [33] and TeV [3] gamma-ray ranges. Giant X-ray and radio lobes (bubbles) were found also in the galaxies NGC 3801 [16], Mrk 6 [27] and Circinus Galaxy [28].…”