Australia Telescope National Facility

About: Australia Telescope National Facility is a facility organization based out in Sydney, New South Wales, Australia. It is known for research contribution in the topics: Galaxy & Pulsar. The organization has 699 authors who have published 2774 publications receiving 151507 citations. The organization is also known as: ATNF.

Seyfert galaxies and the radio—far-infrared correlation

Abstract: We have observed a sample of 149 Seyfert galaxies and radio-quiet quasars at 13 cm with both a 275-km radio interferometer and the 6-km compact array of the Australia Telescope The high-resolution observations searched for the presence of compact, high-brightness-temperature radio emission from the active nucleus The low-resolution observations measured the total radio emission from the galaxy disc and Seyfert core and lobes From these we draw the following conclusions (i) Seyfert galaxies that lack compact radio cores display a correlation between radio and far-infrared (FIR) emission similar to the correlation displayed by normal spirals, albeit with greater scatter The correlation is found to be intrinsic and is not an artefact of the richness effect (ii) A very different radio–FIR correlation is displayed by those Seyferts that harbour compact radio cores These tend to be more radio-loud than either normal spirals or the Seyferts that lack compact cores The compact core emission thus seems to be responsible for the generally poor radio–FIR correlation displayed by Seyfert galaxies (iii) The radio–FIR correlation is not significantly improved by subtracting off the 01-arcsec (20- to 200-pc) compact radio emission from the total radio emission This suggests that the emission from the active galactic nucleus has significant structure on scales larger than 01 arcsec Perhaps these structures are the ‘linear’ radio features that have been seen previously in Seyfert nuclei

The ATCA intraday variability survey of extragalactic radio sources

Abstract: We present the results of an Australia Telescope Compact Array (ATCA) survey for intra-day variability (IDV) of the total and polarized flux densities of 118 compact, flat spectrum, extragalactic radio sources from the Parkes 2.7 GHz Survey. A total of 22 total flux density IDV sources were discovered and 15 sources were found to show IDV of their polarized flux density. We discuss the statistical properties of the IDV sources, including the distribution of source modulation indices, and the dependence of the variability amplitude on source spectral index and on Galactic position. We suggest interstellar scintillation (ISS) in the Galactic interstellar medium as the most likely mechanism for IDV. Even so, the inferred high brightness temperatures cannot be easily explained.

Multifrequency radio measurements of supernova 1987a over 22 years

Abstract: We present extensive observations of the radio emission from the remnant of supernova (SN) 1987A made with the Australia Telescope Compact Array (ATCA), since the first detection of the remnant in 1990. The radio emission has evolved in time providing unique information on the interaction of the SN shock with the circumstellar medium. We particularly focus on the monitoring observations at 1.4, 2.4, 4.8, and 8.6 GHz, which have been made at intervals of 4-6 weeks. The flux density data show that the remnant brightness is now increasing exponentially, while the radio spectrum is flattening. The current spectral index value of –0.68 represents an 18 ± 3% increase over the last eight years. The exponential trend in the flux is also found in the ATCA imaging observations at 9 GHz, which have been made since 1992, approximately twice a year, as well as in the 843 MHz data set from the Molonglo Observatory Synthesis Telescope from 1987 to 2007 March. Comparisons with data at different wavelengths (X-ray, Hα) are made. The rich data set that has been assembled in the last 22 years forms a basis for a better understanding of the evolution of the supernova remnant.

Green bank telescope studies of giant pulses from millisecond pulsars

Abstract: We have conducted a search for giant pulses from four millisecond pulsars using the 100 m Green Bank Telescope. Coherently dedispersed time series from PSR J0218+4232 were found to contain giant pulses of very short intrinsic duration whose energies follow power-law statistics. The giant pulses are in phase with the two minima of the radio integrated pulse profile but are phase-aligned with the peaks of the X-ray profile. Historically, individual pulses more than 10-20 times the mean pulse energy have been deemed to be "giant pulses." As only 4 of the 155 pulses had energies greater than 10 times the mean pulse energy, we argue the emission mechanism responsible for giant pulses should instead be defined through: (1) intrinsic timescales of microsecond or nanosecond duration; (2) power-law energy statistics; and (3) emission occurring in narrow phase windows coincident with the phase windows of nonthermal X-ray emission. Four short-duration pulses with giant-pulse characteristics were also observed from PSR B1957+20. As the inferred magnetic fields at the light cylinders of the millisecond pulsars that emit giant pulses are all very high, this parameter has previously been considered to be an indicator of giant-pulse emissivity. However, the frequency of giant-pulse emission from PSR B1957+20 is significantly lower than for other millisecond pulsars that have similar magnetic fields at their light cylinders. This suggests that the inferred magnetic field at the light cylinder is a poor indicator of the rate of emission of giant pulses.

The ATLAS3D project - XXVI : H I discs in real and simulated fast and slow rotators

Abstract: One quarter of all nearby early-type galaxies (ETGs) outside Virgo host a disc/ring of H i with size from a few to tens of kpc and mass up to ∼10^9 M_⊙. Here we investigate whether this H i is related to the presence of a stellar disc within the host making use of the classification of ETGs in fast and slow rotators (FR/SR). We find a large diversity of H i masses and morphologies within both families. Surprisingly, SRs are detected as often, host as much H i and have a similar rate of H i discs/rings as FRs. Accretion of H i is therefore not always linked to the growth of an inner stellar disc. The weak relation between H i and stellar disc is confirmed by their frequent kinematical misalignment in FRs, including cases of polar and counterrotating gas. In SRs the H i is usually polar. This complex picture highlights a diversity of ETG formation histories which may be lost in the relative simplicity of their inner structure and emerges when studying their outer regions. We find that Λ CDM hydrodynamical simulations have difficulties reproducing the H i properties of ETGs. The gas discs formed in simulations are either too massive or too small depending on the star formation feedback implementation. Kinematical misalignments match the observations only qualitatively. The main point of conflict is that nearly all simulated FRs and a large fraction of all simulated SRs host corotating H i. This establishes the H i properties of ETGs as a novel challenge to simulations.