The Five-hundred-meter Aperture Spherical radio Telescope (FAST) was completed with its main structure installed on September 25, 2016, after which it entered the commissioning phase. This paper aims to introduce the commissioning progress of the FAST over the past two years. To improve its operational reliability and ensure effective observation time, FAST has been equipped with a real-time information system for the active reflector system and hierarchical commissioning scheme for the feed support system, which ultimately achieves safe operation of the two systems. For meeting the high-performance indices, a high-precision measurement system was set up based on the effective control methods that were implemented for the active reflector system and feed support system. Since the commissioning of the FAST, a low-frequency ultra-wideband receiver and 19-beam 1.05-1.45 GHz receiver have been mainly used. Telescope efficiency, pointing accuracy, and system noise temperature were completely tested and ultimately achieved the acceptance indices of the telescope. The FAST has been in the process of national acceptance preparations and has begun to search for pulsars. In the future, it will still strive to improve its capabilities and expand its application prospects.

Commissioning progress of the FAST

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 \times12-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. wallaby aims to survey three-quarters of the sky (-90^{\circ} < \delta< +30^{\circ}) to a redshift of z \lesssim0.26, 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 \sim0.05 (∼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).

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WALLABY – an SKA Pathfinder H i survey

Neutral atomic hydrogen (HI) and molecular hydrogen (H2) play a primordial role in the cosmic evolution of galaxies. However, little is known about the co-evolution of these two gas phases. This discrepancy and the design of future telescopes like the SKA and ALMA require theoretical models of the joint evolution of HI and H2 in galaxies. This thesis starts with a phenomenological analysis of the H2/HI-ratios in a sample of 245 local galaxies. This analysis reveals a number of correlations between H2/HI-ratios and other galaxy properties, and we demonstrate that these correlations can be understood in terms of the microscopic relation between the H2/HI-ratio and the external gas pressure. We subsequently use this relation to derive an analytic model for the column densities of HI and H2 in arbitrary regular galaxies. As a second step, we apply the model for the column densities of HI and H2 to post-process approximately 3*10^7 virtual galaxies, whose cosmic evolution was simulated on the evolving dark matter skeleton output by the Millennium Simulation. The post-processing of these galaxies allows us to (i) split their total cold gas masses between HI, H2, and Helium, (ii) to assign realistic sizes to both the HI and H2-disks, and (iii) to evaluate the velocity profiles of HI and H2. The resulting hydrogen simulation successfully reproduces many local observations of HI and H2, such as mass functions (MFs), mass-diameter relations, and mass-velocity relations. A key prediction of this simulation is that the H2/HI-ratio of regular galaxies increases dramatically with redshift z, leading to a scaling of (1+z)^1.6 for the ratio between the cosmic space densities of H2 and HI. This prediction offers a unified explanation for (i) the weak evolution of the cosmic HI-density inferred from Lyman-alpha absorption against quasars, (ii) the large molecular masses detected in regular galaxies at z=1.5, and (iii) the recent cosmic decline in the density of star formation. As a third step, we introduce a heuristic model for the conversion of H2-masses into observable CO-line luminosities for galaxies at all redshifts. We apply this model to our hydrogen simulation in order to predict the luminosity functions of the first 10 rotational transitions of CO in galaxies at redshift z=0 to z=10. As a final step, we transform the simulated catalog of 3*10^7 evolving galaxies into a virtual observing cone, i.e. a catalog that lists the apparent HI and CO-line fluxes and corresponding line widths of millions of galaxies in a sky field with a comoving diameter of 500 Mpc/h. This catalog represents a tangible contribution towards the design and operation of future telescopes, such as the SKA and ALMA.

The Cosmic Evolution of Atomic and Molecular Hydrogen in Galaxies

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) passed national acceptance and is taking pilot cycle of 'Shared-Risk' observations. The 19-beam receiver covering 1.05-1.45 GHz was used for most of these observations. The electronics gain fluctuation of the system is better than 1\% over 3.5 hours, enabling enough stability for observations. Pointing accuracy, aperture efficiency and system temperature are three key parameters of FAST. The measured standard deviation of pointing accuracy is 7.9$''$, which satisfies the initial design of FAST. When zenith angle is less than 26.4$^\circ$, the aperture efficiency and system temperature around 1.4 GHz are $\sim$ 0.63 and less than 24 K for central beam, respectively. The measured value of these two parameters are better than designed value of 0.6 and 25 K, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral HI observations toward N672 and polarization observations toward 3C286. The performance allows FAST to take sensitive observations in various scientific goals, from studies of pulsar to galaxy evolution.

The fundamental performance of FAST with 19-beam receiver at L band

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Fast Radio Burst Energetics and Detectability from High Redshifts

Having achieved "first light" immediately prior to the ceremony introducing it on 25 September 2016, China's 500-m aperture spherical radio telescope (FAST) is now being kept busy with commissions. Its innovative design requires ~1,000 points to be measured and driven instead of just the two axes of motion, e.g., azimuth and elevation for most conventional antennas, to realize pointing and tracking. We have devised a survey plan to exploit the full sensitivity of FAST, while minimizing the complexities involved during system operation. The 19-beam L-band focal plan array will be rotated to specific angles and receive continuous data streams, while the surface shape and the focal cabin stay fixed. Such a survey will cover the northern sky in about 220 full days. Our aim is to obtain data simultaneously for pulsar search, detection of neutral hydrogen (HI) galaxies, HI imaging, and radio transients through multiple back ends. These data sets could represent a significant contribution to all related fields in radio astronomy and remain relevant for decades.

FAST in Space: Considerations for a Multibeam, Multipurpose Survey Using China's 500-m Aperture Spherical Radio Telescope (FAST)

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is expected to complete its commissioning in 2019. FAST will soon begin the Commensal Radio Astronomy FasT Survey (CRAFTS), a novel and unprecedented commensal drift scan survey of the entire sky visible from FAST. The goal of CRAFTS is to cover more than 20000 deg$^{2}$ and reach redshift up to about 0.35. We provide empirical measurements of the beam size and sensitivity of FAST across the 1.05 to 1.45 GHz frequency range of the FAST L-band array of 19-beams (FLAN). Using a simulated HI-galaxy catalogue based on the HI Mass Function (HIMF), we estimate the number of galaxies that CRAFTS may detect. At redshifts below 0.35, over $6\\,~\\times~\\,~10^{5}$ HI galaxies may be detected. Below the redshift of 0.07, the CRAFTS HIMF will be complete above a mass threshold of $10^{9.5}M_{\\odot}$. FAST will be able to investigate the environmental and redshift dependence of the HIMF to an unprecedented depth, shedding light onto the missing baryon and missing satellite problems.

Marko Krco

Papers

FAST in Space: Considerations for a Multibeam, Multipurpose Survey Using China's 500-m Aperture Spherical Radio Telescope (FAST)

Status and perspectives of the CRAFTS extra-galactic HI survey