Milliquas — Million Quasars Catalog v8

Part of the Astronomy Datasets collection on Hugging Face.

The Million Quasars (Milliquas) v8 catalog — 1,021,800 quasars, AGN, and blazars, the most comprehensive compilation of its kind. Includes 860,100 type-I QSOs/AGN with positions, redshifts, optical magnitudes, and radio/X-ray associations.

Dataset description

Milliquas v8 (Flesch 2023) is a compendium of over 1 million quasars and active galactic nuclei drawn from the literature and major surveys (SDSS, 2QZ, 6QZ, LAMOST, etc.). It includes type-I QSOs, AGN, blazars, and type-II objects, each with sky position, redshift, optical magnitudes, and cross-identifications with radio and X-ray surveys. This catalog is widely used for quasar target selection, AGN demographics, and cross-matching with multi-wavelength surveys.

Schema

Column	Type	Description
name	string	Object name/designation
ra_deg	float64	Right ascension J2000 (degrees)
dec_deg	float64	Declination J2000 (degrees)
object_type	string	Classification type (Q = QSO, A = AGN, B = BL Lac, etc.)
redshift	float64	Spectroscopic redshift
r_mag	float64	Red optical magnitude
b_mag	float64	Blue optical magnitude
qso_probability_pct	float64	QSO probability percentage
reference	string	Literature reference code
radio_name	string	Associated radio source name
xray_name	string	Associated X-ray source name
is_qso	bool	True if object type contains "Q"
has_radio	bool	True if radio association exists
has_xray	bool	True if X-ray association exists

Quick stats

• 1,021,800 objects total
• 860,100 QSOs (type contains "Q")
• 1,012,635 with measured redshift
• Redshift range: -0.001 to 7.642 (median 1.585)
• 155,286 with radio associations
• 104,604 with X-ray associations

Usage

from datasets import load_dataset

ds = load_dataset("juliensimon/milliquas", split="train")
df = ds.to_pandas()

# High-redshift quasars (z > 4)
high_z = df[df["redshift"] > 4].sort_values("redshift", ascending=False)
print(f"{len(high_z):,} quasars with z > 4")

# Redshift distribution
import matplotlib.pyplot as plt
df["redshift"].dropna().hist(bins=200, range=(0, 7))
plt.xlabel("Redshift")
plt.ylabel("Count")
plt.title("Milliquas Redshift Distribution")

Data source

Flesch, E.W. (2023), "The Million Quasars (Milliquas) v8 catalogue", arXiv:2308.01505. Accessed via VizieR catalog VII/294, CDS Strasbourg.

Related datasets

• quasar-catalog — SIMBAD Quasar & AGN Catalog
• galaxy-cluster-catalog — Galaxy Cluster Catalog
• gravitational-lenses — Gravitational Lens Catalog

Pipeline

Source code: juliensimon/space-datasets

Support

If you find this dataset useful, please give it a ❤️ on the dataset page and share feedback in the Community tab! Also consider giving a ⭐️ to the space-datasets repo.

Citation

@dataset{milliquas,
  author = {Simon, Julien},
  title = {Milliquas — Million Quasars Catalog v8},
  year = {2026},
  publisher = {Hugging Face},
  url = {https://huggingface.co/datasets/juliensimon/milliquas},
  note = {Based on Milliquas v8 (Flesch 2023, arXiv:2308.01505) via VizieR CDS Strasbourg}
}

License

CC-BY-4.0