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Magnetic fields in the ionized medium of the disk and halo of the Milky Way impose Faraday rotation on linearly polarized radio emission. We compare two surveys mapping the Galactic Faraday rotation, one showing the rotation measures of extragalactic sources seen through the Galaxy (from Hutschenreuter et al 2022), and one showing the Faraday depth of the diffuse Galactic synchrotron emission from the Global Magneto-Ionic Medium Survey. Comparing the two data sets in 5deg x 10deg bins shows good agreement at intermediate latitudes, 10 < |b| < 50 deg, and little correlation between them at lower and higher latitudes. Where they agree, both tracers show clear patterns as a function of Galactic longitude: in the Northern Hemisphere a strong sin(2 x longitude) pattern, and in the Southern hemisphere a sin(longitude + pi) pattern. Pulsars with height above or below the plane |z| > 300 pc show similar longitude dependence in their rotation measures. Nearby non-thermal structures show rotation measure shadows as does the Orion-Eridanus superbubble. We describe families of dynamo models that could explain the observed patterns in the two hemispheres. We suggest that a field reversal, known to cross the plane a few hundred pc inside the solar circle, could shift to positive z with increasing Galactic radius to explain the sin(2xlongitude) pattern in the Northern Hemisphere. Correlation shows that rotation measures from extragalactic sources are one to two times the corresponding rotation measure of the diffuse emission, implying Faraday complexity along some lines of sight, especially in the Southern hemisphere., 37 pages, 26 figures, Ap. J. accepted

Using the Global Magneto-Ionic Medium Survey (GMIMS) Low-Band South (LBS) southern sky polarization survey, covering 300 to 480 MHz at 81 arcmin resolution, we reveal the brightest region in the Southern polarized sky at these frequencies. The region, G150-50, covers nearly 20deg$^2$, near (l,b)~(150 deg,-50 deg). Using GMIMS-LBS and complementary data at higher frequencies (~0.6--30 GHz), we apply Faraday tomography and Stokes QU-fitting techniques. We find that the magnetic field associated with G150-50 is both coherent and primarily in the plane of the sky, and indications that the region is associated with Radio Loop II. The Faraday depth spectra across G150-50 are broad and contain a large-scale spatial gradient. We model the magnetic field in the region as an expanding shell, and we can reproduce both the observed Faraday rotation and the synchrotron emission in the GMIMS-LBS band. Using QU-fitting, we find that the Faraday spectra are produced by several Faraday dispersive sources along the line-of-sight. Alternatively, polarization horizon effects that we cannot model are adding complexity to the high-frequency polarized spectra. The magnetic field structure of Loop II dominates a large fraction of the sky, and studies of the large-scale polarized sky will need to account for this object. Studies of G150-50 with high angular resolution could mitigate polarization horizon effects, and clarify the nature of G150-50., 25 pages, 14 figures. Accepted for publication in MNRAS

Using the Australian Square Kilometre Array Pathfinder to measure 21-cm absorption spectra toward continuum background sources, we study the cool phase of the neutral atomic gas in the far outer disk, and in the inner Galaxy near the end of the Galactic bar at longitude 340 degrees. In the inner Galaxy the cool atomic gas has a smaller scale height than in the solar neighborhood, similar to the molecular gas and the superthin stellar population in the bar. In the outer Galaxy the cool atomic gas is mixed with the warm, neutral medium, with the cool fraction staying roughly constant with Galactic radius. The mean spin temperature, i.e. the ratio of the emission brightness temperature to the absorption, is roughly constant for velocities corresponding to Galactic radius greater than about twice the solar circle radius. The ratio has a value of about 300 K, but this does not correspond to a physical temperature in the gas. If the gas causing the absorption has kinetic temperature of about 100 K, as in the solar neighborhood, then the value 300 K indicates that the fraction of the gas mass in this phase is one-third of the total HI mass., Comment: 29 pages, 12 figures, submitted to Astrophysical Journal

We present the first unbiased survey of neutral hydrogen (HI) absorption in the Small Magellanic Cloud (SMC). The survey utilises pilot HI observations with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope as part of the Galactic ASKAP HI (GASKAP-HI) project whose dataset has been processed with the GASKAP-HI absorption pipeline, also described here. This dataset provides absorption spectra towards 229 continuum sources, a 275% increase in the number of continuum sources previously published in the SMC region, as well as an improvement in the quality of absorption spectra over previous surveys of the SMC. Our unbiased view, combined with the closely matched beam size between emission and absorption, reveals a lower cold gas faction (11%) than the 2019 ATCA survey of the SMC and is more representative of the SMC as a whole. We also find that the optical depth varies greatly between the SMC's bar and wing regions. In the bar we find that the optical depth is generally low (correction factor to the optically thin column density assumption of $\mathcal{R}_{\rm HI} \sim 1.04$) but increases linearly with column density. In the wing however, there is a wide scatter in optical depth despite a tighter range of column densities., Comment: Accepted for publication in PASA, 19 pages, 17 figures, 5 tables

Observations of synchrotron emission at low radio frequencies reveal a labyrinth of polarised Galactic structures. However, the explanation for the wealth of structures remains uncertain due to the complex interactions between the interstellar medium and the magnetic field. A multi-tracer approach to the analysis of large sky areas is needed. This paper aims to use polarimetric images from the LOFAR Two metre Sky Survey (LoTSS) to produce the biggest mosaic of polarised emission in the northern sky at low radio frequencies (150 MHz) to date. The large area this mosaic covers allows for detailed morphological and statistical studies of polarised structures in the high-latitude outer Galaxy, including the well-known Loop III region. We produced a 3100 square degree Faraday tomographic cube using a rotation measure synthesis tool. We calculated the statistical moments of Faraday spectra and compared them with data sets at higher frequencies (1.4 GHz) and with a map of a rotation measure derived from extragalactic sources. The mosaic is dominated by polarised emission connected to Loop III. Additionally, the mosaic reveals an abundance of other morphological structures, mainly {narrow and extended} depolarisation canals, which are found to be ubiquitous. We find a correlation between the map of an extragalactic rotation measure and the LoTSS first Faraday moment image. The ratio of the two deviates from a simple model of a Burn slab (Burn 1966) along the line of sight, which highlights the high level of complexity in the magnetoionic medium that can be studied at these frequencies., 20 pages, 25 figures, accepted for publication in A&A

The Southern HII Region Discovery Survey (SHRDS) is a 900 hour Australia Telescope Compact Array 4-10 GHz radio continuum and radio recombination line (RRL) survey of Galactic HII regions and infrared-identified HII region candidates in the southern sky. For this data release, we reprocess all previously published SHRDS data and include an additional ~450 hours of observations. The search for new HII regions is now complete over the range 259 deg < Galactic longitude < 346 deg, |Galactic latitude| < 4 deg for HII region candidates with predicted 6 GHz continuum peak brightnesses >30 mJy/beam. We detect radio continuum emission toward 730 targets altogether including previously known nebulae and HII region candidates. By averaging ~18 RRL transitions, we detect RRL emission toward 206 previously known HII regions and 436 HII region candidates. Including the northern sky surveys, over the last decade the HII Region Discovery Surveys have more than doubled the number of known Galactic HII regions. The census of HII regions in the WISE Catalog of Galactic HII Regions is now complete for nebulae with 9 GHz continuum flux densities > 250 mJy. We compare the RRL properties of the newly discovered SHRDS nebulae with those of all previously known HII regions. The median RRL full-width at half-maximum line width of the entire WISE Catalog HII region population is 23.9 km/s and is consistent between Galactic quadrants. The observed Galactic longitude-velocity asymmetry in the population of HII regions probably reflects underlying spiral structure in the Milky Way., 37 pages, 10 figures, 11 tables (full tables in machine readable format available in the online journal), 1 appendix. Survey website: https://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/community/shrds/

Symbiotic stars show emission across the electromagnetic spectrum from a wide array of physical processes. At cm-waves both synchrotron and thermal emission is seen, often highly variable and associated with outbursts in the optical and X-rays. Most models of the radio emission include an ionized region within the dense wind of the red giant star, that is kept ionized by activity on the white dwarf companion or its accretion disk. In some cases there is on-going shell burning on the white dwarf due to its high mass accretion rate or a prior nova eruption, in other cases nuclear fusion occurs only occasionally as recurrent nova events. In this study we measure the spectral indices of a sample of symbiotic systems in the Southern Hemisphere using the Australia Telescope Compact Array. Putting our data together with results from other surveys, we derive the optical depths and brightness temperatures of some well-known symbiotic stars. Using parallax distances from Gaia Data Release 3, we determine the sizes and characteristic electron densities in the radio emission regions. The results show a range of a factor of 10^4 in radio luminosity, and a factor of 100 in linear size. These numbers are consistent with a picture where the rate of shell burning on the white dwarf determines the radio luminosity. Therefore, our findings also suggest that radio luminosity can be used to determine whether a symbiotic star is powered by accretion alone or also by shell burning., Ap.J. accepted for publication

Tracing the transition between the diffuse atomic interstellar medium (ISM) and cold, dense gas is crucial for deciphering the star formation cycle in galaxies. Here we present MACH, a new survey of cold neutral hydrogen (HI) absorption at $21\rm\,cm$ by the Karl G. Jansky Very Large Array. We target 42 bright background sources with $600.001$ are ubiquitous ($c\sim100\%$), whereas high optical depths ($\tau>1$) are extremely rare ($c\sim0\%$)., Comment: 33 pages, 16 figures. Accepted for publication in ApJS

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Atomic ionised regions with strong continuum emission are often associated with regions of high-mass star formation and low-frequency (, Comment: 18 pages, 19 Figures, Accepted by MNRAS

We have studied the small scale distribution of atomic hydrogen (HI) using 21-cm absorption spectra against multiple-component background radio continuum sources from the 21-SPONGE survey and the Millennium Arecibo Absorption Line Survey. We have found $>5\sigma$ optical depth variations at a level of $\sim0.03-0.5$ between 13 out of 14 adjacent sightlines separated by a few arcseconds to a few arcminutes, suggesting the presence of neutral structures on spatial scales from a few to thousands of AU (which we refer to as tiny scale atomic structure, TSAS). The optical depth variations are strongest in directions where the HI column density and the fraction of HI in the cold neutral medium (CNM) are highest, which tend to be at low Galactic latitudes. By measuring changes in the properties of Gaussian components fitted to the absorption spectra, we find that changes in both the peak optical depth and the linewidth of TSAS absorption features contribute to the observed optical depth variations, while changes in the central velocity do not appear to strongly impact the observed variations. Both thermal and turbulent motions contribute appreciably to the linewidths, but the turbulence does not appear strong enough to confine overpressured TSAS. In a majority of cases, the TSAS column densities are sufficiently high that these structures can radiatively cool fast enough to maintain thermal equilibrium with their surroundings, even if they are overpressured. We also find that a majority of TSAS is associated with the CNM. For TSAS in the direction of the Taurus molecular cloud and the local Leo cold cloud, we estimate densities over an order of magnitude higher than typical CNM densities., Comment: 29 pages, 19 figures, 4 tables. Accepted to ApJ. Section 4.3.1 updated from previous version

We present a case study whereby ecological research on fallen trees in forest plots was advanced by a collaboration with astronomers working on the vector fields of stars and gas, and we propose a framework by which such novel collaborations can progress.

The spatial analysis of dimensionless points (e.g., tree locations on a plot map) is common in ecology, for instance using point-process statistics to detect and compare patterns. However, the treatment of one-dimensional linear features (fiber processes) is rarely attempted. Here we appropriate the methods of vector sums and dot products, used regularly in fields like astrophysics, to analyze a data set of mapped linear features (logs) measured in 12 × 1-ha forest plots. For this demonstrative case study, we ask two deceptively simple questions: do trees tend to fall downhill, and if so, does slope gradient matter? Despite noisy data and many potential confounders, we show clearly that topography (slope direction and steepness) of forest plots does matter to treefall. More generally, these results underscore the value of mathematical methods of physics to problems in the spatial analysis of linear features, and the opportunities that interdisciplinary collaboration provides. This work provides scope for a variety of future ecological analyzes of fiber processes in space.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is by far the largest telescope of any kind ever built. FAST produced its first light in September 2016 and it is now under commissioning, with normal operation to commence in late 2019. During testing and early science operation, FAST has started making astronomical discoveries, particularly pulsars of various kinds, including millisecond pulsars, binaries, gamma-ray pulsars, etc. The papers in this mini-volume propose ambitious observational projects to advance our knowledge of astronomy, astrophysics and fundamental physics in many ways. Although it may take FAST many years to achieve all the goals explained in these papers, taken together they define a powerful strategic vision for the next decade., 2 pages, A preface to the RAA mini-volume on FAST science potential, topics including fundamental constants, cosmic rays, exoplanets, gravitational radiation, the interstellar medium, and masers

We present the first results from the Small Magellanic Cloud portion of a new Australia Telescope Compact Array (ATCA) HI absorption survey of both of the Magellanic Clouds, comprising over 800 hours of observations. Our new HI absorption line data allow us to measure the temperature and fraction of cold neutral gas in a low metallicity environment. We observed 22 separate fields, targeting a total of 55 continuum sources against 37 of which we detected HI absorption; from this we measure a column density weighted mean average spin temperature of $=150$ K. Splitting the spectra into individual absorption line features, we estimate the temperatures of different gas components and find an average cold gas temperature of $\sim{30}$ K for this sample, lower than the average of $\sim{40}$ K in the Milky Way. The HI appears to be evenly distributed throughout the SMC and we detect absorption in $67\%$ of the lines of sight in our sample, including some outside the main body of the galaxy ($N_{\text{HI}}>2\times{10^{21}}$ cm$^{-2}$). The optical depth and temperature of the cold neutral atomic gas shows no strong trend with location spatially or in velocity. Despite the low metallicity environment, we find an average cold gas fraction of $\sim{20\%}$, not dissimilar from that of the Milky Way., Comment: 22 pages, 16 figures, accepted for publication in ApJS

Carbon-bearing molecules, particularly CO, have been widely used as tracers of molecular gas in the interstellar medium (ISM). In this work, we aim to study the properties of molecules in diffuse, cold environments, where CO tends to be under-abundant and/or sub-thermally excited. We performed one of the most sensitive (down to $\mathrm{��_{rms}^{CO} \sim 0.002}$ and $\mathrm{��_{rms}^{HCO^+} \sim 0.0008}$) sub-millimeter molecular absorption line observations towards 13 continuum sources with the ALMA. CO absorption was detected in diffuse ISM down to $\mathrm{A_v< 0.32\,mag}$ and \hcop was down to $\mathrm{A_v < 0.2\,mag}$, where atomic gas and dark molecular gas (DMG) starts to dominate. Multiple transitions measured in absorption toward 3C454.3 allow for a direct determination of excitation temperatures $\mathrm{T_{ex}}$ of 4.1\,K and 2.7\,K, for CO and for \hcop, respectively, which are close to the cosmic microwave background (CMB) and provide explanation for their being undercounted in emission surveys. A stronger linear correlation was found between $\mathrm{N_{HCO^+}}$ and $\mathrm{N_{H_2}}$ (Pearson correlation coefficient P $\sim$ 0.93) than that of $\mathrm{N_{CO}}$ and $\mathrm{N_{H_2}}$ (P $\sim$ 0.33), suggesting \hcop\ being a better tracer of H$_2$ than CO in diffuse gas. The derived CO-to-\h2 conversion factor (the CO X-factor) of (14 $\pm$ 3) $\times$ 10$^{20}$ cm$^{-2}$ (K \kms)$^{-1}$ is approximately 6 times larger than the average value found in the Milky Way.

Faraday rotation occurs along every line of sight in the Galaxy; Rotation Measure (RM) synthesis allows a three-dimensional representation of the interstellar magnetic field. This study uses data from the Global Magneto-Ionic Medium Survey, a combination of single-antenna spectro-polarimetric studies, including northern sky data from the DRAO 26-m Telescope (1270-1750 MHz) and southern sky data from the Parkes 64-m Telescope (300-480 MHz). From the synthesized Faraday spectral cubes we compute the zeroth, first, and second moments to find the total polarized emission, mean and RM-width of the polarized emission. From DRAO first moments we find a weak vertical field directed from Galactic North to South, but Parkes data reveal fields directed towards the Sun at high latitudes in both hemispheres: the two surveys clearly sample different volumes. DRAO second moments show feature widths in Faraday spectra increasing with decreasing positive latitudes, implying that longer lines of sight encounter more Faraday rotating medium, but this is not seen at negative latitudes. Parkes data show the opposite: at positive latitudes the second moment decreases with decreasing latitude, but not at negative latitudes. Comparing first moments with RMs of pulsars and extragalactic sources and a study of depolarization together confirm that the DRAO survey samples to larger distances than the Parkes data. Emission regions in the DRAO survey are typically 700 to 1000 pc away, slightly beyond the scale-height of the magneto-ionic medium; emission detected in the Parkes survey is entirely within the magneto-ionic disk, less than 500 pc away., Astrophysical Journal in press

We report the first evidence of molecular gas in two atomic hydrogen (HI) clouds associated with gas outflowing from the Small Magellanic Cloud (SMC). We used the Atacama Pathfinder Experiment (APEX) to detect and spatially resolve individual clumps of CO(2-1) emission in both clouds. CO clumps are compact (~ 10 pc) and dynamically cold (linewidths < 1 km/s). Most CO emission appears to be offset from the peaks of the HI emission, some molecular gas lies in regions without a clear HI counterpart. We estimate a total molecular gas mass of 10^3-10^4 Msun in each cloud and molecular gas fractions up to 30% of the total cold gas mass (molecular + neutral). Under the assumption that this gas is escaping the galaxy, we calculated a cold gas outflow rate of 0.3-1.8 Msun/yr and mass loading factors of 3 -12 at a distance larger than 1 kpc. These results show that relatively weak star-formation-driven winds in dwarf galaxies like the SMC are able to accelerate significant amounts of cold and dense matter and inject it into the surrounding environment., Accepted for publication in ApJ Letters

Sharpless 2-27 (Sh2-27) is a nearby ${\rm H\,{\small II}}$ region excited by $\zeta$Oph. We present observations of polarized radio emission from 300 to 480$\,$MHz towards Sh2-27, made with the Parkes 64$\,$m Radio Telescope as part of the Global Magneto-Ionic Medium Survey. These observations have an angular resolution of $1.35^{\circ}$, and the data are uniquely sensitive to magneto-ionic structure on large angular scales. We demonstrate that background polarized emission towards Sh2-27 is totally depolarized in our observations, allowing us to investigate the foreground. We analyse the results of Faraday tomography, mapping the magnetised interstellar medium along the 165$\,$pc path to Sh2-27. The Faraday dispersion function in this direction has peaks at three Faraday depths. We consider both Faraday thick and thin models for this observation, finding that the thin model is preferred. We further model this as Faraday rotation of diffuse synchrotron emission in the Local Bubble and in two foreground neutral clouds. The Local Bubble extends for 80$\,$pc in this direction, and we find a Faraday depth of $-0.8 \pm 0.4\,$rad$\,$m$^{-2}$. This indicates a field directed away from the Sun with a strength of $-2.5\pm1.2\,\mu$G. The near and far neutral clouds are each about 30$\,$pc thick, and we find Faraday depths of $-6.6\pm0.6\,$rad$\,$m$^{-2}$ and $+13.7\pm0.8\,$rad$\,$m$^{-2}$, respectively. We estimate that the line-of-sight magnetic strengths in the near and far cloud are $B_{\parallel, \text{near}} \approx -15\,\mu\text{G}$ and $B_{\parallel, \text{far}} \approx +30\,\mu\text{G}$. Our results demonstrate that Faraday tomography can be used to investigate the magneto-ionic properties of foreground features in front of nearby ${\rm H\,{\small II}}$ regions., Comment: 14+4 pages, 10+6 figures, 2 tables. In press with MNRAS

Much data on the Galactic polarized radio emission has been gathered in the last five decades. All-sky surveys have been made, but only in narrow, widely spaced frequency bands, and the data are inadequate for the characterization of Faraday rotation, the main determinant of the appearance of the polarized radio sky at decimetre wavelengths. We describe a survey of the polarized radio emission from the Southern sky, aiming to characterize the magneto-ionic medium, particularly the strength and configuration of the magnetic field. This work is part of the Global Magneto-Ionic Medium Survey (GMIMS). We have designed and built a feed and receiver covering the band 300 to 900 MHz for the CSIRO Parkes 64-m Telescope. We have surveyed the entire sky between declinations -90 and +20 degrees. We present data covering 300 to 480 MHz with angular resolution 81' to 45'. The survey intensity scale is absolutely calibrated, based on measurements of resistors at known temperatures and on an assumed flux density and spectral index for Taurus A. Data are presented as brightness temperatures. We have applied Rotation Measure Synthesis to the data to obtain a Faraday depth cube of resolution 5.9 radians per metre squared, sensitivity of 60 mK of polarized intensity, and angular resolution 1.35 degrees. The data presented in this paper are available at the Canadian Astronomy Data Centre., Accepted for publication in the Astronomical Journal Modified 29th June 2019 to replace outdated doi: for access to data

The Galactic interstellar medium hosts a significant magnetic field, which can be probed through the synchrotron emission produced from its interaction with relativistic electrons. Linearly polarized synchrotron emission is generated throughout the Galaxy, and at longer wavelengths, modified along nearly every path by Faraday rotation in the intervening magneto-ionic medium. Full characterization of the polarized emission requires wideband observations with many frequency channels. We have surveyed polarized radio emission from the Northern sky over the the range 1280-1750 MHz, with channel width 236.8 kHz, using the John A. Galt Telescope (diameter 25.6 m) at the Dominion Radio Astrophysical Observatory, as part of the Global Magneto-Ionic Medium Survey. The survey covered 72% of the sky, declinations -30 to +87 degrees at all right ascensions. The intensity scale was absolutely calibrated, based on the flux density and spectral index of Cygnus A. Polarization angle was calibrated using the extended polarized emission of the Fan Region. Data are presented as brightness temperatures with angular resolution 40'. Sensitivity in Stokes Q and U is 45 mK rms in a 1.18 MHz band. We have applied rotation measure synthesis to the data to obtain a Faraday depth cube of resolution 150 radians per square metre and sensitivity 3 mK rms of polarized intensity. Features in Faraday depth up to a width of 110 radians per square metre are represented. The maximum detectable Faraday depth is +/- 20,000 radians per square metre. The survey data are available at the Canadian Astronomy Data Centre., Comment: Accepted for publication in the Astronomical Journal

Optical depth variations in the Galactic neutral interstellar medium (ISM) with spatial scales from hundreds to thousands of astronomical units have been observed through HI absorption against pulsars and continuum sources, while extremely small structures with spatial scales of tens of astronomical units remain largely unexplored. The nature and formation of such tiny-scale atomic structures (TSAS) need to be better understood. We report a tentative detection of TSAS with a signal-to-noise ratio of 3.2 toward PSR B1557$-$50 in the second epoch of two Parkes sessions just 0.36 yr apart, which are the closest-spaced spectral observations toward this pulsar. One absorption component showing marginal variations has been identified. Based on the pulsar's proper motion of 14 mas $\rm yr^{-1}$ and the component's kinematic distance of 3.3 kpc, the corresponding characteristic spatial scale is 17 au, which is among the smallest sizes of known TSAS. Assuming a similar line-of-sight (LOS) depth, the tentative TSAS cloud detected here is overdense and overpressured relative to the cold neutral medium (CNM), and can radiatively cool fast enough to be in thermal equilibrium with the ambient environment. We find that turbulence is not sufficient to confine the overpressured TSAS. We explore the LOS elongation that would be required for the tentative TSAS to be at the canonical CNM pressure, and find that it is $\sim5000$ -- much larger than filaments observed in the ISM. We see some evidence of line width and temperature variations in the CNM components observed at the two epochs, as predicted by models of TSAS-like cloud formation colliding warm neutral medium flows., Comment: 11 pages, 2 figures, 2 tables, accepted for publication in the ApJL

The census of Galactic HII regions is vastly incomplete in the Southern sky. We use the Australia Telescope Compact Array (ATCA) to observe 4-10 GHz radio continuum and hydrogen radio recombination line (RRL) emission from candidate HII regions in the Galactic zone 259 deg < l < 344 deg, |b| < 4 deg. In this first data release, we target the brightest HII region candidates and observe 282 fields in the direction of at least one previously-known or candidate HII region. We detect radio continuum emission and RRL emission in 275 (97.5%) and 258 (91.5%) of these fields, respectively. We catalog the ~7 GHz radio continuum peak flux densities and positions of 80 previously-known and 298 candidate HII regions. After averaging ~18 RRL transitions, we detect 77 RRL velocity components towards 76 previously-known HII regions and 267 RRL velocity components towards 256 HII region candidates. The discovery of RRL emission from these nebulae increases the number of known Galactic HII regions in the surveyed zone by 82%, to 568 nebulae. In the fourth quadrant we discover 50 RRLs with positive velocities, placing those sources outside the Solar circle. Including the pilot survey, the SHRDS has now discovered 295 Galactic HII regions. In the next data release we expect to add ~200 fainter and more distant nebulae., 113 pages, 15 figures, 11 tables (at the end); accepted for publication in ApJS

Feedback from massive stars plays a critical role in the evolution of the Universe by driving powerful outflows from galaxies that enrich the intergalactic medium and regulate star formation. An important source of outflows may be the most numerous galaxies in the Universe: dwarf galaxies. With small gravitational potential wells, these galaxies easily lose their star-forming material in the presence of intense stellar feedback. Here, we show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming bar of the galaxy. The outflows are cold, $T, Published in Nature Astronomy, 29 October 2018, http://dx.doi.org/10.1038/s41550-018-0608-8

We identify a counterpart to a Galactic supershell in diffuse radio polarisation, and use this to determine the magnetic fields associated with this object. GSH 006$-$15$+$7 has perturbed the polarised emission at 2.3$\,$GHz, as observed in the S-band Polarisation All Sky Survey (S-PASS), acting as a Faraday screen. We model the Faraday rotation over the shell, and produce a map of Faraday depth over the area across it. Such models require information about the polarised emission behind the screen, which we obtain from the Wilkinson Microwave Anisotropy Probe (WMAP), scaled from 23$\,$GHz to 2.3$\,$GHz, to estimate the synchrotron background behind GSH 006$-$15$+$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 $|B_\parallel|_\text{peak} = 2.0\substack{+0.01 \\ -0.7}\,\mu$G. Our measurement probes weak magnetic fields in a low-density regime (number densities of $\sim0.4\,$cm$^{-3}$) of the ISM, thus providing crucial information about the magnetic fields in the partially-ionised phase., Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 19 pages, 19 figures

HI self absorption (HISA) clouds are clumps of cold neutral hydrogen (HI) visible in front of warm background gas, which makes them ideal places to study the properties of the cold atomic component of the interstellar medium (ISM). The Riegel-Crutcher (R-C) cloud is the most striking HISA feature in the Galaxy. It is one of the closest HISA clouds to us and is located in the direction of the Galactic Centre, which provides a bright background. High-resolution interferometric measurements have revealed the filamentary structure of this cloud, however it is difficult to accurately determine the temperature and the density of the gas without optical depth measurements. In this paper we present new HI absorption observations with the Australia Telescope Compact Array (ATCA) against 46 continuum sources behind the Riegel-Crutcher cloud to directly measure the optical depth of the cloud. We decompose the complex HI absorption spectra into Gaussian components using an automated machine learning algorithm. We find 300 Gaussian components, from which 67 are associated with the R-C cloud (0 < v_{LSR} < 10 kms, FWHM < 10 kms). Combining the new HI absorption data with HI emission data from previous surveys we calculate the spin temperature and find it to be between 20 and 80 K. Our measurements uncover a temperature gradient across the cloud with spin temperatures decreasing towards positive Galactic latitudes. We also find three new OH absorption lines associated with the cloud, which support the presence of molecular gas., Accepted to MNRAS, 27 pages, 26 figures, 7 tables

Hydroxyl (OH) is expected to be abundant in diffuse interstellar molecular gas as it forms along with $H_2$ under similar conditions and within a similar extinction range. We have analyzed absorption measurements of OH at 1665 MHz and 1667 MHz toward 44 extragalactic continuum sources, together with the J=1-0 transitions of $^{12}$CO, $^{13}$CO , and C$^{18}$O, and the J=2-1 of $^{12}$CO. The excitation temperature of OH were found to follow a modified log-normal distribution, $ f(T{\rm_{ex}}) \propto \frac{1}{ \sqrt{2\pi}\sigma } \rm{exp}\left[-\frac{[ln(\textit{T}_{ex})-ln(3.4\ K)]^2}{2\sigma^2}\right] $, the peak of which is close to the temperature of the Galactic emission background (CMB+synchron). In fact, 90% of the OH has excitation temperature within 2 K of the Galactic background at the same location, providing a plausible explanation for the apparent difficulty to map this abundant molecule in emission. The opacities of OH were found to be small and peak around 0.01. For gas at intermediate extinctions (A$\rm_V$ $\sim$ 0.05-2 mag), the detection rate of OH with detection limit $N(\mathrm{OH})\simeq 10^{12}$ cm$^{-2}$ is approximately independent of $A\rm_V$. We conclude that OH is abundant in the diffuse molecular gas and OH absorption is a good tracer of `dark molecular gas (DMG)'. The measured fraction of DMG depends on assumed detection threshold of the CO data set. The next generation of highly sensitive low frequency radio telescopes, FAST and SKA, will make feasible the systematic inventory of diffuse molecular gas, through decomposing in velocity the molecular (e.g. OH and CH) absorption profiles toward background continuum sources with numbers exceeding what is currently available by orders of magnitude., Comment: 24 pages, 23 figures. Accepted for publication in ApJS

We present 21-cm Spectral Line Observations of Neutral Gas with the VLA (21-SPONGE), a Karl G. Jansky Very Large Array (VLA) large project (~600 hours) for measuring the physical properties of Galactic neutral hydrogen (HI). 21-SPONGE is distinguished among previous Galactic HI studies as a result of: (1) exceptional optical depth sensitivity ($\sigma_{\tau} < 10^{-3}$ per $0.42\rm\,km\,s^{-1}$ channels over 57 lines of sight); (2) matching 21 cm emission spectra with highest-possible angular resolution (~4') from the Arecibo Observatory; (3) detailed comparisons with numerical simulations for assessing observational biases. We autonomously decompose 21 cm spectra and derive the physical properties (i.e., spin temperature, $T_s$, column density) of the cold neutral medium (CNM; $T_s 1000\rm\,K$) simultaneously. We detect 50% of the total HI mass in absorption, the majority of which is CNM (56 +/- 10%, corresponding to 28% of the total HI mass). Although CNM is detected ubiquitously, the CNM fraction along most lines of sight is, Comment: 33 pages, 22 figures, 5 tables; ApJ submitted

As pulsars lose energy, primarily in the form of magnetic dipole radiation, their rotation slows down accordingly. For some pulsars, this spin-down is interrupted by occasional abrupt spin-up events known as glitches 1 . A glitch is hypothesized to be a catastrophic release of pinned vorticity 2 that provides an exchange of angular momentum between the superfluid outer core and the crust. This is manifested by a minute alteration in the rotation rate of the neutron star and its co-rotating magnetosphere, which is revealed by an abrupt change in the timing of observed radio pulses. Measurement of the flux density, polarization and single-pulse arrival times of the glitch with high time resolution may reveal the equation of state of the crustal superfluid, its drag-to-lift ratio and the parameters that describe its friction with the crust 3 . This has not hitherto been possible because glitch events happen unpredictably. Here we report single-pulse radio observations of a glitch in the Vela pulsar, which has a rotation frequency of 11.2 hertz. The glitch was detected on 2016 December 12 at 11:36 universal time, during continuous observations of the pulsar over a period of three years. We detected sudden changes in the pulse shape coincident with the glitch event: one pulse was unusually broad, the next pulse was missing (a ‘null’) and the following two pulses had unexpectedly low linear polarization. This sequence was followed by a 2.6-second interval during which pulses arrived later than usual, indicating that the glitch affects the magnetosphere.

The Fan Region is one of the dominant features in the polarized radio sky, long thought to be a local (distance < 500 pc) synchrotron feature. We present 1.3-1.8 GHz polarized radio continuum observations of the region from the Global Magneto-Ionic Medium Survey (GMIMS) and compare them to maps of Halpha and polarized radio continuum intensity from 0.408-353 GHz. The high-frequency (> 1 GHz) and low-frequency (< 600 MHz) emission have different morphologies, suggesting a different physical origin. Portions of the 1.5 GHz Fan Region emission are depolarized by about 30% by ionized gas structures in the Perseus Arm, indicating that this fraction of the emission originates >2 kpc away. We argue for the same conclusion based on the high polarization fraction at 1.5 GHz (about 40%). The Fan Region is offset with respect to the Galactic plane, covering -5�� < b < +10��; we attribute this offset to the warp in the outer Galaxy. We discuss origins of the polarized emission, including the spiral Galactic magnetic field. This idea is a plausible contributing factor although no model to date readily reproduces all of the observations. We conclude that models of the Galactic magnetic field should account for the > 1 GHz emission from the Fan Region as a Galactic-scale, not purely local, feature., Accepted to MNRAS

The Southern HII Region Discovery Survey (SHRDS) is a survey of the third and fourth quadrants of the Galactic plane that will detect radio recombination line and continuum emission at cm-wavelengths from several hundred HII region candidates using the Australia Telescope Compact Array. The targets for this survey come from the WISE Catalog of Galactic HII Regions, and were identified based on mid-infrared and radio continuum emission. In this pilot project, two different configurations of the Compact Array Broad Band receiver and spectrometer system were used for short test observations. The pilot surveys detected radio recombination line emission from 36 of 53 HII region candidates, as well as seven known \hii regions that were included for calibration. These 36 recombination line detections confirm that the candidates are true HII regions, and allow us to estimate their distances., Comment: 19 pages, 5 figures, Astronomical Journal in press

We investigate the kinematics of neutral gas in the Small Magellanic Cloud (SMC) and test the hypothesis that it is rotating in a disk. To trace the 3D motions of the neutral gas distribution, we identify a sample of young, massive stars embedded within it. These are stars with radial velocity measurements from spectroscopic surveys and proper motion measurements from Gaia, whose radial velocities match with dominant HI components. We compare the observed radial and tangential velocities of these stars with predictions from the state-of-the-art rotating disk model based on high-resolution 21 cm observations of the SMC from the Australian Square Kilometer Array Pathfinder telescope. We find that the observed kinematics of gas-tracing stars are inconsistent with disk rotation. We conclude that the kinematics of gas in the SMC are more complex than can be inferred from the integrated radial velocity field. As a result of violent tidal interactions with the LMC, non-rotational motions are prevalent throughout the SMC, and it is likely composed of distinct sub-structures overlapping along the line of sight., 9 pages, 5 figures, 1 Appendix; ApJ accepted

Observations of the frequencies of different rotational transitions of the methanol molecule have provided the most sensitive probe to date for changes in the proton-to-electron mass ratio, over space and time. Using methanol absorption detected in the gravitational lens system PKS B1830-211, changes in the proton-to-electron ratio over the last 7.5 billion years have been constrained to a fractional change less than 1.1e-07. Molecular absorption systems at cosmological distances present the best opportunity for constraining or measuring changes in the fundamental constants of physics over time, however, we are now at the stage where potential differences in the morphology of the absorbing systems and the background source, combined with their temporal evolution, provide the major source of uncertainty in some systems. Here we present the first milliarcsecond resolution observations of the molecular absorption system towards PKS B1830-211. We have imaged the absorption from the 12.2-GHz transition of methanol (which is redshifted to 6.45 GHz) toward the southwestern component and show that it is possibly offset from the peak of the continuum emission and partially resolved on milliarcsecond scales. Future observations of other methanol transitions with similar angular resolution offer the best prospects for reducing systematic errors in investigations of possible changes in the proton-to-electron mass ratio on cosmological scales., 8 pages, 3 figures, accepted for publication in MNRAS

We analyze synthetic neutral hydrogen (HI) absorption and emission spectral lines from a high- resolution, three-dimensional hydrodynamical simulation to quantify how well observational methods recover the physical properties of interstellar gas. We present a new method for uniformly decomposing HI spectral lines and estimating the properties of associated gas using the Autonomous Gaussian Decomposition (AGD) algorithm. We find that Hi spectral lines recover physical structures in the simulation with excellent completeness at high Galactic latitude, and this completeness declines with decreasing latitude due to strong velocity-blending of spectral lines. The temperature and column density inferred from our decomposition and radiative transfer method agree with the simulated values within a factor of < 2 for the majority of gas structures. We next compare synthetic spectra with observations from the 21-SPONGE survey at the Karl G. Jansky Very Large Array using AGD. We find more components per line of sight in 21-SPONGE than in synthetic spectra, which reflects insufficient simulated gas scale heights and the limitations of local box simulations. In addition, we find a significant population of low-optical depth, broad absorption components in the synthetic data which are not seen in 21-SPONGE. This population is not obvious in integrated or per-channel diagnostics, and reflects the benefit of studying velocity-resolved components. The discrepant components correspond to the highest spin temperatures (1000 < Ts < 4000 K), which are not seen in 21-SPONGE despite sufficient observational sensitivity. We demonstrate that our analysis method is a powerful tool for diagnosing neutral ISM conditions, and future work is needed to improve observational statistics and implementation of simulated physics., Accepted for publication in ApJ. Revised to incorporate referee comments. 18 pages, 18 figures, 1 table

The mechanisms of emission and changes in rotation frequency ('glitching') of the Vela pulsar (J0835-4510) are not well understood. Further insight into these mechanisms can be achieved by long-term studies of integrated pulse width, timing residuals, and bright pulse rates. We have undertaken an intensive observing campaign of Vela and collected over 6000 hours of single pulse data. The data shows that the pulse width changes with time, including marked jumps in width after micro-glitches (frequency changes). The abundance of bright pulses also changes after some micro-glitches, but not all. The secular changes in pulse width have three possible cyclic periods, that match with X-ray periodicities of a helical jet that are interpreted as free precession., Comment: 6 pages, 8 figures. Accepted for publication in The Astrophysical Journal

Using atomic hydrogen (HI) data from the VLA Galactic Plane Survey we measure the HI terminal velocity as a function of longitude for the first quadrant of the Milky Way. We use these data, together with our previous work on the fourth Galactic quadrant, to produce a densely sampled, uniformly measured, rotation curve of the Northern and Southern Milky Way between $3~{\rm kpc} < R < 8~{\rm kpc}$. We determine a new joint rotation curve fit for the first and fourth quadrants, which is consistent with the fit we published in McClure-Griffiths \& Dickey (2007) and can be used for estimating kinematic distances interior to the solar circle. Structure in the rotation curves is now exquisitely well defined, showing significant velocity structure on lengths of $\sim 200$ pc, which is much greater than the spatial resolution of the rotation curve. Furthermore, the shape of the rotation curves for the first and fourth quadrants, even after subtraction of a circular rotation fit shows a surprising degree of correlation with a roughly sinusoidal pattern between $4.2 < R < 7$ kpc., 24 pages, 8 figures. Accepted for publication in the Astrophysical Journal

The role of large-scale stellar feedback in the formation of molecular clouds has been investigated observationally by examining the relationship between HI and 12CO(J=1-0) in supershells. Detailed parsec-resolution case studies of two Milky Way supershells demonstrate an enhanced level of molecularisation over both objects, and hence provide the first quantitative observational evidence of increased molecular cloud production in volumes of space affected by supershell activity. Recent results on supergiant shells in the LMC suggest that while they do indeed help to organise the ISM into over-dense structures, their global contribution to molecular cloud formation is of the order of only ~10%., Comment: Proceedings of IAUS 292 - Molecular Gas, Dust, and Star Formation in Galaxies, eds. T. Wong & J. Ott. 4 pages, 3 figures

The astrophysical drivers for far-infrared spectroscopy of the Galactic interstellar medium using a 15m class telescope on Dome A are compelling. For the diffuse, atomic phase, the most important lines in the far-IR spectrum are OIat 63μm and CIIat 158μm. These are the dominant cooling lines of the cool, neutral medium, and they show rich spectral structure in Herschel observations at low latitudes. But theory predicts that they should both be highly sub-thermal in excitation, so that the level populations are not in equilibrium with the kinetic temperature of the gas. A large single dish telescope or an interferometer may be able to study the absorption and emission to determine the optical depth and column density of atoms and the physical conditions in the emission regions. Comparison of Herschel CIIspectra with 21-cm absorption spectra indicates that a significant fraction of the 158μm flux may be coming from the atomic rather than the molecular phase.

Using HI absorption spectra taken from the recent surveys of λ 21-cm line and continuum emission in the Galactic plane, the distribution of cool atomic clouds in the outer disk of the Milky Way is revealed. The warp of the midplane is clearly seen in absorption, as it is in emission, and the cool, neutral medium also shows flaring or increase in scale height with radius similar to that of the warm atomic hydrogen. The mixture of phases, as measured by the fraction of HI in the cool clouds relative to the total atomic hydrogen, stays nearly constant from the solar circle out to about 25 kpc radius. Assuming cool phase temperature ∼50 K this indicates a mixing ratio of 15% to 20% cool HI, with the rest warm.

The papers in this volume represent a broad spectrum of observational, theoretical, and computational astrophysics, sharing as a unifying core the Disk-Halo Interaction in the Milky Way and other spiral galaxies. This topic covers a wide range of Galactic and extragalactic research, built on a foundation of numerous and diverse physical processes. This summary groups the papers according to six themes, with some historical background and finally a look to the future. The final message is that the astrophysical techniques discussed and reviewed at this conference will grow over the next decade to answer even more fundamental questions about galaxy evolution and the history of the universe.

Rotation measures of pulsars and extragalactic point sources have been known to reveal large-scale antisymmetries in the Faraday rotation sky with respect to the Galactic plane and halo that have been interpreted as signatures of the mean magnetic field in the Galactic halo. We describe Faraday rotation measurements of the diffuse Galactic polarized radio emission over a large region in the northern Galactic hemisphere. Through application of Rotation Measure Synthesis we achieve sensitive Faraday rotation maps with high angular resolution, capable of revealing fine-scale structures of about 1 deg in the Faraday rotation sky. Our analysis suggests that the observed antisymmetry in the Faraday rotation sky at b > 0 deg is dominated by the magnetic field around a local HI bubble at a distance of approx. 100 pc, and not by the magnetic field of the Galactic halo. We derive physical properties of the magnetic field of this shell, which we find to be 20 - 34 uG strong. It is clear that the diffuse polarized radio emission contains important information about the local magneto-ionic medium, which cannot yet be derived from Faraday rotation measures of extragalactic sources or pulsars alone., Published in Astrophysical Journal Letters 724 (2010) L48-L52

Three recent surveys of 21-cm line emission in the Galactic plane, combining single dish and interferometer observations to achieve resolution of 1 arcmin to 2 arcmin, 1 km/s, and good brightness sensitivity, have provided some 650 absorption spectra with corresponding emission spectra for study of the distribution of warm and cool phase H I in the interstellar medium. These emission-absorption spectrum pairs are used to study the temperature of the interstellar neutral hydrogen in the outer disk of the Milky Way, outside the solar circle, to a radius of 25 kpc. The cool neutral medium is distributed in radius and height above the plane with very similar parameters to the warm neutral medium. In particular, the ratio of the emission to the absorption, which gives the mean spin temperature of the gas, stays nearly constant with radius to 25 kpc radius. This suggests that the mixture of cool and warm phases is a robust quantity, and that the changes in the interstellar environment do not force the H I into a regime where there is only one temperature allowed. The mixture of atomic gas phases in the outer disk is roughly 15% to 20% cool (40 K to 60 K), the rest warm, corresponding to mean spin temperature 250 to 400 K. The Galactic warp appears clearly in the absorption data, and other features on the familiar longitude-velocity diagram have analogs in absorption with even higher contrast than for 21-cm emission. In the third and fourth Galactic quadrants the plane is quite flat, in absorption as in emission, in contrast to the strong warp in the first and second quadrants. The scale height of the cool gas is similar to that of the warm gas, and both increase with Galactic radius in the outer disk., Comment: Accepted for Ap J and scheduled for 2009 March 1 volume 693. LaTeX 27 pages with 29 figures

In November 2006, the Australian Federal Government announced $15.8M in funding for geospatial research infrastructure through the National Collaborative Research Infrastructure Strategy (NCRIS). NCRIS is an initiative under the Australian Government?s Backing Australia?s Ability package with a number of key principles, including maximising the contributions of the R&D system to economic development, national security, social wellbeing and environmental sustainability. Here we outline why particular components of geospatial infrastructure are required in Australia to advance (equip) geospatial research over the next 20 years. We describe some of the scientific objectives that required an upgrade and densification of Australia?s geospatial infrastructure. This paper is the perspective of researchers from a subset of University researchers involved in the AuScope Geospatial component, and so does not necessarily encompass the opinions of all those involved in AuScope geospatial.

We have analyzed 793 atomic hydrogen emission and absorption spectrum pairs toward continuum background sources in the northern and southern Galactic plane. In this paper we focus on absorption features from cold gas in the outermost arms of the Galaxy. We find H I absorption associated on a global scale with the outer spiral arm (first and second Galactic quadrants). To a lesser extent we also see absorption associated with the most distant spiral arm in the third and fourth Galactic quadrants. In total, 236 spectra contain clear absorption features associated with the outermost spiral arms. Cool-phase gas therefore exists throughout these spiral arms. The mean distances between absorbing clouds are on the order of 90-220 pc. We identify a number of striking H I structures with masses on the order of 105-106 M⊙ containing cool H I gas with temperatures below 100 K. These clouds are only marginally stable against gravitational collapse.