rema

rema finds galaxy clusters in the DESI Legacy Imaging Surveys (Dey et al. 2019) Data Release 11 (DR11) with a red-sequence matched filter written in JAX. From the DR11 sweeps and randoms, it produces catalogues of clusters and of their member galaxies, with the richness λ, the redshift z_λ and the centre of each cluster, found blindly or measured at given positions.

rema is a redesign of redMaPPer (Rykoff et al. 2014, 2016). It keeps redMaPPer's red-sequence model, matched-filter richness λ, z_λ, centring, percolation and redshift scans at given positions, and adds the velocity clipping of Clerc et al. (2016). The code is vectorised JAX: it runs on CPU or GPU, λ has exact implicit derivatives, and the package installs with pip, without a compiler, Spark, Java, GSL, esutil or healsparse.

Versions 0.x are early public releases: the interface may still change before 1.0. rema implements the ingestion of the DR11 sweeps, footprint and depth maps from the randoms, the DR11 griz red-sequence calibration (rema calibrate), zred, backgrounds, richness, z_λ, centring on the brightest cluster galaxy (BCG) or with wcen, blind mode, scan mode, spectroscopic post-processing, and SLURM drivers for high-performance computing (HPC) centres. Cluster finding from the DR11 photometric redshifts (photo-z), whatever the galaxies' colours, is experimental: a photo-z filter in blind and scan mode (--set model.filter=photoz), and rema pscd (Photo-z Space Cluster Detection, PSCD), an implementation of the Adaptive Matched Identifier of Clustered Objects (AMICO) matched filter (Bellagamba et al. 2018; photo-z finders page).

The documentation covers the installation (including the notebook platform of the IN2P3 computing centre, CC-IN2P3), a tour on mock data, DR11 end to end, HPC production, the DR11 catalogue and its validation, the reference, the API and the DR11 notebooks. The design page holds the design and validation notes.

The DR11 south catalogue

We ran the blind mode of rema 0.2.0 over Legacy Surveys DR11 south, on 18 500 deg² with E(B−V) < 0.2 and Galactic latitude |b| ≥ 15°. It found 3 481 608 clusters with λ ≥ 3 (145 133 with λ ≥ 20) and 87.7 M members. The catalogue is on the CC-IN2P3 data system in /sps/lsst/datasets/desi/legacysurveys/dr11/south/rema/rema_dr11_v0.2.0/. Its z_λ scatter against spectroscopic redshifts is 0.0067 (1+z) below z = 0.6, and it recovers 93–95% of the Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT) clusters in its footprint. The results page compares it with the redMaPPer, eROMaPPer, Sunyaev–Zel'dovich (SZ) and X-ray catalogues in 30 figures.

With rema scan-positions, we measured λ, z_λ, the optical centre and the spectroscopic redshift at the 1.64 M clusters of ACT DR5/DR6, SPT-SZ, Planck PSZ2, MCXC, eRASS1, SDSS and DES redMaPPer and Wen & Han (2024). The products are in /sps/lsst/datasets/desi/legacysurveys/dr11/south/rema/rema_dr11_v0.2.0_scan_public/ (public catalogues page).

Installation

Maintainer setup. On the development laptop, use the shared dev environment defined in ~/software/dev_env (conda activate dev); this package is already installed there in editable mode. Do not create a separate environment for it: add missing dependencies to ~/software/dev_env and rebuild.

rema-jax needs Python ≥ 3.11:

pip install rema-jax                # CPU
pip install "rema-jax[cuda]"        # NVIDIA GPU, CUDA 12 JAX wheels ([cuda13] for CUDA 13)

The package is imported as rema and installs the rema command. With the CUDA wheels installed, JAX uses the GPU unless JAX_PLATFORMS=cpu is set; JAX_PLATFORMS=cuda requires the GPU.

For development, from a clone:

git clone https://github.com/JohanComparat/rema-jax.git && cd rema-jax
mamba env create -f environment.yml      # Python 3.12, jax[cuda12], optax, ggah_mod
mamba activate rema
pip install -e ".[dev]"
pytest -m "not slow"                       # unit tests; `pytest -m data` needs the local DR11 files

The DR11 pipeline

Run the commands in a working directory; they read the sweeps and the photo-z sweeps from the DR11 layout (.../south/sweep/11.0/ and .../south/sweep/11.0-photo-z/).

export LEGACYSURVEY_DIR=/path/to/legacysurvey   # CC-IN2P3: /sps/lsst/datasets/desi/legacysurveys
D=$LEGACYSURVEY_DIR/dr11/south

# 1. galaxies: cleaned, dereddened griz fluxes, z-band S/N >= 5, Z_SPEC from the photo-z sweeps
rema ingest $D/sweep/11.0/sweep-000m005-005p000.fits $D/sweep/11.0/sweep-000m010-005m005.fits \
     --out galaxies.fits

# 2. footprint: fraction unmasked and depth per HEALPix pixel, from the DR11 randoms
rema maps $D/randoms/randoms-south-1-0.fits --box 0 5 -10 0 --out footprint.fits

# 3. calibration on DR11 griz (spectroscopic seeds from Z_SPEC; red sequence, background,
#    zred and z_lambda corrections), with diagnostic plots
rema calibrate --galaxies galaxies.fits --footprint footprint.fits --out calib.fits --plots calib_plots
#    (or start from an existing redMaPPer calibration:
#     rema calib-import legacy_dr10_south_v0.3_grz_z_cal_iter1_pars.fit --out calib.fits
#     rema background --galaxies galaxies.fits --calib calib.fits --footprint footprint.fits --out calib.fits)

# 4a. scan mode at given positions (redMaPPer zscan), with spectroscopic post-processing
rema scan --galaxies galaxies.fits --calib calib.fits --footprint footprint.fits \
     --positions act_dr5.fits --ra-col ra --dec-col dec --id-col name --specpost --out scan.fits

# 4b. blind cluster finding (keep clusters centred in the own box); with --checkpoint an
#     interrupted run resumes after its last completed stage
rema blind --galaxies galaxies.fits --calib calib.fits --footprint footprint.fits \
     --own 0 5 -10 0 --checkpoint blind_ckpt --specpost --out clusters.fits

# 4b'. a table of positions anywhere in DR11 south (ingests what it needs): input + results
rema scan-positions targets.csv --out targets_rema.fits

# 4c. the same from the photo-z (any colour), and the AMICO-like PSCD
rema blind ... --set @scripts/photoz/photoz_dr11.yaml --set @scripts/photoz/pz_filter.yaml --out pz.fits
rema pscd --galaxies galaxies.fits --calib calib.fits --footprint footprint.fits \
     --own 0 5 -10 0 --set @scripts/photoz/photoz_dr11.yaml --out pscd.fits

The outputs are FITS files with CLUSTERS and MEMBERS header-data units (HDUs), plus the configuration (CONFIG). Column names follow redMaPPer (LAMBDA, Z_LAMBDA, SCALEVAL, MASKFRAC, ...); the spectroscopic post-processing adds SPEC_Z_BOOT, VDISP, BEST_Z and others. All settings live in a YAML configuration (rema.config.RemaConfig); write the defaults with python -c "from rema.config import RemaConfig; print(RemaConfig().to_yaml())".

Catalogue, notebooks and runs at CC-IN2P3

• Catalogue: /sps/lsst/datasets/desi/legacysurveys/dr11/south/rema/ holds the combined catalogue rema_dr11_v0.2.0/, the two parts of the run with their calibration and logs, and the external catalogues of the results page, as described on the CC-IN2P3 page.
• Notebooks: the DR11 notebooks run on the Jupyter platform https://notebook.cc.in2p3.fr with a rema kernel registered once from an environment on /sps (see the notebooks at CC-IN2P3).
• Running the pipeline again: the driver scripts/slurm/rema_dr11_blind.sh (prepare, run, status, clean) runs with the settings in scripts/slurm/ccin2p3.env. The commands are on the CC-IN2P3 page, and the HPC page describes the driver.

Credits and licence

The algorithms, scan mode (redMaPPer's zscan) included, follow redMaPPer (Rykoff et al. 2014, ApJ 785, 104; Rykoff et al. 2016, ApJS 224, 1), and the spectroscopic post-processing follows Clerc et al. (2016, MNRAS 463, 4490). Distances come from ggah_mod. python -m rema.data.build builds the m*(z) and colour tables in rema/data from redMaPPer's m*(z), the Bruzual & Charlot (2003) simple stellar population (SSP) grid distributed with EzGal (Mancone & Gonzalez 2012) and the speclite filter curves; see rema/data/README.md. The package is distributed under the MIT licence.