SIGAME code documentation

SÍGAME: An overview

What the code does

SÍGAME is a module written in python that can make synthetic observations of line emission in the far-infrared (FIR) of galaxies at any redshift. This site describes version 3 of the code, as presented in Olsen et al. 2021. Input to the code is: A table of particle data for a galaxy taken from a cosmological simulation snapshot. Output from the code is: A 3D datacube of line flux in spatial coordinates in kpc (x,y,z) as well as moment 0 maps along any of the three axes. By default, SÍGAME is set up to predict the following emission lines [CII]158, [NII] (122 and 205 microns), [OI] (63 microns), [OIII] (88 microns), [CI] (at 609 and 369 microns), CO(1-0), CO(2-1) and CO(3-2).

See also for a more general description.

An example

Below is an example of what SÍGAME can do. A simulated galaxy at z=0 is processed with SÍGAME to produce maps in three different FIR emission lines; the rotational CO(1-0) line, the fine-structure [CII]158 micron and the [OIII]88 micron line. The input galaxy to SÍGAME in this case came from the 25 Mpc/h volume box of the Simba suite of cosmological simulations [Davé et al. 2019].


The 4 steps of SÍGAME

SÍGAME contains 4 basic steps to calculate the line emission from a galaxy, all of which are summarized in the flow diagram below from Olsen et al. 2021:

  • Step 1 - Dust radiative transfer: The local radiation field strength is determined with the radiative transfer code SKIRT, which calculates the local dust-attenuated stellar spectrum. The SWIFTsimIO package is used to map gas properties from the cosmological simulation output to the cell structure from SKIRT.

  • Step 2 - Additional attenuation by gas: The local interstellar radiation field is further attenuated with the use of a set of Cloudy models of different column densities, by matching the Cloudy transmitted spectrum in the OIR-to-FUV to the dust-attenuated spectrum of SKIRT for each gas cell.

  • Step 3 - Optional additional attenuation: To compensate for lack of resolution in typical cosmological simulations used, attenuation can be added on sub-grid scales with a simple function that can be modified by the user. By default, this function adds attenuation for Cloudy grid models with gas density > 100 cm^−3.

  • Step 4 - Deriving line emission: Finally, Line emission and chemical information are derived from an extensive grid of Cloudy 1-zone models, sampled according to the local density PDF to create a library for a range in values covering: gas density, SFR volume density, column density, FUV flux, metallicity and dust-to-metal ratio.

For step 2 and 3, a Cloudy grid of models is needed. With the release versions, come Cloudy grids for use at z=0, already calculated and stored in the necessary format. To set up and re-run these grids (for instance at a different redshift), see Tutorial 3 that comes with the relase versions.


This version of SÍGAME makes use of the following software, publicly available elsewhere:


For questions, contact Karen at: kpolsen at protonmail . com

Indices and tables