MIRISim

I plan to generate COSMOS-Web MIRI images using MIRISim. COSMOS-Web will observe in MIRI F770W with about 0.2 deg^2 coverage.

These are my initial notes on how to use MIRISim.

Installation

I installed MIRISim according to these instructions. Note that MIRISim requires anaconda to install.

I download mirisim_install.bash, and modified the MIRISIM_ROOT environment variable to point to the directory I wanted this installed to. Then, I ran this using:

chmod +x mirisim_install.bash
./mirisim_install.bash

Once this finished, it will tell you the setup commands to export the MIRISim variables to your terminal. I added these to my bash_profile as follows:

export MIRISIM_ROOT=/Users/nicoledrakos/Documents/Software/mirisim/mirisim
export PYSYN_CDBS=$MIRISIM_ROOT/cdbs/

Then conda activate mirisim will allow you to use this package.

Running MIRISim

There are extensive notes on how to use MIRISim here. MIRI has imager (IMA), medium-resolution spectrometer (MRS) and low-resolution spectrometer (LRS). I will only be interested in the imager

The general work-flow within MIRISim consists of the following steps:

1. Create (from description or imported .FITS file) an astronomical scene
2. Add in flux from instrument optics, electronics and background
3. Simulate image slicer (for MRS or LRS)
4. Simulate geometric deformations
5. Disperse the image slices (for MRS or LRS)
6. Add in stochastic cosmic ray hits, photon noise and read noise
7. Output simulated observations.

Input Files

There are three possible input files

1. simulation.ini
2. scene.ini
3. simulator.ini (primarily used for testing, not recommended for general users)

You can generate default configuration files that are commented using the following code:

from mirisim import MiriSimulation
MiriSimulation.generate_configfiles()

Simulation input file

The simulation input file includes user definable parameters, including: pointing, whether to use imager/LRS/MRS, Filter or MRS channel to simulate, exposures, integrations and number of frames, detector mode, dither patterns.

Scene input file

This can include background emission, point sources and galaxies

Output

MIRISim will create a new folder in the working directory, based on the date and time the simulation was run, ending in _mirisim

In addition to copies of the input files and a log file, the folder will contain three directories

1. det_images: detector images in FITS cubes, in format to go into JWST pipeline. Each cube corresponds to a single exposure
2. illum_models: intermediate product illumination models
3. SkyCubes: MRS simulations only

Run Through Imager Example

I went through the “Walk through of MIRISim (Imager)”. This showed an example scene, simulation configuration and how to run. This worked as expected!

Next I need to

1. Figure out how to create a scene with one of my galaxy catalogs (I should be able to read the fits file in directly. What format does this need to be in? How do I specify SED?)
2. Figure out settings for the simulation input file (is this in the APT files?)
3. Figure out how to add point sources to scene

---

« Quiescent Galaxies in COSMOS-Web

MIRISim Scene »