To jump straight in and try SÍGAME out, download the first release (version 1.0.0) from GitHub here: https://github.com/kpolsen/SIGAME/releases.
Following line emission
Sígame means 'follow me' in Spanish and refers to the fact that we are following line emission in the far-infrared (FIR) through galaxies at high redshift and towards us. But that is only the last part of SÍGAME - first, the method has to complete the following tasks (described in more detail below):
- Extract a galaxy from a cosmological simulation
- Derive local properties within the galaxy which are not tracked by the simulation
- Subgrid the gas according to physically motivated recipes
- Calculate the line emission, using photoionization code cloudy
- Analyse the resulting velocity-cubes of line emission data
With the velocity cubes we essentially model a real observation of a galaxy resolved in space and velocity. The video below, made by team member Jacob Cluff, illustrates the case for [CII] line emission:
Another way to study the line emission, is to analyze its origin in the interstellar medium (ISM). Below is an example of tracing [CII] back to three different ISM phases; giant molecular clouds (GMCs), the diffuse and neutral gas and the diffuse and ionized gas in red, green and blue, respectively:
We can also study the radial profiles in different emission lines, and divide the emission into contributions from different ISM phases. An example is shown below for a z~6 galaxy in [CII], made by Lily Whitler:
And now, some more details on how the method works.
1. Extracting galaxies from cosmological simulations
SÍGAME uses model galaxies from zooms of cosmological hydrodynamical simulations (see Semelin and Combes 2005 for a description of the zoom-in technique). One very common method, that we have also used for the cosmological simulation, is "smoothed particles hydrodynamics" or SPH. With this method, gas is followed in the simulation as interacting point particles with an attached smoothing length that can be used to map the gas. Here is an example of a z=2 galaxy seen face-on:
The code is currently kept on a private repository, but if you want to use SÍGAME for your project or learn more, you are more than welcome to contact me. Also, we hope to make SÍGAME public and available for the astronomy community in the future.
Publications describing SÍGAME
- [CII], [OI], and [OIII] Line Emission from Star-forming Galaxies at z~6 (2017): ApJ 846 2
Olsen, K, Greve, T, Narayanan, D, Thompson, R, Davé, R, Niebla Rios, L, Stawinski, S
- CO in z~2 normal star-forming galaxies (2016): MNRAS 457 3
Olsen, K, Greve, T, Brinch, C, Sommer-Larsen, J, Rasmussen, J, Toft, S, Zirm, A
- [CII] in z~2 normal star-forming galaxies (2015): ApJ 814 76
Olsen, K, Greve, T, Narayanan, D, Thompson, R, Toft, S, Brinch, C