COSMOLOGY THROUGH THE LYMAN-α FOREST
A window into
the intergalactic universe.
Browse PRIYA simulation files and take the raw spectra
directly into your analysis.
THE DATA
Explore the archive
The lya_emulator GitHub repository contains emulator code and selected flux-power and mean-temperature tables. This catalog provides raw spectra, supporting metadata, and linked simulation output files.
Simulation tiers
LF means low fidelity and HF means high fidelity. The standard PRIYA tiers use the following initial particle counts and comoving box sizes:
| Tier / collection | Initial particles | Box side length (comoving) |
|---|---|---|
| Priya LF · Low fidelity | 15363 gas + 15363 dark matter (2 × 15363 total) | 120 Mpc/h |
| Priya HF · High fidelity | 30723 gas + 30723 dark matter (2 × 30723 total) | 120 Mpc/h |
| Priya Paired · LF resolution | 15363 gas + 15363 dark matter (2 × 15363 total per simulation) | 120 Mpc/h |
Box size is the side length of the periodic cube; h is the dimensionless Hubble parameter H₀/(100 km/s/Mpc). The standard LF and HF configurations are described in the PRIYA paper, Section 2 ↗. Paired parameters are recorded in the archive's SimulationICs.json files.
The spectra headers have been checked across all 68 simulations in this archive: LF and Paired spectra consistently record 15363 dark matter particles, HF spectra record 30723, and all record a 120 Mpc/h box. The npart and box fields in 33 inconsistent SimulationICs.json files have been corrected to match. Gas particle counts in snapshot headers can decrease as gas forms stars.
About the spectra
The standard lya_forest_spectra_grid_480.hdf5 file represents one simulation snapshot and contains three 480 × 480 grids of sightlines, one through each of the x, y, and z axes of the simulation box. That is 691,200 spectra per snapshot, sampled at 10 km/s per pixel. The main snapshot sequence is spaced by Δz = 0.2 from z = 5.4 to z = 2.2; some simulations in this archive also include z = 2.0 spectra. Other spectra variants are identified by their filenames and file metadata. See the PRIYA paper ↗ for the generation method.
The Lyman-α spectra in this archive were generated using fake_spectra ↗, a Python package that creates synthetic absorption spectra from cosmological simulations. It can also load saved spectra for analysis, including flux power spectrum calculations. Install it with pip install fake_spectra.
Browse each simulation's original folder structure: metadata sits in the simulation folder, while spectra are under output/SPECTRA_*. Snapshot labels distinguish spectra with the same filename. Priya LF, Priya HF, and Priya Paired are display names for the source collections; download paths retain their original names. No variant is designated as preferred.
The Priya HF simulation with parameters beginning ns0.979Ap1.78e-09 also includes simulation output archives and supporting files in its original locations. The BlackholeDetails* sets are offered as tar archives for whole-folder downloads. Some archives are hundreds of GB, so check sizes before downloading.
| Select | File / snapshot | Product | Redshift range | Size | Access |
|---|
FROM YOUR TERMINAL
Download from the command line
These commands work on macOS, Linux, and other systems with the required command-line tools installed. Use curl or wget for individual files; bulk downloads use Bash, wget, and jq.
No login or API key is required. Open a file above to get its ready-to-run command, or right-click its Download link and copy the URL.
1. Download a single file
Replace the example URL with the copied link. Run either command in your destination directory. Both resume an interrupted download when you run the same command again.
wget --continue 'PASTE_DOWNLOAD_URL_HERE'
# Or, using curl:
curl --fail --location --retry 3 --continue-at - --remote-name 'PASTE_DOWNLOAD_URL_HERE'2. Download a filtered selection
Open a collection and simulation folder. Select its checkbox to include every file in that folder, or select individual files. You can also search and use Select all shown to select every matching file across all pages. Click Download selected manifest, then use priya-manifest.json on the computer where you want to save the data. If downloading on a remote machine, copy the manifest there first, for example:
scp priya-manifest.json USER@SERVER:~/In your destination directory, use Bash, wget and jq to download the selection. If your terminal uses another shell, enter bash first, or save the example as download.sh and run bash download.sh. The manifest preserves source paths so spectra from different snapshots with the same filename stay separate when downloaded.
# Inspect the selection and total size first.
jq '{files: (.files | length), bytes: ([.files[].bytes] | add // 0)}' priya-manifest.json
# Run in Bash. Downloads go into ./priya-data/.
while IFS=$'\t' read -r path url; do
target="priya-data/$path"
mkdir -p -- "$(dirname -- "$target")" || break
wget --continue --tries=3 --output-document="$target" "$url" || break
done < <(jq -r '.files[] | [.path, .download_url] | @tsv' priya-manifest.json)Rerun the loop to resume interrupted files; wget skips files that are already complete. Use a manifest downloaded from this site. The archive is several TB, so select the products you need and inspect the size before starting.
Build a selection entirely from the command line
Fetch the catalog, then select one collection and non-emulator product using jq. Change the two filter values as needed. Run the download loop above with the resulting manifest.
curl --fail --location --output catalog.json \
'https://larc.ucr.edu/priya/releases/20261111-v3/api/catalog.json'
# Priya HF uses the source collection key emu_full_hires.
jq --arg collection 'emu_full_hires' --arg kind 'Raw spectra' \
'{files: [.files[]
| select(.collection == $collection and .kind == $kind)
| .download_url |= (if startswith("/") then "https://larc.ucr.edu" + . else . end)]}' \
catalog.json > priya-manifest.jsonOriginal HDF5 downloads preserve the stored spectra and redshift coverage.
Original download links point to the live archive. Resume against the same source version; if a file has been replaced, remove your partial copy and download it again. File sizes are listed in the manifest; checksums are not currently provided.
ABOUT THE PROJECT
From simulated forests
to cosmological measurements.
PRIYA is a suite of cosmological hydrodynamic simulations designed to study the one-dimensional Lyman-α forest flux power spectrum.
This public catalog describes the files in the current archive at the catalog indexing time. Its coverage and variants can differ from published releases. Redshifts and array dimensions come from the files themselves.
Use the data
Download original HDF5 spectra and their supporting metadata. Original files link to the live archive and support HTTP range requests for resuming transfers.
Files retain their native simulation arrays. Collection JSON files provide additional simulation metadata.
Background & citation
PRIYA: A New Suite of Lyman-alpha Forest Simulations for Cosmology ↗Please cite the PRIYA paper when using these simulations. Display names differ from source collection keys; no preferred variant is designated here.
GET IN TOUCH
Questions or problems?
Website & database
For broken downloads, missing files, or problems using this catalog, contact:
Yanhui Yang
yyang440@ucr.edu
Science questions
For questions about the PRIYA simulations or their scientific use, contact:
Simeon Bird
sbird@ucr.edu