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   Overview <self>
   SÍGAME module <sigame>
   Getting started <getting-started>


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 <https://ui.adsabs.harvard.edu/abs/2021arXiv210202868O/abstract>`_. 
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 https://kpolsen.github.io/SIGAME/index.html 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 <https://ui.adsabs.harvard.edu/abs/2019MNRAS.486.2827D/abstract>`_].


.. image:: moment0_maps.png

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 <https://ui.adsabs.harvard.edu/abs/2021arXiv210202868O/abstract>`_:

.. image:: flow.png

* 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 <https://kpolsen.github.io/SIGAME-docs/getting-started.html>`_, 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. 

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

* `Cloudy v17.2 <https://www.nublado.org/>`_
* `caesar <https://bitbucket.org/rthompson/caesar>`_
* `SKIRT v9 <https://skirt.ugent.be/version9/_version9.html>`_
* `BPASS v2.2.1 <https://bpass.auckland.ac.nz/9.html>`_
* `SWIFTsimIO <https://github.com/SWIFTSIM/swiftsimio>`_

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

Indices and tables
------------------

* :ref:`genindex`
* :ref:`modindex`
* :ref:`search`