Tutorial: Recreating the ACT DR6 Cluster Search Data Products
Here we provide a guide to reproducing the ACT DR6 cluster search data products, as described in the ACT DR6 cluster catalog paper.
Note
This is under construction. It will probably only be completed after a new Nemo release is made together with an updated release of the ACT DR6 cluster search products. So, fully up-to-date documentation might not be found in the Nemo source distribution corresponding to the latest stable release.
Note
The config files and scripts needed for this tutorial can be found in the examples/ACT-DR6-clusters directory of the Nemo source distribution.
Downloading maps and other needed inputs
The first step is to download the co-added ACT+Planck maps used for the ACT DR6 cluster search. These are described in Naess et al. (2025), and available on LAMBDA. In addition to this, we require the beam transform files and some masks. These can be downloaded and extracted by running a script:
sh FETCH_MAPS.sh
Each map is 5 Gb in size, so this may take a while.
Extracting the cluster candidate list
Nemo breaks large maps into tiles, which can be processed
separately in parallel, before combining the output to make
the final catalogs and filtered maps. This requires the
nemo command to run with the -M switch as below:
mpiexec nemo DR6ClusterSearch.yml -M
The Nemo configuration for the ACT DR6 cluster search is
found in DR6ClusterSearch.yml. See Configuration File Parameters
for a description of the available options and parameters.
This particular configuration finds point sources and clusters
in the ACT maps using a multi-pass approach, as described in
Section 2 of the
ACT DR6 cluster catalog paper.
Point sources are subtracted from the maps before performing
the cluster search and affected pixels are flagged.
The file DR6ClusterSearch.pbs contains an example job script
for running Nemo on a compute cluster. The DR6 cluster search
takes 03h40m to complete, running on 144 CPU cores on Lengau at
the CHPC.
After this job is completed, the cluster candidate list,
filtered maps, and various other files will be found under the
DR6ClusterSearch directory. For more information on what
these are, see Output.
Post-processing runs (footprint and flagging adjustments)
Nemo can be run again on existing output without re-running the full map filtering and object detection pipeline, after adjusting some of the options in the configuration file.
To produce information related to completeness for
different footprints that overlap with the cluster search area, run
nemo with the -S switch as below:
nemo DR6ClusterSearch.yml -S
This does not currently benefit from being run in parallel, and
takes 1h12m to complete on one of the Lengau compute nodes at the
CHPC. The file
DR6ClusterSearch-S.pbs contains a job script for running
nemo in this way.
The selFnOptions and selFnFootprints keywords in the
DR6ClusterSearch.yml configuration file control which regions
completeness statistics are calculated for. The information on
mass limits depends upon the assumed scaling relation parameters
set in massOptions (see Configuration File Parameters).
After running nemo with the -S switch,
plots corresponding to Figures 8, 9 and 10 of the
ACT DR6 cluster catalog paper.
will be found
under the DR6ClusterSearch/diagnostics directory.
Post-processing flags can also be adjusted by re-running
nemo after editing the postFlags keyword in the
DR6ClusterSearch.yml configuration file. This allows masks
that are not related to object finding to be changed, such as the
dust mask, and regions flagged around extended objects (e.g. nearby
galaxies) and bright stars.
Estimating cluster masses
To infer cluster masses, a redshift catalog is needed. This is provided
for the ACT DR6 clusters in the file redshifts.fits,
which is included in the ACTDR6ClustersExtras.tar.gz archive downloaded
by the FETCH_MAPS.sh script.
The nemoMass tool can be used to estimate cluster masses:
mpiexec nemoMass DR6ClusterSearch.yml -M
This should take a few minutes to run, and will write a FITS-table
format catalog to DR6ClusterSearch/DR6ClusterSearch_mass.fits.
The inferred masses depend on the assumed scaling relation
parameters, which can be edited in the massOptions section of the
DR6ClusterSearch.yml config file.
Making model cluster signal maps
To be added.
Forced photometry
To be added.
Running source injection simulations
To be added.