Ultrahigh-resolution microwave sky simulations

This repository contains the methods to generate and analyze ultrahigh-resolution (0.04 arcminute) microwave simulations on a patch of the sky.

These simulations are used in MacInnis, Ange, Sehgal, Kable, and Blackstad (2026); if you use this code (or any of the public products that it has generated), please cite that work and the lower-resolution counterpart on which the simulations you generate are based. By default, our simulations are based on the publicly available full-sky maps and catalogs used in Sehgal et al. (2010) (which we will refer to as "S10").

The hdsims code we provide here can be used to produce:

• Simulations of the thermal and kinetic SZ effects (tSZ and kSZ, respectively), the cosmic infrared background (CIB), radio galaxies, the lensing convergence field, and the lensed and unlensed CMB for both temperature and polarization
• Catalogs of the SZ clusters and point sources (CIB and radio) contained in the simulations
• Accurate power spectra of the simulations, corrected for effects such as the incomplete sky coverage or an instrumental beam.

We also provide examples that can reproduce the HD simulations that we have released and Figures 3, 4, and 5 of MacInnis et. al. (2026).

Main task: generate 100 square degree ultrahigh-resolution microwave sky simulations and take their power spectra.

• To do this, run run_hdsims.ipynb. For an example of this done on the patch of sky used in MacInnis et. al. (2026), run the examples/reproduce_10x10.ipynb notebook (see the "Examples" section below for further details). These notebooks will provide instructions to:
  • Download the lower-resolution S10 simulations;
  • Make a 100 square degree high-resolution counterpart from that;
  • Take the power spectra of the high-resolution simulations;
  • Make and save the resulting plots.

Helpful quick-start example: generate 4 square degree versions of the ultrahigh-resolution microwave sky simulations, with the option to skip computationally-intensive steps.

• To do this, run the examples/example_2x2.ipynb notebook (see the "Examples" section below for further details). This notebook will:
  • Use precomputed products by default (or not)
  • Explain tools, extra features, and options of the hdsims package.

To install the hdsims package, navigate to the directory where you would like to place this repository. Then clone and install it via pip:

git clone https://github.com/CMB-HD/hdsims.git
cd hdsims
pip install . --user

To use the hdsims code, you will need to install Python 3 and several Python packages. We make use of Python 3.11.6 and:

• numpy 1.26.0
• scipy 1.11.3
• pandas 2.1.3
• matplotlib 3.8.1
• pixell 0.23.14
• pspy 1.7.5
• healpy 1.17.1
• camb 1.5.4

To generate new simulations, you will need the full-sky maps and catalogs used in Sehgal et al. (2010), which can be downloaded from LAMBDA. We provide a command-line script, download_all_S10sims_data.sh, that will download the necessary files. From the hdsims directory (i.e., the directory where this readme file is located), run the command

bash download_all_S10sims_data.sh /path/to/myS10sims

where /path/to/myS10sims is the path to the directory where you would like to save the S10 files.

Important notes about the S10 simulations:

• Running this command will download the necessary data for all foregrounds and at all frequencies, which is nearly 130 GB of data.
• These files were last modified in 2009: if you are on a cluster and place the files in a "scratch" directory, they may be automatically deleted (depending on the policies on the cluster you're using).
• The full-sky S10 kSZ and lensing convergence sims have a discontinuity along dec. = $0^\circ$ and right ascension = $0^\circ$ and $90^\circ$ ; we recommend that you avoid these regions if you generate new simulations.

We provide a command-line script to download the HD simulations we provide on LAMBDA for a $10^\circ \times 10^\circ$ patch of sky. If you would like to download these simulations, from the hdsims directory (i.e., the directory where this readme file is located), run the command

bash download_all_HDsims_data.sh /path/to/myHDsims

where /path/to/myHDsims is the path to the directory where you would like to save the simulations. Note that we provide separate scripts in the examples/ directory which download only a subset of these files needed to run the example notebooks; see the "Examples" section below for more details.

The HDSims class in the hdsims module (i.e., hdsims/hdsims.py) can be used to generate a new set of simulations, take their power spectra, and plot the results. This can all be done with the generate_hd_sims_and_calculate_powerspectra method of HDSims. We provide a more detailed example (see the "Examples" section below) of how to use the code, but there are only two main steps: (1) initialize the HDSims class, and (2) call the generate_hd_sims_and_calculate_powerspectra method. This is shown in the python snippet below:

from hdsims import hdsims
hd_sims_dir = '/path/to/myHDsims'
lowres_sims_dir = '/path/to/myS10Sims'
simlib = hdsims.HDSims(hd_sims_dir, lowres_sims_dir=lowres_sims_dir)
simlib.generate_hd_sims_and_calculate_powerspectra()

By default, this will generate a set of 0.04 arcminute simulated maps for a $10^\circ \times 10^\circ$ patch of sky centered at R.A. = $6^\circ$, dec. = $6^\circ$ and take their power spectra.

If you download the HD sims we provide on LAMBDA, then you can pass the same hd_sims_dir that you used when downloading the sims. In this case, it would not be necessary to download the S10 sims, and you could set lowres_sims_dir=None in the snippet above.

We provide two examples in the examples directory:

1. examples/example_2x2.ipynb: This is a general example of how to use hdsims to generate a set of simulations on a given patch of sky and take their power spectra. In this example we generate 90 GHz maps for a $2^\circ \times 2^\circ$ patch of sky.
2. examples/reproduce_10x10.ipynb: An example to either reproduce all of the public simulation products provided on LAMBDA and used in MacInnis et. al. (2026) for a $10^\circ \times 10^\circ$ patch of sky, or to only reproduce the plots in that work without needing to generate any simulations.