sandyyuan/desi-dr1-elg-spectra

DESI DR1 ELG Galaxy Spectra Dataset

This dataset contains 999 Emission Line Galaxy (ELG) spectra from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1, along with associated metadata. This is a curated sample of high-quality galaxy spectra suitable for research and educational purposes in astronomy and cosmology.

Dataset Contents

• metadata.csv - Galaxy properties and catalog information (999 galaxies + header)
• spectrum_GALAXY_*.json - Individual spectrum files (999 files)
• *.py - Analysis and visualization scripts

Metadata Columns (metadata.csv)

Column	Description
targetid	DESI target identifier
galaxy_type	Galaxy type classification (ELG)
spectype	Spectroscopic type (GALAXY)
ra, dec	Right ascension and declination (degrees)
redshift	Spectroscopic redshift
z_bin	Redshift bin (0.6-0.8, 0.8-1.0)
survey	DESI survey (main)
program	Observing program (dark)
healpix	HEALPix pixel ID
desi_target, bgs_target, mws_target, scnd_target	DESI targeting bitmasks

Spectrum File Format

Each spectrum_GALAXY_*.json file contains:

{
  "metadata": {
    "sparcl_id": "UUID",
    "object_type": "GALAXY",
    "redshift": 0.6004,
    "redshift_err": 7.4e-05,
    "ra": 126.957,
    "dec": 3.269,
    "survey": "main",
    "data_release": "DESI-DR1",
    "targetid": 39636661465776861
  },
  "data": {
    "wavelength": [3600.0, 3600.8, ...],  // 7781 points, 3600-9824 Å
    "flux": [...],                        // Observed flux (10⁻¹⁷ erg/s/cm²/Å)
    "model": [...],                       // Best-fit model
    "inverse_variance": [...]             // 1/σ² for flux uncertainties
  }
}

Quick Start

Load metadata

import pandas as pd
metadata = pd.read_csv('metadata.csv')
print(f"Dataset contains {len(metadata)} ELG galaxies")
print(f"Redshift range: {metadata['redshift'].min():.3f} - {metadata['redshift'].max():.3f}")

Load a spectrum

import json
import numpy as np

# Load spectrum file
with open('spectrum_GALAXY_0.6004_7006c68c_20250811_152534.json', 'r') as f:
    spectrum = json.load(f)

# Extract data
wavelength = np.array(spectrum['data']['wavelength'])
flux = np.array(spectrum['data']['flux'])
model = np.array(spectrum['data']['model'])
redshift = spectrum['metadata']['redshift']

print(f"Galaxy at z={redshift:.4f}")
print(f"Spectrum covers {wavelength[0]:.0f}-{wavelength[-1]:.0f} Å")

Plot a spectrum

import matplotlib.pyplot as plt

plt.figure(figsize=(12, 6))
plt.plot(wavelength, flux, 'k-', alpha=0.7, label='Observed')
plt.plot(wavelength, model, 'r-', label='Model')
plt.xlabel('Wavelength (Å)')
plt.ylabel('Flux (10⁻¹⁷ erg/s/cm²/Å)')
plt.title(f'DESI ELG Spectrum (z={redshift:.4f})')
plt.legend()
plt.grid(True, alpha=0.3)
plt.show()

Analysis Scripts

• plot_desi_spectra.py - Create multi-panel spectrum plots and redshift distributions
• sample_elg_galaxies.py - Original sampling script for ELG selection
• spectrum_downloader.py - Script used to download spectra from DESI archives

Dataset Statistics

• Total galaxies: 999
• Redshift range: 0.600 - 0.948
• Spectral coverage: 3600 - 9824 Å (7781 wavelength points)
• Galaxy type: Emission Line Galaxies (ELGs)
• Survey: DESI Main Survey (dark time program)