The giant lobes of Centaurus A observed at 118 MHz with the Murchison Widefield Array

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

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Event Horizon Telescope observations of the jet launching and collimation in Centaurus A

Nature Astronomy ◽

10.1038/s41550-021-01417-w ◽

2021 ◽

Author(s):

Michael Janssen ◽

Heino Falcke ◽

Matthias Kadler ◽

Eduardo Ros ◽

Maciek Wielgus ◽

...

Keyword(s):

Black Holes ◽

Event Horizon ◽

Galactic Nuclei ◽

Galactic Centre ◽

Radio Jets ◽

Long Baseline ◽

Wide Range ◽

Terahertz Frequencies ◽

Source Structure ◽

Centaurus A

AbstractVery-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg ≡ GM/c2) scales in nearby sources1. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on ~500 rg scales remarkably well. Furthermore, we identify the location of Centaurus A’s SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source’s event horizon shadow4 should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses5,6.

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Filaments in the southern giant lobe of Centaurus A: constraints on nature and origin from modelling and GMRT observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stu1033 ◽

2014 ◽

Vol 442 (4) ◽

pp. 2867-2882 ◽

Cited By ~ 11

Author(s):

Sarka Wykes ◽

Huib T. Intema ◽

Martin J. Hardcastle ◽

Abraham Achterberg ◽

Thomas W. Jones ◽

...

Keyword(s):

Centaurus A

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GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey III: South Galactic Pole data release

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.5 ◽

2021 ◽

Vol 38 ◽

Author(s):

T. M. O. Franzen ◽

N. Hurley-Walker ◽

S. V. White ◽

P. J. Hancock ◽

N. Seymour ◽

...

Keyword(s):

Large Scale ◽

Angular Resolution ◽

Beam Model ◽

Spectral Variability ◽

Extragalactic Source ◽

Automated Algorithm ◽

Data Release ◽

Murchison Widefield Array ◽

Source Populations ◽

One Year

Abstract We present the South Galactic Pole (SGP) data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. These data combine both years of GLEAM observations at 72–231 MHz conducted with the Murchison Widefield Array (MWA) and cover an area of 5 113 $\mathrm{deg}^{2}$ centred on the SGP at $20^{\mathrm{h}} 40^{\mathrm{m}} < \mathrm{RA} < 05^{\mathrm{h}} 04^{\mathrm{m}}$ and $-48^{\circ} < \mathrm{Dec} < -2^{\circ} $ . At 216 MHz, the typical rms noise is ${\approx}5$ mJy beam–1 and the angular resolution ${\approx}2$ arcmin. The source catalogue contains a total of 108 851 components above $5\sigma$ , of which 77% have measured spectral indices between 72 and 231 MHz. Improvements to the data reduction in this release include the use of the GLEAM Extragalactic catalogue as a sky model to calibrate the data, a more efficient and automated algorithm to deconvolve the snapshot images, and a more accurate primary beam model to correct the flux scale. This data release enables more sensitive large-scale studies of extragalactic source populations as well as spectral variability studies on a one-year timescale.

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