juliensimon/first-radio-catalog

FIRST Radio Survey Catalog

Credit: NASA/JPL-Caltech

Part of a dataset collection on Hugging Face.

Dataset description

The Faint Images of the Radio Sky at Twenty-cm (FIRST) survey catalog, covering 10,575 square degrees at 1.4 GHz with 5 arcsecond resolution using the NRAO VLA.

The FIRST survey used the VLA in its B-configuration to produce a map of the radio sky at 1.4 GHz with ~5" resolution and a typical rms of 0.15 mJy/beam. The catalog includes source positions, peak and integrated flux densities, and fitted source sizes.

The FIRST survey was designed as a radio counterpart to the Palomar Observatory Sky Survey, targeting the north and south Galactic caps where optical and infrared surveys provide the richest multi-wavelength context. Its combination of sub-arcsecond positional accuracy and milliJansky sensitivity makes it ideally suited for identifying the radio counterparts of optically selected quasars, galaxies, and other extragalactic objects.

Unlike the broader but lower-resolution NVSS, FIRST resolves the internal structure of extended radio sources, revealing jets, lobes, and hotspots in radio galaxies. The survey's 5-arcsecond beam allows morphological classification of sources and reliable separation of core-dominated and lobe-dominated radio AGN.

Schema

Column	Type	Description	Sample	Null %
source_name	object	FIRST source identifier in the format "JHHMMSS.s+DDMMSS" derived from J2000 position	J030004.5+000946	0.0%
ra_deg	float64	ICRS J2000.0 right ascension in degrees (0-360); positional accuracy ~0.5 arcsec	45.01904166666666	0.0%
dec_deg	float64	ICRS J2000.0 declination in degrees; survey covers ~-10 to +62 deg	0.1630138888888888	0.0%
peak_flux_mjy	float64	Peak surface brightness at 1.4 GHz in mJy/beam; detection threshold ~0.75 mJy/beam	1.04	0.0%
integrated_flux_mjy	float64	Total integrated flux density from Gaussian fit in mJy; use for luminosity calculations	0.97	0.0%
rms_mjy	float64	Local rms noise at source position in mJy/beam; typically ~0.15 mJy/beam	0.104	0.0%
major_axis_arcsec	float64	Fitted (convolved) major-axis FWHM in arcsec; includes 5-arcsec beam	0.39	0.0%
minor_axis_arcsec	float64	Fitted (convolved) minor-axis FWHM in arcsec	0.0	0.0%
position_angle_deg	float64	Fitted position angle of major axis in degrees east from north (0-180)	119.1	0.0%
deconv_major_arcsec	float64	Deconvolved major axis in arcsec; 0 for unresolved point sources	6.17	0.0%
deconv_minor_arcsec	float64	Deconvolved minor axis in arcsec; 0 for unresolved sources	5.28	0.0%
deconv_pa_deg	float64	Deconvolved position angle in degrees; meaningful only when deconv_major_arcsec > 0	169.1	0.0%
is_resolved	bool	Derived: True if deconv_major_arcsec > 0 (source resolved above 5-arcsec beam)	True	0.0%

Quick stats

• 946,432 radio sources at 1.4 GHz
• 946,432 resolved sources (100.0% of catalog)
• Median peak flux: 2.09 mJy/beam
• Sky coverage: 10,575 square degrees (north + south Galactic caps)
• Angular resolution: 5 arcsec (VLA B-configuration)

Usage

from datasets import load_dataset

ds = load_dataset("juliensimon/first-radio-catalog", split="train")
df = ds.to_pandas()

# Flux distribution (log scale — most sources are faint)
import matplotlib.pyplot as plt

fig, axes = plt.subplots(1, 2, figsize=(14, 5))

df["peak_flux_mjy"].clip(upper=100).hist(bins=200, log=True, ax=axes[0])
axes[0].set_xlabel("Peak flux (mJy/beam)")
axes[0].set_ylabel("Count")
axes[0].set_title("FIRST Source Flux Distribution")

# Sky coverage map
axes[1].scatter(df["ra_deg"], df["dec_deg"], s=0.01, alpha=0.1)
axes[1].set_xlabel("RA (deg)")
axes[1].set_ylabel("Dec (deg)")
axes[1].set_title("FIRST Survey Sky Coverage")
plt.tight_layout()
plt.show()

# Resolved vs unresolved statistics
print(f"Resolved:   {df['is_resolved'].sum():,}")
print(f"Unresolved: {(~df['is_resolved']).sum():,}")

Data source

https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=VIII/92

Citation

@dataset{first_radio_catalog,
  title = {FIRST Radio Survey Catalog},
  author = {juliensimon},
  year = {2026},
  url = {https://huggingface.co/datasets/juliensimon/first-radio-catalog},
  publisher = {Hugging Face}
}

License

VizieR Scientific-Use Terms