We present the first interferometer map of the H 2 O maser emission in the active nucleus of NGC 4945, which exhibits both starburst and Seyfert qualities. Although the declination of the galaxy is −49 • , we were able to make the observations with the southernmost antennas of the Very Long Baseline Array. Strong maser emission is present in three velocity ranges, one near the systemic velocity and two shifted roughly symmetrically by ±(100 − 150) km s −1 . This is the first detection of highly blue-shifted water emission in NGC 4945. We also report a marginal detection of previously unreported red-shifted emission at a velocity of ∼ +200 km s −1 with respect to systemic. From fringe rate analysis we determined the position of the maser to be α 1950 = 13 h 02 m 32. s 28 ± 0. s 02; δ 1950 = −49 • 12 ′ 01. ′′ 9 ± 0. ′′ 1. The uncertainties in earlier estimates are at least several arcseconds. The maser lies within 2 ′′ (36 pc at a distance of 3.7 Mpc) of the peaks in 1.4 GHz continuum and 1.6 µm emission from the nucleus. The mappable maser emission is distributed roughly linearly over ≈ 40 milliarcseconds (0.7 pc) at a position angle of ≈ 45 • , which is close to the 43 ± 2 • position angle of the galactic disk. The red and blue-shifted emission symmetrically stradle the systemic emission on the sky, which suggests material in edge-on circular motion around a central object. The position-velocity structure indicates a binding mass of ∼ 1 × 10 6 M ⊙ , within a volume of radius ≈ 0.3 pc, which in combination with estimates of the AGN luminosity, implies that the central engine radiates on the order of 10% of its Eddington luminosity.

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The Large-Aperture Experiment to Detect the Dark Age (LEDA) was designed to detect the predicted O(100) mK sky-averaged absorption of the Cosmic Microwave Background by Hydrogen in the neutral pre-and intergalactic medium just after the cosmological Dark Age. The spectral signature would be associated with emergence of a diffuse Lyα background from starlight during 'Cosmic Dawn'. Recently, Bowman et al. (2018) have reported detection of this predicted absorption feature, with an unexpectedly large amplitude of 530 mK, centered at 78 MHz. Verification of this result by an independent experiment, such as LEDA, is pressing. In this paper, we detail design and characterization of the LEDA radiometer systems, and a first-generation pipeline that instantiates a signal path model. Sited at the Owens Valley Radio Observatory Long Wavelength Array, LEDA systems include the station correlator, five well-separated redundant dual polarization radiometers and backend electronics. The radiometers deliver a 30-85 MHz band (16 < z < 34) and operate as part of the larger interferometric array, for purposes ultimately of in situ calibration. Here, we report on the LEDA system design, calibration approach, and progress in characterization as of January 2016. The LEDA systems are currently being modified to improve performance near 78 MHz in order to verify the purported absorption feature.

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The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics -understanding how galaxies form -and astro-particle physics -inferring properties of the dark components.The Square Kilometre Array (SKA) will provide the only means of studying the cosmic evolution of neutral Hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the rôles of gas accretion and galaxy merging.'All hemisphere' HI redshift surveys to z ∼ 1.5 are feasible with wide-field-of-view realizations of the SKA and, by measuring the galaxy power spectrum in exquisite detail, will allow the first precise studies of the equationof-state of dark energy. The SKA will be capable of other uniquely powerful cosmological studies including the measurement of the dark-matter power spectrum using weak gravitational lensing, and the precise measurement of H0 using extragalactic water masers.The SKA is likely to become the premier dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST, SNAP) and other early-21 st -century datasets.

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We report the cumulative results of five surveys for H 2 O maser emission at 1.35 cm wavelength in 131 active galactic nuclei (AGNs) and star-forming galaxies, conducted at the Parkes Observatory between 1993 and 1998. We detected one new maser, in the edge-on galaxy IRAS F01063-8034, which exhibits a single, ∼ 0.1 Jy spectral feature at 4282 ± 6 km s −1 (heliocentric) with an unusually large 54 ± 16 km s −1 half-power full width. The centroid velocity of the emission increased to 4319.6 ± 0.6 km s −1 (38 ± 2 km s −1 width) over the 13 days between discovery and confirmation of the detection. A similarly broad linewidth and large change in velocity has been noted for the maser in NGC 1052, wherein jet activity excites the emission. Neither optical spectroscopy, radio-infrared correlations, nor infrared colors provide compelling evidence of unusual activity in the nucleus of IRAS F01063-8034. Since the galaxy appears to be outwardly normal at optical and infrared wavelengths, detection of an H 2 O maser therein is unique. The maser emission is evidence that the galaxy harbors an AGN that is probably obscured by the edge-on galactic disk. The detection highlights the possibility that undetected AGNs could be hidden in other relatively nearby