Bulk cross-match helpers for collecting archival multi-band photometry, redshifts, and spectra from VizieR/CDS catalogs.

Install from GitHub:

python -m pip install "bandwagon @ git+https://github.com/burke86/bandwagon.git"

For local development:

git clone git@github.com:burke86/bandwagon.git
cd bandwagon
python -m pip install -e ".[dev]"

You can also install the pinned runtime list directly:

python -m pip install -r requirements.txt

Run the tests with:

pytest -q

from astropy.coordinates import SkyCoord
import astropy.units as u
from bandwagon import (
    DEFAULT_CATALOGS,
    matches_to_photometry,
    query_archival_spectra,
    query_simbad_redshifts,
    select_best_redshift,
    xmatch_catalogs,
)

coords = SkyCoord(
    ra=[10.0, 11.0] * u.deg,
    dec=[-2.0, -3.0] * u.deg,
    frame="icrs",
)

matches = xmatch_catalogs(coords, source_id=["src-a", "src-b"])
photometry = matches_to_photometry(matches)

redshift_candidates = query_simbad_redshifts(coords, source_id=["src-a", "src-b"])
redshifts = select_best_redshift(redshift_candidates)

spectra = query_archival_spectra(
    coords,
    source_id=["src-a", "src-b"],
    providers=("desi", "sdss"),
)

SIMBAD redshift queries return a separate long-form table with source_id, object_name, redshift, redshift_err, quality, reference, and match_distance_arcsec. They are not folded into the photometry table, so conflicting redshift candidates can be inspected before selecting one.

Spectra queries are opt-in and return metadata/index rows; they do not download spectra by default. Supported providers are desi, sdss, lamost, 6dfgs, and mast. DESI uses SPARCL and requires the optional spectra extra:

python -m pip install -e ".[spectra]"

LAMOST and 6dFGS are metadata-first VizieR XMatch providers. SDSS and MAST use astroquery. Bandwagon does not use pyvo.

The default catalog set is:

Optional catalog aliases are also available:

matches = xmatch_catalogs(
    coords,
    catalogs={
        **DEFAULT_CATALOGS,
        "2mass": "2mass",
        "akari_irc": "akari_irc",
        "akari_fis": "akari_fis",
        "iras_psc": "iras_psc",
    },
    source_id=["src-a", "src-b"],
)
photometry = matches_to_photometry(matches, min_quality=2)

2mass is converted from Vega magnitudes. AKARI and IRAS publish flux densities, so Bandwagon converts Jy to mJy directly. IRAS uncertainty columns are percent flux uncertainties; AKARI uncertainty columns are Jy. Legacy Survey Tractor-style FLUX_*/FLUX_IVAR_* columns are AB nanomaggies, converted with 1 nanomaggy = 0.003631 mJy; non-positive fluxes or inverse variances are dropped. These rows use distinct filter names (g_legacy, r_legacy, z_legacy, W1_legacy, W2_legacy) so they do not overwrite SDSS or AllWISE measurements.

DESI/Legacy Survey aliases are available for VizieR's DR8 north/south photometric redshift tables. The VizieR VII/292 tables themselves are photo-z catalogs; Bandwagon's Legacy photometry normalization is used when a matched table includes the underlying Tractor flux columns.