LADUMA

LADUMA
Name	LADUMA
Location	South Africa
Established	2015
Telescope names	MeerKAT
Wavelength	21-centimetre
Aperture	64 dishes
Operator	South African Radio Astronomy Observatory

LADUMA

LADUMA is a deep radio survey targeting 21-centimetre neutral hydrogen emission in the distant Universe, conducted with the MeerKAT array near Carnarvon, Northern Cape in South Africa. The project aims to measure the evolution of cold gas across cosmic time by observing a single deep field, combining long integrations, wide instantaneous bandwidth, and high spectral resolution to detect faint emission from galaxies at intermediate to high redshift. LADUMA complements optical and infrared surveys by linking neutral hydrogen measurements to galaxy properties catalogued by facilities such as Hubble Space Telescope, Spitzer Space Telescope, Very Large Telescope, and the Atacama Large Millimeter/submillimeter Array.

Background and objectives

LADUMA was conceived to address how baryonic reservoirs fuel star formation and structural growth from the present day back to lookback times of several billion years, leveraging the sensitivity of MeerKAT built by the South African Radio Astronomy Observatory as part of precursor efforts for the Square Kilometre Array. Primary objectives include constraining the cosmic evolution of the neutral hydrogen mass function, measuring the HI density parameter Omega_HI, and determining kinematic properties of HI in galaxies over redshift. The survey links to legacy programs and surveys such as COSMOS, CANDELS, Sloan Digital Sky Survey, Galaxy And Mass Assembly, DEEP2 Galaxy Redshift Survey, and observations by the James Webb Space Telescope to enable multiwavelength studies of gas, stars, and dust.

Survey design and methodology

LADUMA employs an ultra-deep integration strategy on a single target field selected for its low radio-frequency interference and extensive ancillary data, including catalogs from VISTA, GALEX, WISE, and Chandra X-ray Observatory. The survey uses MeerKAT's 64-dish configuration with high spectral flexibility to cover 21-cm emission across redshift ranges that map to frequencies from the L-band down to UHF, allowing HI detection from z ~ 0 to z ~ 1.4. Observational methodology combines long coherent integrations, RFI mitigation techniques developed with SKA South Africa, robust calibration using primary calibrators such as 3C 286 and PKS 1934-638, and imaging strategies like multi-scale CLEAN and direction-dependent calibration adopted from CASA workflows. Survey planning incorporated simulated source populations informed by semi-analytic models from groups working with Millennium Simulation outputs and hydrodynamic predictions from projects linked to Illustris and EAGLE.

Observations and data products

Observations consist of thousands of hours of on-source time producing spectral data cubes, continuum maps, source catalogs, and stacked spectra products. Data products released to the community include calibrated visibility datasets, HI line cubes with channel widths tuned to resolve galaxy kinematics, primary-beam-corrected continuum images, and derived catalogs of HI mass, linewidths, systemic velocities, and positional cross-matches to optical/IR counterparts from Hubble Space Telescope and ground-based surveys. Data reduction pipelines employed tools developed in collaboration with groups at University of Cape Town, Rhodes University, University of the Western Cape, and software packages like CASA, WSClean, and custom Python-based analysis frameworks interfacing with virtual observatory standards promoted by International Virtual Observatory Alliance. Ancillary data products include HI stacking outputs that coadd non-detections guided by spectroscopic redshifts from SAMI Galaxy Survey, GAMA, and zCOSMOS.

Key scientific results

LADUMA has produced constraints on the evolution of Omega_HI showing a slower decline with redshift than predicted by some semi-analytic models, prompting revisions to gas accretion and feedback prescriptions in simulations by teams associated with IllustrisTNG and other cosmological hydrodynamic projects. The survey yielded resolved HI kinematics for intermediate-redshift disk galaxies, enabling Tully–Fisher relation studies tied to angular momentum analyses comparable to work from THINGS and LITTLE THINGS. Stacking results provided statistical detections of HI in populations selected by stellar mass and star-formation rate drawn from CANDELS and COSMOS catalogs, while cross-correlation analyses between HI intensity maps and optical density fields connected LADUMA findings to large-scale structure results from BOSS and VIPERS. Observations uncovered gas-rich companions and tidal HI features linked to merger histories studied in relation to results from Sloan Digital Sky Survey imaging, and contributed to constraints on the baryon cycle when combined with molecular gas measurements from ALMA.

Collaborations and instrumentation

LADUMA is a consortium-driven project involving institutions across South Africa, United Kingdom, Netherlands, Germany, United States, Australia, and other countries, with key participation from South African Radio Astronomy Observatory, University of Cape Town, University of the Western Cape, Netherlands Institute for Radio Astronomy (ASTRON), and universities associated with the MeerKAT collaboration. Instrumentation centered on the MeerKAT array benefited from engineering teams linked to Square Kilometre Array Organisation and international partners providing backend correlators, high-performance computing, and data archiving solutions. Scientific coordination connected LADUMA to multiwavelength survey teams including COSMOS, CANDELS, GAMA, and radio surveys like MIGHTEE to maximize synergies and legacy value.

Legacy and impact on astronomy

LADUMA stands as a pathfinder for deep 21-cm science with next-generation facilities, informing observing strategies, calibration techniques, and survey designs for the Square Kilometre Array. Its public data releases, methodological innovations in deep HI stacking and RFI management, and cross-disciplinary datasets have influenced studies by researchers working on galaxy evolution, cosmic gas accretion, and angular momentum assembly, contributing to follow-on proposals and training of early-career scientists at institutions such as University of Oxford, University of Cambridge, Harvard University, and University of California, Berkeley. LADUMA's legacy will persist through integration with future SKA surveys and by anchoring empirical constraints used by theoretical groups refining models of baryon cycling across cosmic time.

Category:Astronomy projects