juliensimon/fermi-4lac-agn-catalog
Fermi LAT Fourth AGN Catalog (4LAC) Credit: NASA/JPL-Caltech/STScI/CXC/SAO Part of a dataset collection on Hugging Face. Dataset description Active galactic nuclei (AGN) detected by the Fermi Large Area Telescope, the largest gamma-ray AGN catalog with source classifications, spectral parameters, and redshifts. Active galactic nuclei are supermassive black holes at the centers of galaxies that produce powerful jets of relativistic particles. When one of… See the full description on the dataset page: https://huggingface.co/datasets/juliensimon/fermi-4lac-agn-catalog.
Fermi LAT Fourth AGN Catalog (4LAC)
<div align="center"> <img src="banner.jpg" alt="Cassiopeia A supernova remnant in X-ray, optical, and infrared light" width="400"> <p><em>Credit: NASA/JPL-Caltech/STScI/CXC/SAO</em></p> </div>
Part of a [dataset collection](https://huggingface.co/collections/juliensimon/physics-datasets-69c2d4682d37dfdb77447bd7) on Hugging Face.
Dataset description
Active galactic nuclei (AGN) detected by the Fermi Large Area Telescope, the largest gamma-ray AGN catalog with source classifications, spectral parameters, and redshifts.
Active galactic nuclei are supermassive black holes at the centers of galaxies that produce powerful jets of relativistic particles. When one of these jets points toward Earth, the AGN appears as a blazar -- the most common type of gamma-ray source in the sky.
The Fourth LAT AGN Catalog (4LAC) is based on Fermi LAT observations and represents the most comprehensive census of gamma-ray AGN. It includes BL Lac objects, flat-spectrum radio quasars (FSRQs), and other AGN types, with spectral parameters, variability indices, and multiwavelength counterpart associations.
The two dominant blazar subclasses -- BL Lac objects and FSRQs -- represent fundamentally different accretion regimes onto supermassive black holes. FSRQs are high-luminosity sources with strong broad emission lines, radiatively efficient accretion disks, and gamma-ray spectra that tend to be soft due to dominant external Compton scattering. BL Lac objects have weak or absent emission lines, radiatively inefficient accretion flows, and harder gamma-ray spectra produced primarily by synchrotron self-Compton emission within the jet.
The gamma-ray properties in 4LAC, combined with radio, optical, and X-ray data, enable construction of broadband spectral energy distributions (SEDs) spanning over 15 decades in frequency, constraining physical jet models and distinguishing between leptonic and hadronic emission scenarios.
This dataset is suitable for tabular classification tasks.
Schema
Quick stats
- 3,407 active galactic nuclei
- 1,806 sources with measured redshift
- Median redshift: 0.560
Usage
from datasets import load_dataset
ds = load_dataset("juliensimon/fermi-4lac-agn-catalog", split="train")
df = ds.to_pandas()from datasets import load_dataset
ds = load_dataset("juliensimon/fermi-4lac-agn-catalog", split="train")
df = ds.to_pandas()
# Brightest AGN by flux
top = df.nlargest(10, "flux")[["name", "flux", "spectral_index", "redshift"]]
print(top)
# Redshift distribution
import matplotlib.pyplot as plt
df["redshift"].dropna().hist(bins=50)
plt.xlabel("Redshift")
plt.title("4LAC AGN Redshift Distribution")
plt.show()Data source
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermilac.html
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About the author
Created by Julien Simon — AI Operating Partner at Fortino Capital. Part of the Space Datasets collection.
Citation
@dataset{fermi_4lac_agn_catalog,
title = {Fermi LAT Fourth AGN Catalog (4LAC)},
author = {Simon, Julien},
year = {2026},
url = {https://huggingface.co/datasets/juliensimon/fermi-4lac-agn-catalog},
publisher = {Hugging Face},
note = {Derived from NASA HEASARC (High Energy Astrophysics Science Archive Research Center), https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermilac.html}
}