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We present the S-Band Polarization All Sky Survey (S-PASS), a survey of polarized radio emission over the southern sky at Dec. <−1° taken with the Parkes radio telescope at 2.3 GHz. The main aim was to observe at a frequency high enough to avoid strong depolarization at intermediate Galactic latitudes (still present at 1.4 GHz) to study Galactic magnetism, but low enough to retain ample signal-to-noise ratio (S/N) at high latitudes for extragalactic and cosmological science. We developed a new scanning strategy based on long azimuth scans and a corresponding map-making procedure to make recovery of the overall mean signal of Stokes Q and U possible, a long-standing problem with polarization observations. We describe the scanning strategy, map-making procedure and validation tests. The overall mean signal is recovered with a precision better than 0.5 per cent. The maps have a mean sensitivity of 0.81 mK on beam-size scales and show clear polarized signals, typically to within a few degrees of the Galactic plane, with ample S/N everywhere (the typical signal in low-emission regions is 13 mK and 98.6 per cent of pixels have S/N > 3). The largest depolarization areas are in the inner Galaxy, associated with the Sagittarius Arm. We have also computed a rotation measure map combining S-PASS with archival data from the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck experiments. A Stokes I map has been generated, with sensitivity limited to the confusion level of 9 mK. [ABSTRACT FROM AUTHOR]

We identify a counterpart to a Galactic supershell in diffuse radio polarization, and use this to determine the magnetic fields associated with this object. GSH 006 − 15 + 7 has perturbed the polarized emission at 2.3 GHz, as observed in the S-band Polarization All Sky Survey (S-PASS), acting as a Faraday screen. We model the Faraday rotation over the shell, and produce a map of Faraday depth over the area across it. Such models require information about the polarized emission behind the screen, which we obtain from the Wilkinson Microwave Anisotropy Probe (WMAP), scaled from 23 to 2.3 GHz, to estimate the synchrotron background behind GSH 006 − 15 + 7. Using the modelled Faraday thickness, we determine the magnitude and the plane-of-the-sky structure of the line-of-sight magnetic field in the shell. We find a peak line-of-sight field strength of $$|B_\parallel |_\text{peak}=2.0^{+0.01 }_{ -0.7}\, \mu$$ G. Our measurement probes weak magnetic fields in a low-density regime (number densities of $${\sim }0.4\,$$ cm−3) of the ISM, thus providing crucial information about the magnetic fields in the partially-ionized phase. [ABSTRACT FROM AUTHOR]

We report the detection of a new Galactic bubble at the interface between the halo and the Galactic disc. We suggest that the nearby Lupus complex and parts of the Ophiuchus complex constitute the denser parts of the structure. This young bubble, ≲3 Myr old, could be the remnant of a supernova and it expands inside a larger HI loop that has been created by the outflows of the Upper Scorpius OB association. An HI cavity filled with hot X-ray gas is associated with the structure, which is consistent with the Galactic chimney scenario. The X-ray emission extends beyond the west and north-west edges of the bubble, suggesting that hot gas outflows are breaching the cavity, possibly through the fragmented Lupus complex. Analyses of the polarised radio synchrotron and of the polarised dust emission of the region suggest the connection of the Galactic centre spur with the young Galactic bubble. A distribution of HI clumps that spatially corresponds well to the cavity boundaries was found at VLSR ≃−100 km s−1. Some of these HI clumps are forming jets, which may arise from the fragmented part of the bubble. We suggest that these clumps might be "dripping" cold clouds from the shell walls inside the cavity that is filled with hot ionised gas. It is possible that some of these clumps are magnetised and were then accelerated by the compressed magnetic field at the edge of the cavity. Such a mechanism would challenge the Galactic accretion and fountain model, where high-velocity clouds are considered to be formed at high Galactic latitude from hot gas flows from the Galactic plane. [ABSTRACT FROM AUTHOR]

We compare two rotationally invariant decomposition techniques on linear polarization data: the spin-2 spherical harmonic decomposition in two opposite parities, the E- and B-mode, and the multiscale analysis of the gradient of linear polarization, ∣∇ P∣. We demonstrate that both decompositions have similar properties in the image domain and the spatial frequency domain. They can be used as complementary tools for turbulence analysis of interstellar magnetic fields in order to develop a better understanding of the origin of energy sources for the turbulence, the origin of peculiar magnetic field structures and their underlying physics. We also introduce a new quantity ∣∇EB∣ based on the E- and B-modes and we show that in the intermediate- and small-scale limit ∣∇EB∣ ≅ ∣∇P∣. Analysis of the 2.3 GHz S-band Polarization All Sky Survey shows many extended coherent filament-like features appearing as 'double jumps' in the ∣∇ P∣ map that are correlated with negative and positive filaments of B-type polarization. These local asymmetries between the two polarization types, E and B, of the non-thermal Galactic synchrotron emission have an influence on the E- and B-mode power spectra analyses. The wavelet-based formalism of the polarization gradient analysis allows us to locate the position of E- or B-mode features responsible for the local asymmetries between the two polarization types. In analysed subregions, the perturbations of the magnetic field are trigged by star clusters associated with HII regions, the Orion-Eridanus superbubble and the North Polar Spur at low Galactic latitude. [ABSTRACT FROM AUTHOR]

Aims. Radio synchrotron polarization maps of the Galaxy can be used to infer the properties of interstellar turbulence in the diffuse magneto-ionic medium (MIM). In this paper, we investigate the normalized spatial gradient of linearly polarized synchrotron emission (∣∇P∣/∣P∣) as a tracer of turbulence, the relationship of the gradient to the sonic Mach number of the MIM, and changes in morphology of the gradient as a function of Galactic position in the southern sky. Methods. We used data from the S-band Polarization All Sky Survey (S-PASS) to image the normalized spatial gradient of the linearly polarized synchrotron emission (∣∇P∣/∣P∣) in the entire southern sky at 2.3 GHz. The spatial gradient of linear polarization reveals rapid changes in the density and magnetic fluctuations in the MIM due to magnetic turbulence as a function of Galactic position. We made comparisons of these data to ideal MHD numerical simulations. To constrain the sonic Mach number (Ms), we applied a high-order moments analysis to the observations and to the simulated diffuse, isothermal ISM with ideal magneto-hydrodynamic turbulence. Results. We find that polarization gradient maps reveal elongated structures, which we associate with turbulence in the MIM. Our analysis indicates that turbulent MIM is in a generally transonic regime. This result for the turbulent regime is more general than the ones deduced by the analysis of electron density variation data, because it is based on the stochastic imprints of the Faraday rotation effect, which is also sensitive to the magnetic field fluctuations. Filamentary structures are seen with typical widths down to the angular resolution, and the observed morphologies closely match numerical simulations and, in some cases, Hα contours. The ∣∇P∣/∣P∣ intensity is found to be approximately log-normal distributed. No systematic variations in the sonic Mach number are observed as a function of Galactic coordinates, which is consistent with turbulence in the WIM, as inferred by the analysis of Hα data. We conclude that the sonic Mach number of the diffuse MIM appears to be spatially uniform towards the Galactic plane and the Sagittarius-Carina arm, but local variations induced by nearby extended objects are also found. [ABSTRACT FROM AUTHOR]

We have detected a radio bridge of unpolarized synchrotron emission connecting the NW relic of the galaxy cluster Abell 3667 to its central regions. We used data at 2.3 GHz from the S-band Polarization All Sky Survey and at 3.3 GHz from a follow-up observation, both conducted with the Parkes radio telescope. This emission is further aligned with a diffuse X-ray tail, and represents the most compelling evidence for an association between intracluster medium turbulence and diffuse synchrotron emission. This is the first clear detection of a bridge associated both with an outlying cluster relic and X-ray diffuse emission. All the indicators point towards the synchrotron bridge being related to the post-shock turbulent wake trailing the shock front generated by a major merger in a massive cluster. Although predicted by simulations, this is the first time such emission is detected with high significance and clearly associated with the path of a confirmed shock. Although the origin of the relativistic electrons is still unknown, the turbulent re-acceleration model provides a natural explanation for the large-scale emission. The equipartition magnetic field intensity of the bridge is Beq = 2.2 ± 0.3 μG. We further detect diffuse emission coincident with the central regions of the cluster for the first time. [ABSTRACT FROM PUBLISHER]

The H i Parkes All Sky Survey (HIPASS) is a blind extragalactic H i 21-cm emission-line survey covering the whole southern sky from declination −90° to +25°. The HIPASS catalogue (HICAT), containing 4315 H i-selected galaxies from the region south of declination +2°, is presented in Meyer et al. (Paper I). This paper describes in detail the completeness and reliability of HICAT, which are calculated from the recovery rate of synthetic sources and follow-up observations, respectively. HICAT is found to be 99 per cent complete at a peak flux of 84 mJy and an integrated flux of 9.4 Jy km s−1. The overall reliability is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy or integrated flux >8.2 Jy km s−1. Expressions are derived for the uncertainties on the most important HICAT parameters: peak flux, integrated flux, velocity width and recessional velocity. The errors on HICAT parameters are dominated by the noise in the HIPASS data, rather than by the parametrization procedure. [ABSTRACT FROM AUTHOR]

We present a Parkes multibeam H I survey of the Large Magellanic Cloud (LMC). This survey, which is sensitive to spatial structure in the range 200 pc to 10 kpc, complements the Australia Telescope Compact survey, which is sensitive to structure in the range 15-500 pc. With an rms column density sensitivity of 8 × 10[sup 16] cm[sup -2] for narrow lines and 4 × 10[sup 17] cm[sup -2] for typical linewidths of 40 km s[sup -1], emission is found to be extensive well beyond the main body of the LMC. Arm-like features extend from the LMC to join the Magellanic Bridge and the Leading Arm, a forward counterpart to the Magellanic Stream. These features, whilst not as dramatic as those in the Small Magellanic Cloud, appear to have a common origin in the Galactic tidal field, in agreement with recent 2MASS and DENIS results for the stellar population. The diffuse gas that surrounds the LMC, particularly at PAs of 90°-330°, appears to be loosely associated with tidal features, but loosening by the ram pressure of tenuous Galactic halo gas against the outer parts of the LMC cannot be discounted. High-velocity clouds, which lie between the Galaxy and the LMC in velocity and that appear in the ultraviolet spectra of some LMC stars, are found to be associated with the LMC if their heliocentric velocity exceeds approximately + 100 km s[sup -1]. They are possibly the product of energetic outflows from the LMC disc. The H I mass of the LMC is found to be (4.8 ± 0.2) × 10[sup 8] M[sub ⊙] (for an assumed distance of 50 kpc), substantially more than previous recent measurements. [ABSTRACT FROM AUTHOR]