[en] High-resolution radio observations are presented of the flat-spectrum, 1-arcsec double radio source 1830-211. Optical CCD imaging in the I-band shows an ∼ 22-mag object coincident with the radio source position. We find that the unique nature of 1830-211 may be understood in terms of gravitational imaging of a background compact flat-spectrum radio source by a foreground galaxy. A lensing model is presented for the compact as well as the extended emission features, and possible tests to confirm the lens hypothesis are outlined. (author)

[en] Radio observations are presented of the source 1830-211 whose structure is anomalous in relation to its spectrum. The flat-spectrum source has well-defined double structure with components of nearly equal flux densities and separated by ∼ 1 arcsec. The source does not fit into any of the known classes. It is possible that the double structure is due to gravitational lensing of a single flat-spectrum source by the potential of a foreground galaxy, but even this does not fully explain all the observations. (author)

[en] The possibility that the diffuse X-ray background (XRB) could have been generated by the infall of baryons into the potential wells of dark matter is investigated within the framework of a hot dark matter (neutrino)-dominated universe. The XRB spectrum is fitted with the thermal bremsstrahlung kernel, and constraints on the nature of the infall and properties of the X-ray emitting gas are derived. The results indicate that around xi = 5 infall results in the formation of high-density knots with a hot plasma phase constituting 1 percent or less of the baryonic content of the universe. These dense regions can be regarded as the progenitors of present-day galaxies. Constraints are also derived for forms of dark matter other than neutrinos. 60 refs

[en] The Australia Telescope Low-brightness Survey (ATLBS) regions have been mosaic imaged at a radio frequency of 1.4 GHz with 6'' angular resolution and 72 μJy beam^–1 rms noise. The images (centered at R.A. 00^h35^m00^s, decl. –67°00'00'' and R.A. 00^h59^m17^s, decl. –67°00'00'', J2000 epoch) cover 8.42 deg² sky area and have no artifacts or imaging errors above the image thermal noise. Multi-resolution radio and optical r-band images (made using the 4 m CTIO Blanco telescope) were used to recognize multi-component sources and prepare a source list; the detection threshold was 0.38 mJy in a low-resolution radio image made with beam FWHM of 50''. Radio source counts in the flux density range 0.4-8.7 mJy are estimated, with corrections applied for noise bias, effective area correction, and resolution bias. The resolution bias is mitigated using low-resolution radio images, while effects of source confusion are removed by using high-resolution images for identifying blended sources. Below 1 mJy the ATLBS counts are systematically lower than the previous estimates. Showing no evidence for an upturn down to 0.4 mJy, they do not require any changes in the radio source population down to the limit of the survey. The work suggests that automated image analysis for counts may be dependent on the ability of the imaging to reproduce connecting emission with low surface brightness and on the ability of the algorithm to recognize sources, which may require that source finding algorithms effectively work with multi-resolution and multi-wavelength data. The work underscores the importance of using source lists—as opposed to component lists—and correcting for the noise bias in order to precisely estimate counts close to the image noise and determine the upturn at sub-mJy flux density.

[en] The first investigation of the axes of extragalactic extended radio sources in a 3CR sample indicated that there was a tendency for the axes to lie parallel to each other for sources separated by < or approx. 10⁰ on the sky. The authors have now attempted to verify the effect using two source samples, but find no significant tendency for axis alignment. They also investigated a sample formed by adding well-observed radio quasars to 3CR sources and found that the effect shows up only at a marginally significant level (< 2 σ). (author)

[en] Based on the Australia Telescope Low Brightness Survey (ATLBS) we present a sample of extended radio sources and derive morphological properties of faint radio sources. One hundred nineteen radio galaxies form the ATLBS Extended Source Sample (ATLBS-ESS) consisting of all sources exceeding 30'' in extent and integrated flux densities exceeding 1 mJy. We give structural details along with information on galaxy identifications and source classifications. The ATLBS-ESS, unlike samples with higher flux-density limits, has almost equal fractions of FR-I and FR-II radio galaxies, with a large fraction of the FR-I population exhibiting 3C31-type structures. Significant asymmetry in lobe extents appears to be a common occurrence in the ATLBS-ESS FR-I sources compared with FR-II sources. We present a sample of 22 FR-Is at z > 0.5 with good structural information. The detection of several giant radio sources, with size exceeding 0.7 Mpc, at z > 1 suggests that giant radio sources are not less common at high redshifts. The ESS also includes a sample of 28 restarted radio galaxies. The relative abundance of dying and restarting sources is indicative of a model where radio sources undergo episodic activity in which an active phase is followed by a brief dying phase that terminates with restarting of the central activity; in any massive elliptical a few such activity cycles wherein adjacent events blend may constitute the lifetime of a radio source and such bursts of blended activity cycles may be repeated over the age of the host. The ATLBS-ESS includes a 2 Mpc giant radio galaxy with the lowest surface brightness lobes known to date.

[en] We have detected the four 18 cm OH lines from the z∼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∼0.765 absorber and the z∼0.685 lens toward B0218+357 to place stringent constraints on changes in F≡g_p[α²/μ]^1.57. We obtain [ΔF/F]=(0.44±0.36^stat±1.0^syst)x10^-5, consistent with no evolution over the redshift range 0< z < or approx. 0.7. The measurements have a 2σ sensitivity of [Δα/α]<6.7x10^-6 or [Δμ/μ]<1.4x10^-5 to fractional changes in α and μ over a period of ∼6.5 G yr, half the age of the Universe. These are among the most sensitive constraints on changes in μ

[en] We present a Stokes I, Q and U survey at 189 MHz with the Murchison Widefield Array 32 element prototype covering 2400 deg². The survey has a 15.6 arcmin angular resolution and achieves a noise level of 15 mJy beam^–1. We demonstrate a novel interferometric data analysis that involves calibration of drift scan data, integration through the co-addition of warped snapshot images, and deconvolution of the point-spread function through forward modeling. We present a point source catalog down to a flux limit of 4 Jy. We detect polarization from only one of the sources, PMN J0351-2744, at a level of 1.8% ± 0.4%, whereas the remaining sources have a polarization fraction below 2%. Compared to a reported average value of 7% at 1.4 GHz, the polarization fraction of compact sources significantly decreases at low frequencies. We find a wealth of diffuse polarized emission across a large area of the survey with a maximum peak of ∼13 K, primarily with positive rotation measure values smaller than +10 rad m^–2. The small values observed indicate that the emission is likely to have a local origin (closer than a few hundred parsecs). There is a large sky area at α ≥ 2^h30^m where the diffuse polarized emission rms is fainter than 1 K. Within this area of low Galactic polarization we characterize the foreground properties in a cold sky patch at (α, δ) = (4^h, –27.°6) in terms of three-dimensional power spectra.