astro-legacy-archive/eda2-159mhz

EDA2 159 MHz Southern-Sky Maps

This dataset contains four products from the EDA2 159 MHz southern-sky survey: maps made with and without a large-scale sky prior, a noise map, and a spectral-index map against the Haslam 408 MHz survey. The two intensity maps and the noise map cover the complete HEALPix grid; the spectral-index map has 279 pixels carrying the source HEALPix UNSEEN value.

Intended uses

The maps support low-frequency sky and foreground studies, including comparison with the 408 MHz sky and assessment of the large angular scales that a compact interferometer cannot measure directly. The EDA2_159MHz_I_noPrior_HPXbin is made without a spatial prior, while EDA2_159MHz_I_wPrior_HPXbin supplies the unmeasured harmonics from a rescaled, desourced and destriped Haslam map.

Instrument	EDA2, 256 dipoles, SKA-Low prototype
Site	Murchison Radio-astronomy Observatory, Western Australia
Centre frequency	159.375 MHz
Bandwidth	0.926 MHz
Observations	Drift scans on 2019-09-16/17 and 2020-04-10/11
Flux scale	Quiet Sun, 56,195 Jy at 159.375 MHz
Pixelisation	HEALPix, NSIDE 64 (49,152 pixels), RING ordering
Coordinate frame	Equatorial
Maximum resolution	Approximately 3.1 degrees on a 0.916-degree pixel grid

How to use

python -m venv .venv && .venv/bin/pip install datasets huggingface_hub pyarrow

from datasets import load_dataset
dataset = load_dataset("astro-legacy-archive/eda2-159mhz", "EDA2_159MHz_I_wPrior_HPXbin", split="train")
measurement = dataset.select([35]).select_columns(["T"])[0]
print(measurement["T"][573])

8815.318359375

The coordinate lookup is at Sgr A*. It returns the global maximum of this map. The corresponding maximum without the prior is 8626.316 K.

import json
from huggingface_hub import hf_hub_download
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/eda2-159mhz", "EDA2_159MHz_I_wPrior_HPXbin.parquet", repo_type="dataset")
print(json.loads(pq.read_schema(path).metadata[b"healpix_map"])["healpix"]["ordering"])

RING

Configs

Each source file contains one bintable and is addressed by its filename stem verbatim. Every table contains 48 rows of 1,024 pixels. The Parquets are about 0.3 MB each.

config	source file	content	unit
EDA2_159MHz_I_noPrior_HPXbin	EDA2_159MHz_I_noPrior_HPXbin.fits	Map made without a spatial prior, with a 247 K global monopole	K
EDA2_159MHz_I_wPrior_HPXbin	EDA2_159MHz_I_wPrior_HPXbin.fits	Full sky with unmeasured harmonics constrained by the Haslam prior	K
noise_map_HPXbin	noise_map_HPXbin.fits	Terrestrial and common-mode noise estimate	K
EDA2prior159_Haslam408_SI_HPXbin	EDA2prior159_Haslam408_SI_HPXbin.fits	159/408 MHz temperature spectral index	dimensionless

Dataset structure

Every config has one source column:

column	type	unit	description
T	fixed-size list[1024] of float32	config-dependent	Map value described in the config table above

Unit K is machine-readable with product-documentation provenance for both intensity maps and the noise map; the spectral index is dimensionless.

product file	coded pixels	range	median
EDA2_159MHz_I_noPrior_HPXbin	0	137.38297 to 8626.316 K	280.47 K
EDA2_159MHz_I_wPrior_HPXbin	0	167.29546 to 8815.318 K	320.80 K
noise_map_HPXbin	0	-1.0158879 to 1.0837861 K	0 K
EDA2prior159_Haslam408_SI_HPXbin	279	2.1404643 to 3.1088538	2.68267

The EDA2_159MHz_I_noPrior_HPXbin map, made without a spatial prior, covers the EDA2 sky below about +60 degrees declination and has a 247 K global monopole added for the largest scale that EDA2 cannot measure. The EDA2_159MHz_I_wPrior_HPXbin map covers the full sky; its unmeasured harmonics are constrained by a rescaled, desourced and destriped Haslam 408 MHz prior.

The noise map has exactly 4,900 zero pixels, precisely the pixels north of declination +53.57 degrees. It also contains 22,085 negative pixels; negative values are part of the noise estimate, not errors.

The spectral-index map's 279 UNSEEN values are a bright-source mask, not survey coverage. They form exactly nine compact discs: Cen A (102 pixels), Cyg A (57), Fornax A (25), Virgo A (23), Hydra A (16), Pictor A (15), 3C 353 (15), Her A (13), and one centred at RA 241.17, Dec +0.73 (13). Its observed fraction is 0.9943. Its sign convention is positive beta with T proportional to nu^(-beta), not the usual negative-alpha convention.

The spectral-index source value is float32 -1.6375e30. It remains in-band in the Parquet, so a naive mean is meaningless. Its value is recorded in coverage.codes and must be excluded before calculating a mean. The code is byte-identical to healpy.UNSEEN, documented as the special value used for masked pixels.

Provenance

• Canonical deposit: Dataset: EDA2 159 MHz All-Sky Radio Maps, version 1.0, published 2022-02-11.
• Deposit citation: "Mike Kriele (2022). Dataset: EDA2 159 MHz All-Sky Radio Maps. http://dx.doi.org/10.26185/620ee2ae9d8b7".
• On 2026-08-29, the four named HPXbin files in the DOI deposit and the NASA LAMBDA copy had the same SHA-256 digests.

source file	SHA-256
EDA2_159MHz_I_noPrior_HPXbin.fits	316786fd500793177f638a5e5306eb748989919b5401975ee2380dc534df7dd1
EDA2_159MHz_I_wPrior_HPXbin.fits	80bbd79e1dcfc24a38c7ddf3b9a241a695579609a5e26d922fc171946e6405bb
noise_map_HPXbin.fits	1d7f249f96e0f2da81f71ae3f3a92f12a1b0ab4a23f53dda00861d932accc038
EDA2prior159_Haslam408_SI_HPXbin.fits	eb9da6b68d88480612e4215091d829b57a45155801692e33b4f38006fbfac9db

The source maps retain RING ordering and identify the equatorial frame with COORDSYS = 'C'. The embedded pixel_rule maps row/list positions to source pixels. Provenance (the original headers, source URLs and hashes, retrieval date, and the regeneration command) is embedded in each Parquet file. Rebuild the dataset with python tools/make_eda2.py.

The deposit also contains HPX2D image duplicates of the same four maps; they are not imported here.

Considerations for use

• The EDA2_159MHz_I_noPrior_HPXbin map includes an added 247 K global monopole; the interferometer did not measure this largest angular scale.
• The EDA2_159MHz_I_wPrior_HPXbin result depends on its rescaled Haslam prior for unmeasured harmonics.
• The noise map's zeros and negative values have the meanings described above and are not missing-data markers.
• The spectral index uses positive beta in T proportional to nu^(-beta).
• Both intensity maps are poorly measured above declination +40 degrees, where the antenna response falls to approximately 5%; spectral indices above +40 degrees are not trustworthy.
• The intensity maps are confusion-limited. The total noise-map RMS over observed sky is 0.073 K, with a 0.24 K maximum near a known interference feature around RA 19-21h, Dec -26.7.
• Temperatures show a 10-25% excess around the south celestial pole.

Licensing and credit

The deposit's licence field says "Creative Commons Attribution" without a version. The paper is licensed CC BY 4.0, but no versioned licence is stated for the deposited data. The source's version-unspecified wording is represented as other rather than upgraded to a versioned identifier.

The paper acknowledges the Wajarri Yamatji People as the traditional owners of the Murchison Radio-astronomy Observatory site.

Citations

Please cite Kriele et al. (2022): Kriele, M. A., Wayth, R. B., Bentum, M. J., Juswardy, B., & Trott, C. M. 2022, PASA 39, e017, DOI 10.1017/pasa.2022.2.

Errata and requests

To report an erratum, propose a correction, or ask a question about this dataset, open a Discussion or Pull Request in its Community tab; posting requires a free Hugging Face account. Dataset requests and archive-wide questions may be posted in the README space's Community tab or the Community tab of any dataset. Confirmed corrections are made in the source conversion tools and published by rebuilding the dataset.