Astronomical widefield imaging of interferometric radio data is computationally expensive, especially for the large data volumes created by modern non-coplanar many-element arrays. We present a new widefield interferometric imager that uses the w-stacking algorithm and can make use of the w-snapshot algorithm. The performance dependencies of CASA's wprojection and our new imager are analysed and analytical functions are derived that describe the required computing cost for both imagers. On data from the Murchison Widefield Array, we find our new method to be an order of magnitude faster than w-projection, as well as being capable of full-sky imaging at full resolution and with correct polarisation correction. We predict the computing costs for several other arrays and estimate that our imager is a factor of 2-12 faster, depending on the array configuration. We estimate the computing cost for imaging the low-frequency Square-Kilometre Array observations to be 60 PetaFLOPS with current techniques. We find that combining w-stacking with the w-snapshot algorithm does not significantly improve computing requirements over pure w-stacking. The source code of our new imager is publicly released.

This paper describes the on-telescope performance of the Wide Field Spectrograph (WiFeS). The design characteristics of this instrument, at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) and mounted on the ANU 2.3 m telescope at the Siding Spring Observatory has been already described in an earlier paper (Dopita et al. in Astrophys. Space Sci. 310:255, 2007). Here we describe the throughput, resolution and stability of the instrument, and describe some minor issues which have been encountered. We also give a description of the data reduction pipeline, and show some preliminary results.

We measure the neutral atomic hydrogen (H I) gas content of field galaxies at intermediate redshifts of z ∼ 0.1 and z ∼ 0.2 using hydrogen 21-cm emission lines observed with the Westerbork Synthesis Radio Telescope (WSRT). In order to make high signal-to-noise ratio detections, an H I signal stacking technique is applied: H I emission spectra from multiple galaxies, optically selected by the CNOC2 redshift survey project, are co-added to measure the average H I mass of galaxies in the two redshift bins. We calculate the cosmic H I gas densities (Ω H I ) at the two redshift regimes and compare those with measurements at other redshifts to investigate the global evolution of the H I gas density over cosmic time. From a total of 59 galaxies at z ∼ 0.1 we find Ω H I = (0.33 ± 0.05)×10 −3 , and at z ∼ 0.2 we find Ω H I = (0.34 ± 0.09) × 10 −3 , based on 96 galaxies. These measurements help bridge the gap between high-z damped Lyman-α observations and blind 21-cm surveys at z = 0. We find that our measurements of Ω H I at z ∼ 0.1 and 0.2 are consistent with the H I gas density at z ∼ 0 and that all measurements of Ω H I from 21-cm emission observations at z 0.2 are in agreement with no evolution of the H I gas content in galaxies during the last 2.4 Gyr.

The Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) is a next-generation survey of neutral hydrogen (H I) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of 36 × 12-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radioquiet zone in Western Australia. WALLABY aims to survey three-quarters of the sky (−90 • < δ < +30 • ) to a redshift of z 0.26, and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam −1 per 4 km s −1 channel sensitivity. ASKAP's instantaneous field of view at 1.4 GHz, delivered by the PAF's 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five, WALLABY is expected to detect around half a million galaxies with a mean redshift of z ∼ 0.05 (∼200 Mpc). The scientific goals of WALLABY include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H I properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H I surveys. Combined with existing and new multi-wavelength sky surveys, WALLABY will enable an exciting new generation of panchromatic studies of the Local Universe. -First results from the WALLABY pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).

We use observations made with the Giant Metrewave Radio Telescope (GMRT) to probe the neutral hydrogen (H ) gas content of field galaxies in the VIMOS VLT Deep Survey (VVDS) 14h field at z ≈ 0.32. Because the H emission from individual galaxies is too faint to detect at this redshift, we use an H spectral stacking technique using the known optical positions and redshifts of the 165 galaxies in our sample to co-add their H spectra and thus obtain the average H mass of the galaxies. Stacked H measurements of 165 galaxies show that 95 per cent of the neutral gas is found in blue, star-forming galaxies. Among these galaxies, those having lower stellar mass are more gas-rich than more massive ones. We apply a volume correction to our H measurement to evaluate the H gas density at z ≈ 0.32 as Ω H I = (0.50 ± 0.18) × 10 −3 in units of the cosmic critical density. This value is in good agreement with previous results at z < 0.4, suggesting no evolution in the neutral hydrogen gas density over the last ∼4 Gyr. However the z ≈ 0.32 gas density is lower than that at z ∼ 5 by at least a factor of two.

Abstract. J, H and K images obtained with the Canada-France-Hawaii Telescope were used to investigate the stellar contents of the asymptotic giant branch (AGB) in the dwarf elliptical galaxy NGC 185. The bright parts of (K, J − K) and (K, H − K) color−magnitude diagrams consist of a group of bright blue stars, a dominant population of M-giants and a red C star population. There were 73 C stars with a mean magnitude of K = 16.26 ± 0.38, corresponding to M K = −7.93, and mean colors of (J − K) 0 = 2.253 and (H − K) 0 = 0.865. The number ratio of C stars to M-giants was estimated to be 0.11 ± 0.04 without any radial gradient from the center of NGC 185. The (J − K) and (H − K) color distributions of AGB stars showed an M-giant peak and blue and red tails, where the latter two correspond to AGB stars younger than those along M-giant peak and C stars. The bolometric luminosity functions of M-giants and C stars indicate that the M-giant AGB sequence has terminated at M bol = −6.2, while the most luminous C star has M bol = −5.5. The bolometric luminosity function of C stars in NGC 185 is very similar to that of recent literature values derived from Vi band photometry. The logarithmic slope of the luminosity function for bright M-giant stars was estimated to be 0.83 ± 0.02 in K band. Theoretical isochrone models, compared with the observed nearinfrared photometric properties of AGB stars, indicate that star formation in NGC 185 has a wide range of ages with possibly two different epochs of star formation.

We present the results of H I spectral stacking analysis of Giant Metrewave Radio Telescope (GMRT) observations targeting the COSMOS field. The GMRT data cube contains 474 field galaxies with redshifts known from the zCOSMOS-bright 10k catalogue. Spectra for the galaxies are co-added and the stacked spectrum allows us to make a ∼ 3σ measurement of the average H I mass. Using this average H I mass along with the integral optical B-band luminosity of the galaxies and the luminosity density of the COSMOS field, a volume normalisation is applied to obtain the cosmic H I mass density (Ω H I ). We find a cosmic H I mass density of Ω H I = (0.42 ± 0.16) × 10 −3 at z ∼ 0.37, which is the highest-redshift measurement of Ω H I ever made using H I spectral stacking. The value we obtained for Ω H I at z ∼ 0.37 is consistent with that measured from large blind 21-cm surveys at z = 0 as well as measurements from other H I stacking experiments at lower redshifts. Our measurement in conjunction with earlier measurements indicates that there has been no significant evolution of H I gas abundance over the last 4 Gyr. A weighted mean of Ω H I from all 21-cm measurements at redshifts z 0.4 gives Ω H I = (0.35 ± 0.01) × 10 −3 . The Ω H I measured (from H I 21-cm emission measurements) at z 0.4 is however approximately half that measured from Damped Lyman-α Absorption (DLA) systems at z 2. Deeper surveys with existing and upcoming instruments will be critical to understand the evolution of Ω H I in the redshift range intermediate between z ∼ 0.4 and the range probed by DLA observations.

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. 1 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. 1, 2 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 < 400 K, and may have formed during a period of active star formation 25 − 60 million years (Myr) ago. 3,4 The total mass of atomic gas in the outflow is ∼ 10 7 solar masses, M , or ∼ 3% of the total atomic gas of the galaxy. The inferred mass flux in atomic gas alone,Ṁ HI ∼ 0.2 − 1.0 M yr −1 , is up to an order of magnitude greater than the star formation rate. We suggest that most of the observed outflow will be stripped from the SMC through its interaction with its companion, the Large Magellanic Cloud (LMC), and the Milky Way, feeding the Magellanic Stream of hydrogen encircling the Milky Way.The SMC, at a distance of 60 kpc, 5 provides an excellent laboratory to study feedback in an interacting gas-rich dwarf galaxy with sensitivity and resolution that is unattainable almost anywhere else in the Universe. Using Australian SKA Pathfinder (ASKAP) commissioning data in the 21-cm line of atomic hydrogen (H I) we have imaged the SMC at 35 × 27 resolution across a 5.3 • × 5 • field-of-view, revealing extensive cold gas outflows from the galaxy. An image of the peak H I brightness is shown in Figure 1. The resolution of this image is the highest ever achieved in H I on this field, revealing features that are arXiv:1811.01772v1 [astro-ph.GA] 5 Nov 2018 ten times smaller in area than previous images. The gaseous structure of the main body of the SMC is described by two dominant regions as marked on Figure 1: the so-called bar, extending from the north to the south-west, and containing the majority of the dense gas and star formation and the wing, which extends in the direction of the LMC. 6 The bar, as traced by Cepheid variables, is extended along the line-of-sight with the closest part to the north at a distance of 57 − 63 kpc and containing the younger stars (< 150 Myr), with the south-western region at > 63 kpc and older. 5Our data have revealed an extensive network of exo-galactic H I features at distances up to 2 kpc from the main body of the SMC. These features are both spatially and kinematically anomalous. They can be characterized into three loose categories: comet-shaped head-tail clouds; enormous looping H I filaments; and compact high-velocity clouds at velocities deviating up to 65 km s −1 with respect to the rest of the SMC emission. The majority of these features lie to the North-West and North-East, with comparatively little exo-galactic structure to the South,...