astro-legacy-archive/wmap-single-year-maps

WMAP DR5 Single-Year I/Q/U Maps

The preview renders the canonical year-1 K1 TEMPERATURE field in its source NESTED order, using a Galactic Mollweide projection and a symmetric 99.5th percentile colour range.

This dataset contains the complete full-resolution single-year I/Q/U release served by LAMBDA: ten WMAP differencing assemblies for each of nine observing years. These are year-specific, per-assembly measurements. They are distinct from wmap-band-maps-9yr, whose five maps coadd all nine years and combine the assemblies within each frequency band.

The source release contains 90 FITS files and 180 bintable configurations. Every file contains a Stokes Maps table and a separate Weight Arrays table. The current year-2 K1 file is LAMBDA's corrected live object; the other 89 files come from the official bulk tarball.

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/wmap-single-year-maps", "wmap_iqumap_r9_yr1_K1_v5__Stokes Maps", split="train")
row = dataset.select([0]).select_columns(["TEMPERATURE"])[0]
print(row["TEMPERATURE"])

148.0064697265625

from huggingface_hub import hf_hub_download
import json
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/wmap-single-year-maps", "wmap_iqumap_r9_yr1_K1_v5-hdu-1.parquet", repo_type="dataset")
print(json.loads(pq.ParquetFile(path).schema_arrow.metadata[b"healpix_map"])["healpix"]["ordering"])

NESTED

The examples use the first-year K1 Stokes config. Select a year, differencing assembly, and source HDU through its filename-stem config. The embedded healpix_map document supplies geometry, units, coverage, source headers, physics, and provenance without loading a complete map.

Dataset structure

Every table has 3,145,728 scalar rows at HEALPix NSIDE 512 in NESTED ordering and Galactic coordinates. Row i is source pixel i.

source table	verbatim columns	storage and source units
Stokes Maps	TEMPERATURE, Q_POLARISATION, U_POLARISATION, N_OBS	float32; Stokes fields mK,thermodynamic, N_OBS counts
Weight Arrays	N_OBS, QQ, QU, UU	float32; repeated N_OBS has no TUNIT, matrix fields counts

Within each file that has both tables, the two N_OBS arrays are bit-identical. QQ, QU, and UU are the source symmetric polarisation-weight matrix elements. The maps contain no nulls or source blank codes, so coverage.codes is empty.

The maps use the COSMO/HEALPix convention for Q and U. LAMBDA's governing convention page states that a missing POLCCONV keyword means COSMO; these source headers omit that keyword. Stokes I zero levels in the individual-year maps are not set and are not meaningful. LAMBDA states that the nine-year Stokes maps were made by an N_OBS-weighted pixel mean of the nine single-year maps; the nine-year Stokes I maps additionally received a zero-level setting. The combined archive holding also coadds Q1/Q2, V1/V2, and W1–W4 into frequency-band maps. None of those operations is applied here.

Provenance and citations

• Single-year I/Q/U download table
• WMAP sky-map description
• WMAP DR5 overview

The official tarball, delivered 2012-07-28, is 7.61 GiB and has SHA-256 d2575aa9ae0f59c51290be6afea4298d35e0b242b379c9bf57768e0f71a96e0c. Its year-2 K1 member is truncated at 50,339,520 bytes and contains only the Stokes table. LAMBDA currently serves a corrected 100,676,160-byte year-2 K1 object, delivered 2013-07-30, containing both tables; its first 50,339,520 bytes are identical to the complete tar member. This dataset uses that corrected object for year-2 K1 and the pinned tar members for the other 89 files.

Each selected bintable reconstructs in source column and row order with identical TFORM, shape, dtype, and value bits; FITS container serialisation is outside that promise. Each Parquet embeds its individual FITS SHA-256, full headers, source URL, retrieval date, and fixed regeneration command.

Cite Bennett et al. (2013), ApJS 208, 20, DOI 10.1088/0067-0049/208/2/20, arXiv:1212.5225. No explicit licence identifier is published. LAMBDA states that its AWS-hosted WMAP data are freely available for use.

Considerations for use

For a pixel in a differencing assembly, LAMBDA gives the map-noise relation

[ \sigma = \frac{\sigma_0}{\sqrt{N_{\rm OBS}}}. ]

The published uncleaned-map values in mK are:

assembly	K1	Ka1	Q1	Q2	V1	V2	W1	W2	W3	W4
Stokes I	1.429	1.466	2.245	2.131	3.314	2.949	5.899	6.562	6.941	6.773
Stokes Q/U	1.435	1.472	2.254	2.140	3.324	2.958	5.912	6.577	6.958	6.795

The live FITS header states that QQ, QU, and UU must be divided by (\sigma_0^2) to convert the source weight arrays to physical weights in mK(^{-2}).

• Do not interpret the single-year Stokes I zero level physically.
• Keep differencing assemblies separate unless an analysis explicitly performs the documented band coaddition.
• Match Stokes Maps and Weight Arrays by source filename and row position.
• Full-resolution pixels oversample the frequency-dependent WMAP beams.

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.