astro-legacy-archive/arcade2-sky-maps

ARCADE 2 Sky Maps

Regenerate the preview from the published Parquet data with python tools/render_hub_preview.py arcade2-sky-maps datasets/arcade2-sky-maps/preview.png.

These twelve maps are the calibrated sky-map measurement release from the July 2006 flight of ARCADE 2. The cryogenic differential radiometers compared the sky with a full-aperture blackbody calibrator. The maps retain absolute sky intensity after removal of the CMB dipole; no other Galactic or cosmological source was removed.

Each config preserves one LAMBDA FITS filename stem. Frequencies range from 3.15 to 89.8 GHz. Multiple configs at nearby nominal frequencies are distinct radiometer channels, not interchangeable renderings. The s filename suffixes remain part of their source identities.

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/arcade2-sky-maps", "arc2_3150_v19", split="train")
row = dataset.select([0]).select_columns(["TEMPERATURE"])[0]
print(row["TEMPERATURE"])

3.0873405933380127

from huggingface_hub import hf_hub_download
import json
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/arcade2-sky-maps", "arc2_3150_v19.parquet", repo_type="dataset")
print(json.loads(pq.ParquetFile(path).schema_arrow.metadata[b"healpix_map"])["healpix"]["ordering"])

NESTED

The example uses one representative channel. Choose another config by its source filename stem. The embedded healpix_map document records geometry, field units, coverage populations, source headers, provenance, and physics. Coverage-sensitive work should use its measured zero populations rather than turning them into nulls; the source values remain in-band.

Dataset structure

Every config contains 3,072 scalar rows, one for each NSIDE-16 NESTED HEALPix pixel in Galactic coordinates.

column	type	source unit	description
TEMPERATURE	float32	K	Absolute thermodynamic sky temperature; CMB dipole removed
N_OBS	float32	counts	Number of 0.5-second integrations in the pixel

TEMPERATURE=0 and N_OBS=0 identify the same measured pixel populations, between 2,840 and 2,865 pixels depending on channel. The source and LAMBDA page do not attach a separate code definition to zero, so the metadata records only the measured values and counts. No config contains NaNs, infinities, or FITS null values. Nonzero N_OBS values are integer-valued despite float32 storage.

The ordinary channels have documented 11.6-degree FWHM beams. LAMBDA documents arc2_29500s_v19 with a 4-degree FWHM beam. The source FREQ cards are retained verbatim: in particular the values in the two highest-frequency files are 22,664 and 24,264 because of their source integer representation. The filename and product documentation independently identify those channels as 88,200 and 89,800 MHz; the structured metadata keeps the two bases distinct.

Provenance and citations

• ARCADE 2 download table
• ARCADE 2 map description

The twelve source files were delivered by LAMBDA on 2011-07-04. Each selected FITS bintable reconstructs in source column and row order with identical TFORM, shape, dtype, and value bits; FITS container serialisation is outside that promise. Source URLs, byte sizes, SHA-256 pins, complete FITS headers, and the fixed regeneration command are embedded in every Parquet file.

Cite Fixsen et al. (2011), ApJ 734, 5, DOI 10.1088/0004-637X/734/1/5; Kogut et al. (2011), ApJ 734, 4, DOI 10.1088/0004-637X/734/1/4; and Singal et al. (2011), ApJ 730, 138, DOI 10.1088/0004-637X/730/2/138.

No explicit licence identifier is published for these files. LAMBDA is a service of HEASARC and the Astrophysics Science Division at NASA/GSFC.

Considerations for use

• The maps cover only the ARCADE flight scan despite using a full-sphere grid.
• Pixel values are thermodynamic kelvin, not antenna temperature.
• Keep the distinct radiometer channels separate, including equal-frequency ordinary and s configurations.
• The several-mK zero-level accuracy and per-map white-noise amplitudes are described in Fixsen et al. and Singal et al.; they are not per-pixel columns.

Licence

HEASARC states verbatim:

HEASARC materials are all available freely for your use.

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

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.