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.

The WiggleZ Dark Energy Survey: Joint measurements of the expansion and growth history at z < 1

Abstract: We perform a joint determination of the distance-redshift relation and cosmic expansion rate at redshifts z = 0.44, 0.6 and 0.73 by combining measurements of the baryon acoustic peak and Alcock-Paczynski distortion from galaxy clustering in the WiggleZ Dark Energy Survey, using a large ensemble of mock catalogues to calculate the covariance between the measurements. We find that D_A(z) = (1205 +/- 114, 1380 +/- 95, 1534 +/- 107) Mpc and H(z) = (82.6 +/- 7.8, 87.9 +/- 6.1, 97.3 +/- 7.0) km/s/Mpc at these three redshifts. Further combining our results with other baryon acoustic oscillation and distant supernovae datasets, we use a Monte Carlo Markov Chain technique to determine the evolution of the Hubble parameter H(z) as a stepwise function in 9 redshift bins of width dz = 0.1, also marginalizing over the spatial curvature. Our measurements of H(z), which have precision better than 7% in most redshift bins, are consistent with the expansion history predicted by a cosmological-constant dark-energy model, in which the expansion rate accelerates at redshift z < 0.7.

INTEGRATED POLARIZATION OF SOURCES AT λ ∼ 1 m AND NEW ROTATION MEASURE AMBIGUITIES

Abstract: We present an analysis of the polarization of compact radio sources from six pointings of the Westerbork Synthesis Radio Telescope at 350 MHz with 35% coverage in {lambda}{sup 2}. After correcting for the off-axis instrumental polarization with a simple analytical model, only a small number of 585 strong sources have significant polarizations at these wavelengths. The median depolarization ratio from 1.4 GHz for the strongest sources is <0.2, reinforcing the likelihood that radio galaxies are found in magnetized environments, even outside of rich clusters. Seven sources with significant 350 MHz polarization were selected for a more in-depth Faraday structure analysis. We fit the observed values Q/I and U/I as a function of {lambda}{sup 2} using both a depolarizing screen and two-component models. We also performed rotation measure (RM) Synthesis/Clean and standard fitting of polarization angle versus {lambda}{sup 2}. We find that a single RM, as found using polarization angle fitting or simple screen models, commonly provides a poor fit when the solutions are translated back into Q, U space. Thus, although a single 'characteristic' RM may be found using these techniques, the Faraday structure of the source may not be adequately represented. We also demonstrate that RM Synthesis may yieldmore » an erroneous Faraday structure in the presence of multiple, interfering RM components, even when cleaning of the Faraday spectrum is performed. We briefly explore the conditions under which RMs and Faraday structure results can be reliable. Many measurements in the literature do not meet these criteria; we discuss how these influence the resulting scientific conclusions and offer a prescription for obtaining reliable RMs.« less

Planck early results. XV. Spectral energy distributions and radio continuum spectra of northern extragalactic radio sources

Abstract: Spectral energy distributions (SEDs) and radio continuum spectra are presented for a northern sample of 104 extragalactic radio sources. based on the Planck Early Release Compact Source Catalogue (ERCSC) and simultaneous multi frequency data. The nine Planck frequencies, from 30 to 857 GHz, are complemented by a set of simultaneous observations ranging from radio to gamma-rays. This is the first extensive frequency coverage in the radio and millimetre domains for an essentially complete sample of extragalactic radio sources, and it shows how the individual shocks, each in their own phase of development, shape the radio spectra as they move in the relativistic jet. The SEDs presented in this paper were fitted with second and third degree polynomials to estimate the frequencies of the synchrotron and inverse Compton (IC) peaks, and the spectral indices of low and high frequency radio data, including the Planck ERCSC data, were calculated. SED modelling methods are discussed, with an emphasis on proper. physical modelling of the synchrotron bump using multiple components. Planck ERCSC data also suggest that the original accelerated electron energy spectrum could be much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The implications of this are discussed for the acceleration mechanisms effective in blazar shock. Furthermore in many cases the Planck data indicate that gamma-ray emission must originate in the same shocks that produce the radio emission.

The nature of the optical–radio correlations for powerful radio galaxies

Abstract: The nature of the optical–radio correlations for powerful radio galaxies is investigated using spectroscopic observations of a complete sample of southern 2-Jy radio sources. In line with previous work, we find that significant correlations exist between the luminosities of the [O III]λ 5007, [O II]λ 3727 and Hβ emission lines and the radio luminosity. However, our observations are not easily reconciled with the idea that these correlations are caused by the increase in the power of the photoionizing quasar as the jet power increases, with average ISM properties not changing appreciably with redshift or radio power: not only do we find that the scatter in the L[O iii] versus Lradio correlation is significantly larger than in L[O ii] versus Lradio and LHβ versus Lradio correlations, but the ionization state deduced from the emission lines does not increase with radio power as predicted by the simple, constant ISM, photoionization model. We conclude that (a) there exists a considerable range in the quasar ionizing luminosity at a given redshift, and (b) the mean density of the emission-line clouds is larger in the high-redshift/high-power radio sources. The latter density enhancement may be either a consequence of the increased importance of jet–cloud interactions or, alternatively, the result of a higher pressure in the confining hot ISM, in the high-redshift objects. Apart from the general scatter in the correlations, we identify a distinct group of objects with [O III]λ 5007 luminosities which are more than an order of magnitude lower than in the general population radio galaxies at similar redshift. These weak-line radio galaxies (WLRGs) are likely to be sources in which the central ionizing quasars are particularly feeble. Deep spectra show that many of the sources in our sample are broad-line radio galaxies (BLRGs). The fact that the BLRGs are observed out to the redshift limit of the survey, overlapping in redshift with the quasars, argues against the idea that BLRGs are simply the low-radio-power counterparts of high-power, high-redshift quasars. Either there exists a considerable range in the intrinsic luminosities of the broad-line AGN for a given redshift or radio power, or the BLRGs represent partially obscured quasars. The degree of scatter present in the L[Oiii] versus Lradio correlation supports the former possibility.

Constraints on changes in fundamental constants from a cosmologically distant OH absorber or emitter

Abstract: We have detected the four 18 cm OH lines from the $z\ensuremath{\sim}0.765$ gravitational lens toward PMN J0134--0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the $z\ensuremath{\sim}0.765$ absorber and the $z\ensuremath{\sim}0.685$ lens toward $\mathrm{B}0218+357$ to place stringent constraints on changes in $F\ensuremath{\equiv}{g}_{p}[{\ensuremath{\alpha}}^{2}/\ensuremath{\mu}{]}^{1.57}$. We obtain $[\ensuremath{\Delta}F/F]=(0.44\ifmmode\pm\else\textpm\fi{}{0.36}^{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1.0}^{\mathrm{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, consistent with no evolution over the redshift range $0lz\ensuremath{\lesssim}0.7$. The measurements have a $2\ensuremath{\sigma}$ sensitivity of $[\ensuremath{\Delta}\ensuremath{\alpha}/\ensuremath{\alpha}]l6.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ or $[\ensuremath{\Delta}\ensuremath{\mu}/\ensuremath{\mu}]l1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ to fractional changes in $\ensuremath{\alpha}$ and $\ensuremath{\mu}$ over a period of $\ensuremath{\sim}6.5\text{ }\text{ }\mathrm{G}\text{ }\mathrm{yr}$, half the age of the Universe. These are among the most sensitive constraints on changes in $\ensuremath{\mu}$.