juliensimon/milliquas

---
license: cc-by-4.0
pretty_name: "Milliquas — Million Quasars Catalog v8"
language:
- en
description: >-
Milliquas v8 — the Million Quasars Catalog containing 1,021,800 quasars, AGN,
and blazars with positions, redshifts, magnitudes, and radio/X-ray associations.
The most comprehensive quasar/AGN compilation available.
size_categories:
- 1M<n<10M
task_categories:
- tabular-classification
- tabular-regression
tags:
- space
- quasars
- agn
- blazars
- active-galaxies
- astronomy
- open-data
- tabular-data
- parquet
configs:
- config_name: default
data_files:
- split: train
path: data/milliquas.parquet
---

# Milliquas — Million Quasars Catalog v8

*Part of the [Astronomy Datasets](https://huggingface.co/collections/juliensimon/astronomy-datasets-69c24caf2f17e36128946743) 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

```python
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](https://vizier.cds.unistra.fr/) catalog VII/294, CDS Strasbourg.

## Related datasets

- [quasar-catalog](https://huggingface.co/datasets/juliensimon/quasar-catalog) — SIMBAD Quasar & AGN Catalog
- [galaxy-cluster-catalog](https://huggingface.co/datasets/juliensimon/galaxy-cluster-catalog) — Galaxy Cluster Catalog
- [gravitational-lenses](https://huggingface.co/datasets/juliensimon/gravitational-lenses) — Gravitational Lens Catalog

## Pipeline

Source code: [juliensimon/space-datasets](https://github.com/juliensimon/space-datasets)

## Support

If you find this dataset useful, please give it a ❤️ on the [dataset page](https://huggingface.co/datasets/juliensimon/milliquas) and share feedback in the Community tab! Also consider giving a ⭐️ to the [space-datasets](https://github.com/juliensimon/space-datasets) repo.

## Citation

```bibtex
@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](https://creativecommons.org/licenses/by/4.0/)