MeerKAT

Abstract:

The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper we present new 150-MHz observations carried out with the LOw Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6$\times$14.7 arcsec and reaches an rms of 160 $\mu$Jy beam$^{-1}$ at the centre of the field. As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of $\alpha_{150}^{1400}=-0.78\pm0.015$. The median spectral index becomes slightly flatter (increasing from $\alpha_{150}^{1400}=-0.84$ to $\alpha_{150}^{1400}=-0.75$) with decreasing flux density down to $S_{150} \sim$10 mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150 MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 Ultra-steep spectrum (USS) sources and 13 peaked spectrum sources. We estimate that up to 21 percent of these could have $z>4$ and are candidate high-$z$ radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects.

Abstract:

© Copyright owned by the author(s). Deep galaxy surveys have revealed that the global star formation rate (SFR) density in the universe peaks at 1≤ z ≤2 and sharply declines towards z = 0. But a clear picture of the underlying processes, in particular the evolution of cold atomic (∼100 K) and molecular gas phases, that drive such a strong evolution is yet to emerge. MALS is designed to use MeerKAT’s L- and UHF-band receivers to carry out the most sensitive (N(H I)>1019cm−2) dust-unbiased search of intervening H I 21-cm and OH 18-cm absorption lines at 0 < z < 2. This will provide reliable measurements of the evolution of cold atomic and molecular gas cross-sections of galaxies, and unravel the processes driving the steep evolution in the SFR density. The large sample of H I and OH absorbers obtained from the survey will (i) lead to tightest constraints on the fundamental constants of physics, and (ii) be ideally suited to probe the evolution of magnetic fields in disks of galaxies via Zeeman Splitting or Rotation Measure synthesis. The survey will also provide an unbiased census of H I and OH absorbers, i.e. cold gas associated with powerful AGNs (>1024W Hz−1) at 0 < z < 2, and will simultaneously deliver a blind H I and OH emission line survey, and radio continuum survey. Here, we describe the MALS survey design, observing plan and the science issues to be addressed under various science themes.

Abstract:

Deep galaxy surveys have revealed that the global star formation rate (SFR) density in the universe peaks at 1≤ z ≤2 and sharply declines towards z = 0. But a clear picture of the underlying processes, in particular the evolution of cold atomic (∼100 K) and molecular gas phases, that drive such a strong evolution is yet to emerge. MALS is designed to use MeerKAT’s L- and UHF-band receivers to carry out the most sensitive (N(H I)>1019 cm−2) dust-unbiased search of intervening H I 21-cm and OH 18-cm absorption lines at 0 < z < 2. This will provide reliable measurements of the evolution of cold atomic and molecular gas cross-sections of galaxies, and unravel the processes driving the steep evolution in the SFR density. The large sample of H I and OH absorbers obtained from the survey will (i) lead to tightest constraints on the fundamental constants of physics, and (ii) be ideally suited to probe the evolution of magnetic fields in disks of galaxies via Zeeman Splitting or Rotation Measure synthesis. The survey will also provide an unbiased census of H I and OH absorbers, i.e. cold gas associated with powerful AGNs (>1024 W Hz−1) at 0 < z < 2, and will simultaneously deliver a blind H I and OH emission line survey, and radio continuum survey. Here, we describe the MALS survey design, observing plan and the science issues to be addressed under various science themes.

Abstract:

The MIGHTEE large survey project will survey four of the most well-studied extragalactic deep fields, totalling 20 square degrees to $\mu$Jy sensitivity at Giga-Hertz frequencies, as well as an ultra-deep image of a single ~1 square degree MeerKAT pointing. The observations will provide radio continuum, spectral line and polarisation information. As such, MIGHTEE, along with the excellent multi-wavelength data already available in these deep fields, will allow a range of science to be achieved. Specifically, MIGHTEE is designed to significantly enhance our understanding of, (i) the evolution of AGN and star-formation activity over cosmic time, as a function of stellar mass and environment, free of dust obscuration; (ii) the evolution of neutral hydrogen in the Universe and how this neutral gas eventually turns into stars after moving through the molecular phase, and how efficiently this can fuel AGN activity; (iii) the properties of cosmic magnetic fields and how they evolve in clusters, filaments and galaxies. MIGHTEE will reach similar depth to the planned SKA all-sky survey, and thus will provide a pilot to the cosmology experiments that will be carried out by the SKA over a much larger survey volume.

Abstract:

The MIGHTEE large survey project will survey four of the most well-studied extragalactic deep fields, totalling 20 square degrees to µJy sensitivity at Giga-Hertz frequencies, as well as an ultra-deep image of a single ∼1 deg2 MeerKAT pointing. The observations will provide radio continuum, spectral line and polarisation information. As such, MIGHTEE, along with the excellent multi-wavelength data already available in these deep fields, will allow a range of science to be achieved. Specifically, MIGHTEE is designed to significantly enhance our understanding of, (i) the evolution of AGN and star-formation activity over cosmic time, as a function of stellar mass and environment, free of dust obscuration; (ii) the evolution of neutral hydrogen in the Universe and how this neutral gas eventually turns into stars after moving through the molecular phase, and how efficiently this can fuel AGN activity; (iii) the properties of cosmic magnetic fields and how they evolve in clusters, filaments and galaxies. MIGHTEE will reach similar depth to the planned SKA all-sky survey, and thus will provide a pilot to the cosmology experiments that will be carried out by the SKA over a much larger survey volume.