astro-legacy-archive/guzman-45mhz

Guzmán 45 MHz All-Sky Map

Guzmán et al. combined the Maipú 45 MHz southern survey with the MU radar 46.5 MHz northern survey, scaled to 45 MHz, on a common B1950 grid at 5-degree FWHM. CADE rendered that map onto Galactic HEALPix and LAMBDA mirrors it.

The Maipú array covered declinations at and below +19.1 degrees with a 4.6 x 2.4 degree beam in 1982-1994. The MU radar covered +5 to +65 degrees with a 3.6 x 3.6 degree beam in 1985-1989 and 1997-1999. Both were convolved to the composite's 5-degree resolution. LAMBDA's 2.4-4.6 degree range describes component beams, not this served map.

Pixelisation	HEALPix, NSIDE 64, NESTED, Galactic
Coverage	47,275 pixels (96.18%); 1,877 carry -32768.0
Resolution	5 degrees FWHM
Parquet download	283,519 bytes (about 0.3 MB)

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/guzman-45mhz", "MAIPU_MU_1_64", split="train")
row = dataset.select([0]).select_columns(["UNKNOWN1"])[0]
print(row["UNKNOWN1"][0])

27939.984375

from huggingface_hub import hf_hub_download
import json
import pyarrow.parquet as pq
path = hf_hub_download(repo_id="astro-legacy-archive/guzman-45mhz", repo_type="dataset", filename="guzman-45mhz.parquet")
print(json.loads(pq.ParquetFile(path).schema_arrow.metadata[b"healpix_map"])["healpix"]["ordering"])

NESTED

The data example selects the first element of the first source row. The healpix_map document embedded in the Parquet schema self-describes the NSIDE, ordering, row/element pixel rule, field unit, coverage, provenance, and source headers. To form a validity mask, compare flattened UNKNOWN1 elements with the source value in coverage.codes; 47,275 pixels pass and their measured mean is 8,687.175 K. Resolve requested coordinates using the embedded geometry and the documented row/element rule; the Galactic-centre value is 65,776.26 K.

column	type	unit	description
UNKNOWN1	fixed-size list[1024] of float32	K	Distributed, uncorrected 45 MHz brightness temperature; -32768.0 in two polar caps

UNKNOWN1 is a CADE conversion artefact retained for source identity. Values range from 3312.1477 to 69365.617 K, with median 6765.61 K and mean 8687.18 K. The Galactic centre is 65776.26 K, the anticentre 9147.11 K, and the north Galactic pole 5162.87 K. The brightest pixel lies at (l, b) = (2.11, 0.00) and contains 69365.617 K.

The distributed temperatures are the uncorrected survey values. Guzmán's Table 5 terms combine to a net subtraction of about 550 K for the corrected Galactic temperature: CMB 2.7 K + extragalactic 1100 K - zero-level 544 K. Separately, the unapplied EDGES calibration is T_corrected = 1.076 x T - 160 K, with 2-sigma uncertainties of 0.034 on the scale and 78 K on the offset.

LAMBDA states: "They found that the map of Guzmán et al. requires a scale correction of 1.076 ± 0.034 (2σ) and a zero-level correction of -160 ± 78 K (2σ) to best fit the EDGES data. These correction factors have not been applied to the map that is hosted here."

The 1,877 coverage-code values comprise a genuine 1,387-pixel northern hole and a 490-pixel southern hole in the HEALPix rendering lineage. The rendering input was the MPIfR grid, not the CDS file. The authors' published CDS map nevertheless carries data at all 490 southern-cap positions, so the hole is absent from the science product and arises somewhere in that lineage. The source card declares OBJECT = 'FULLSKY' / Sky coverage, either FULLSKY or PARTIAL; measured coverage is 96.18%. No meaning is assigned to that declaration beyond its own words. The pinned LAMBDA snapshot's older header has no unit keyword; unit K comes from the CADE origin header's BUNIT.

In B1950, every northern coded pixel lies within 19.92 degrees of the north celestial pole and every pixel within 19.17 degrees carries the code. The southern coded pixels lie within 11.53 degrees of the south pole, with every pixel inside 11.28 degrees coded. The authors' CDS map has data at all 490 southern positions. Another 47 rendered pixels sit on the ragged inner edge of blank CDS cells.

Considerations for use

• Apply the coverage code, especially around the artificial southern cap.
• Use 5 degrees as the composite resolution, not the input beam sizes.
• These are distributed, uncorrected temperatures: all foreground, zero-level and scale terms listed above remain unapplied.
• Retain the 2-sigma qualifier on both EDGES correction terms.
• The northern survey observed at 46.5 MHz and was scaled to 45 MHz. The northern and southern surveys overlap between declinations +5 and +19.1 degrees.
• NSIDE-64 pixels are about 0.92 degrees across, greatly oversampling the 5-degree resolution, so neighbouring pixels are correlated.

Provenance

• LAMBDA product page
• CADE product page
• Pinned LAMBDA FITS, 204,480 bytes, SHA-256 f1b43adb264bb429b5a5bc3e4337088e158cde322823211c51206c0aef129a81.
• CADE origin, SHA-256 5e13cdfac81b9cb627990acce2524b4e5606c5438a4ba73526332548740f909f when checked 2026-08-29.
• Authors' WCS form, SHA-256 d56ce071105eea08053a3bf5418e7a7e6a9571357049c0ddf3cafebad1db7688.

CADE rendered the MPIfR Survey Sampler grid, not the CDS file. LAMBDA and CADE have numerically identical decoded data arrays; their headers differ. Rebuild with python tools/make_guzman45.py.

The CDS file is a separate 1441 x 721, 0.25-degree plate-carree WCS product used here only as coverage evidence. LAMBDA's frozen 2017 header predates the BUNIT, BMAJ, RESTFREQ, and TELESCOP cards later added by CADE; the build reads and checks the CADE unit.

The authors' WCS map is VizieR catalogue J/A+A/525/A138, DOI 10.26093/cds/vizier.35250138. Its raw int16 blank code is -32768, which corroborates the measured HEALPix sentinel. CADE used the authors' Galactic grid from the MPIfR Survey Sampler, not this CDS copy, and applied the Paradis et al. 2012 Appendix A drizzling method.

No documentation states the HEALPix sentinel value. It was established by measurement: -32768.0 occurs exactly at all 1,877 blank positions, falls outside the valid-value range, and matches the blank code in the authors' CDS product.

The Parquet file contains 48 source rows. Each UNKNOWN1 value is a fixed-size list of 1,024 consecutive pixels. The source identifies its ordering as NESTED; the embedded pixel_rule specifies how row and list position identify a pixel. The -32768.0 source value remains in-band, so a naive mean is wrong; the example filters the value from coverage.codes before calculating statistics.

Licensing and citations

HEASARC states verbatim:

HEASARC materials are all available freely for your use.

This is a free-use statement rather than a named formal licence.

No explicit licence is published by the authors, CADE, or LAMBDA. CADE requests: "We acknowledge the use of data provided by the Centre d'Analyse de Données Etendues (CADE), a service of IRAP-UPS/CNRS (http://cade.irap.omp.eu, Paradis et al., 2012, A&A, 543, A103)."

VizieR states: "The data retrieved with VizieR are free of usage in a scientific context ; however, as it is the usage in scientific publication, the original authors and publication references including the publisher have to be explicitely cited"

That rule governs the CDS product. It does not license the LAMBDA/CADE derivative, whose redistribution rights are not established.

Please cite Guzmán et al. 2011, A&A 525, A138, DOI 10.1051/0004-6361/200913628; Alvarez et al. 1997, A&AS 124, 315-328; Maeda et al. 1999, A&AS 140, 145-154; and Monsalve et al. 2021, ApJ 908, 145.

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.