RoSE-Sim: Roman Semi-resolved Galaxy Simulator

RoSE-Sim is a Python package designed for creating image simulations of semi-resolved dwarf galaxies for the Nancy Grace Roman Space Telescope.

Installation

1. Install the Package

You can install Rosesim locally by cloning the repository and running:

git clone git@github.com:AstroJacobLi/Rosesim.git
cd Rosesim
pip install -e .

2. Set Up Environment Variables

Rosesim requires a dedicated data directory to store large files (e.g., isochrones, sky models).

1. Create a directory for the data (e.g., /scratch/gpfs/user/Rosesim_Data).

2. Set the ROSESIM_DATA_PATH environment variable pointing to this directory. Add the following line to your shell configuration file (e.g., ~/.bashrc or ~/.zshrc):

   export ROSESIM_DATA_PATH="/path/to/your/data/directory"

3. Reload your shell configuration:

   source ~/.bashrc

3. Download Required Data

Once the package is installed and the environment variable is set, you can easily download the necessary data files using the built-in fetch function:

import rosesim
rosesim.fetch_data()

This command downloads the required isochrones and sky models to your ROSESIM_DATA_PATH.

Data Description

Stellar Population Synthesis Models

Rosesim uses PARSEC isochrones for stellar population synthesis.

• Isochrones: Pre-packaged for Roman filters. Note that Roman isochrones are provided in Vega magnitudes.
• Conversion: Zeropoint offsets to convert to AB magnitudes are available in rosesim.Roman_zp_AB_Vega_mist.
• AGB Stars: Special attention has been given to the resolution of thermal pulse cycles (ninTPC=20 in COLIBRI tracks) to strictly resolve AGB stars (see Lee et al. 2025).

Available Grid: (unfortunately, artpop doesn't support the PARSEC isochrones to be interpolated yet)

• Filters: F062, F087, F106, F129, F146, F158, F184, F213
• Log(Age/yr): [8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.1]
• Metallicity [Fe/H]: [-2.00, -1.75, -1.50, -1.25, -1.00, -0.75, -0.50, -0.25, 0.00, +0.25]

Milky Way Star Model

A Milky Way star catalog is generated using the TRILEGAL model.

• Default Field: RA = 10h, Dec = 2.27 deg
• Depth: Limiting magnitude of 30 mag in the 4th filter.
• Location: Stored in ROSESIM_DATA_PATH/TRILEGAL/.

Background Sky Model

To simulate realistic observations, Rosesim includes a background sky model comprising:

1. Background Galaxies: From the JAGUAR mock catalog.
2. Foreground Stars: From the TRILEGAL model.

Caution

JAGUAR fluxes are currently based on JWST filters. A conversion to Roman filters is pending.

Usage

Command Line Interface

Rosesim provides command-line scripts for common simulation tasks. The scripts are located in rosesim/scripts/.

1. Simulate a Sky Model

Generate a full sky model including background galaxies and Milky Way stars:

rosesim_sky \
  --obs_ra=150.1049 \
  --obs_dec=2.2741 \
  --size=5001 \
  --prefix='sky_jaguar_trilegal' \
  --exptime=642 \
  --filters="['F106', 'F129', 'F158']" \
  --seed=42 \
  --include_bkg=True \
  --include_star=True \
  --psf_fov_arcsec=10

To generate an empty sky (for noise-only or background-free simulations):

rosesim_sky \
  --obs_ra=150.1049 \
  --obs_dec=2.2741 \
  --size=5001 \
  --prefix='empty_sky' \
  --exptime=642 \
  --filters="['F106', 'F129', 'F158']" \
  --seed=42 \
  --include_bkg=False \
  --include_star=False \
  --psf_fov_arcsec=10

Check this notebook if you wanna make your own sky model.

2. Simulate a Single Dwarf Galaxy

Inject a specific dwarf galaxy into a simulation:

rosesim_gal \
  --obs_ra=150.1049 \
  --obs_dec=2.2741 \
  --distance=5 \
  --age=1.0 \
  --log_m_star=4 \
  --exptime=642 \
  --sky_model=DATA_PATH + "/sky_jaguar_trilegal/"

A full list of options for simulating the dwarf galaxy is as follows:

simulate_galaxy(
    obs_ra=150.1049,
    obs_dec=2.2741,
    log_m_star=6,
    distance=30,
    age=5,
    feh=-1.5,
    abs_mag_lim=-1,
    filters=["F129", "F158", "F106"],
    exptime=642,
    n=0.8,
    theta=100,
    ellip=0.3,
    sky_model=DATA_PATH + "sky_jaguar_trilegal/",
)

Check this notebook if you wanna tune your dwarf galaxy's properties, such as size, age, metallicity, etc.

Python API

You can also use the Python API to inspect or manipulate data.

Example: inspect the sky model

import rosesim

# Read the simulated ASDF file
sky_dm = rosesim.read_L3_asdf('./F158_642s.asdf')

# Convert to FITS for inspection (e.g., with DS9)
rosesim.asdf_to_fits(sky_dm, 'F158_642s.fits', subtract_bkg=True)

Requirements

The package relies on the following libraries:

• numpy, matplotlib, astropy, astroquery
• artpop, asdf, astrocut, roman_datamodels
• romanisim (Modified version required: GitHub)

Future Plans

• Add stellar population info to ASDF meta.
• Support more diverse sky background options.
• Support composite stellar populations and user-defined structural parameters.
• Expand documentation and examples.
• Enable photometry on the simulated images.

License

MIT