59 research outputs found
Multiple merging events in the double cluster A3128/A3125
No full textJames A. Rose, Alejandro E. Gaba, Wayne A. Christiansen, David S. Davis, Nelson Caldwell, Richard W. Hunstead, and Melanie Johnston-Hollit
Revisiting the relativistic ejection event in XTE J1550-564 during the 1998 outburst
No full textWe revisit the discovery outburst of the X-ray transient XTE J1550−564 during which relativistic jets were observed in 1998 September, and review the radio images obtained with the Australian Long Baseline Array, and light curves obtained with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array. Based on Hi spectra, we constrain the source distance to between 3.3 and 4.9 kpc. The radio images, taken some 2 d apart, show the evolution of an ejection event. The apparent separation velocity of the two outermost ejecta is at least 1.3c and may be as large as 1.9c; when relativistic effects are taken into account, the inferred true velocity is ≥ 0.8c. The flux densities appear to peak simultaneously during the outburst, with a rather flat (although still optically thin) spectral index of −0.2
Quasars and radio galaxies
No full textRichard Hunstead is one of thirty-three Australian Science Citation Laureates whose papers have been most frequently cited by other scientists around the world. His discovery of variability in radio sources of low frequencies generated a large number of related research projects internationally. He also conducted a seminal study of the evolution of the so-called Lyman alpha absorption forest in distant quasars in the mid-1980s, pioneering observations of quasar absorption lines at high spectral resolution and measurement of the heavy-element enrichment of galaxies at high redshift. He has been leading an international team to find the first massive galaxies to form. This study will provide insights into the formation of galaxies in the early universe
0319 - 454: an FR II giant radio galaxy with twin jets
No full textWe present radio images of the edge-brightened giant radio galaxy 0319 – 454 made with the Australia Telescope at frequencies 1.5, 2.4 and 4.8 GHz. The observations show a jet and a counterjet out to exceptional distances of 380 and 590 kpc, respectively, from the radio core. 0319–454 is therefore one of only three powerful radio galaxies observed to date to have twin quasi-continuous jets. The NE lobe of the double radio structure has an extremely rare configuration of five compact hotspots that may be classified into a primary and a cluster of four secondaries. Optical imaging of the parent galaxy reveals a prominent, warped dust lane and a highly disturbed structure that is indicative of past merger activity
Episodic ejection from super-massive black holes
No full textEpisodic activity in super-massive black holes is shown by radio galaxies exhibiting ‘double-double’ radio morphologies (Subrahmanyan et al. 1996, Schoenmakers et al. 2000). Spectacular examples showing a renewal of beam activity in the form of new beams emerging within relic radio lobes of previous activity have placed the phenomenon of recurrence in AGN outflows on a firm footing. By using the SUMSS and WENSS GRG samples, we infer that on timescales of order a few million years, low luminosity radio sources are more likely to exhibit episodic behaviour in the accretion on to their supermassive black holes as compared to the more powerful radio galaxies
Morphologies in megaparsec-size powerful radio galaxies
No full textWe present radio images with the Australia Telescope of a sample of powerful radio galaxies. The observations were designed to be sensitive to the largest-scale structures in the radio sources. The morphologies are representative of radio galaxies with FRII type structures and with sizes exceeding 1 Mpc. We observe the giant sources to have the same axial ratios as those in smaller sources with similar radio powers. Moreover, the deviations from axial symmetry are also observed to be linearly scaled from sources an order of magnitude smaller. The observations are indicative of self-similar evolution in the morphologies of powerful radio galaxies
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