Grids

Introduction

Most of the functionality of synthesizer is reliant on grid files. These are typically precomputed multi-dimensional arrays of spectra (and lines) from Stellar Population Synthesis (SPS) models for a range of ages and metallicities, and potentially other parameters (see below). Grids can also represent the emission from other sources, e.g. active galactic nuclei.

There is a low-resolution test grid available via the synthesizer-download command line tool, but for actual projects you will need to download one or more full production grids from dropbox. See details below on where on your system to download these grids and how to load them.

The Grid Directory

All synthesizer grids should be stored in a separate directory somewhere on your system. For example, we can create a folder:

mkdir /our/synthesizer/data_directory/synthesizer_data/

Within this we will additionally create another directory to hold our grids:

mkdir /our/synthesizer/data_directory/synthesizer_data/grids

If you wish, you can set this grid directory as an environment variable.

Pre-Computed Grids

A goal of synthesizer is to be flexible. With this in mind, we have generated a variety of grids for different SPS models, initial mass functions (IMFs), and photoionisation modelling assumptions.

Grid naming

The naming of grids currently follows this specification:

{sps_model}-{sps_version}-{sps_variant}_{imf_type}-{mass_boundaries}-{slopes}_{photoionisation_code}-{photoionisation_code_version}-{photoionisation_parameters}

e.g.

bpass-2.2.1-bin_chabrier03-0.1,300.0_cloudy-c17.03

specifies that the grid is constructed using v2.2.1 of the Binary Population and Spectral Synthesis (BPASS) SPS model for the binary (bin) variant. This grid assumes the Chabrier (2003) IMF between 0.1 and 300 Msol. Photoionisation modelling is performed using v17.03 of the cloudy photoionisation code assuming our default assumptions.

Initial Mass Function

Grids are constructed using various initial mass functions (IMFs), often depending on the availability in the specific SPS model. In most cases we recommend using the Chabrier (2003) IMF since this is available for most SPS models, allowing a like-for-like comparison. If you’re interested in exploring the systematic impact of changing the IMF, broken power law (bpl) IMFs may be suitable. These are named e.g.

{imf_type}-{mass_boundaries}-{slopes}

e.g. for a Salpeter (1955) IMF (slope=2.35) between 0.1 and 100 Msol we would have

bpl-0.1,100-2.35

A more complex IMF, for example with two power-laws (2.0, 2.35) separated at 1 Msol, would have

bpl-0.1,1.0,100-2.0,2.35

If an IMF you need is missing, please let us know by raising a feature request through an issue.

Photoionisation modelling

All the photoionisation modelling in synthesizer currently uses the cloudy photoionisation code. Our default assumptions are:

• log10(U)=-2

Common variants

• resolution:0.1 outputs the spectra at 10x higher resolution than the cloudy default. Useful for looking at various absorption line indices.

• log10U:X assumes a different ionisation parameter.

Higher-dimensionality grids

Most SPS grids are two-dimensional, with the dimensions being log10(age) and metallicty. However synthesizer can utlilise grids with higher dimensionality e.g. including varying alpha-abundance, or photoionisation parameters (e.g. U).

Grid list

Below is an incomplete list of the pre-computed grids available in the dropbox.

Bruzual & Charlot (2003, BC03)

• Chabrier (2003) IMF

  • bc03_chabrier03-0.1,100

  • bc03_chabrier03-0.1,100_cloudy-c17.03

  • bc03_chabrier03-0.1,100_cloudy-c17.03_resolution:0.1

2016 update of Bruzual & Charlot (2003)

• The BaSel variant

  • Chabrier (2003) IMF

    • bc03-2016-BaSeL_chabrier03-0.1,100

    • bc03-2016-BaSeL_chabrier03-0.1,100_cloudy-c17.03

    • bc03-2016-BaSeL_chabrier03-0.1,100_cloudy-c17.03_resolution:0.1

• The Miles variant

  • Chabrier (2003) IMF

    • bc03-2016-Miles_chabrier03-0.1,100

    • bc03-2016-Miles_chabrier03-0.1,100_cloudy-c17.03

    • bc03-2016-Miles_chabrier03-0.1,100_cloudy-c17.03_resolution:0.1

• The Stelib variant

  • Chabrier (2003) IMF

    • bc03-2016-Stelib_chabrier03-0.1,100

    • bc03-2016-Stelib_chabrier03-0.1,100_cloudy-c17.03

    • bc03-2016-Stelib_chabrier03-0.1,100_cloudy-c17.03_resolution:0.1

Binary Population and Spectral Synthesis (BPASS) v2.2.1

Binary Population and Spectral Synthesis

• Binary variant

  • Broken power-law IMF

    • bpass-2.2.1-bin_bpl-0.1,1.0,100.0-1.3,2.0

    • bpass-2.2.1-bin_bpl-0.1,1.0,100.0-1.3,2.0_cloudy-c17.03

    • bpass-2.2.1-bin_bpl-0.1,1.0,100.0-1.3,2.35

    • bpass-2.2.1-bin_bpl-0.1,1.0,100.0-1.3,2.35_cloudy-c17.03

    • bpass-2.2.1-bin_bpl-0.1,1.0,100.0-1.3,2.7

    • bpass-2.2.1-bin_bpl-0.1,1.0,100.0-1.3,2.7_cloudy-c17.03

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.0

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.0_cloudy-c17.03

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.0_cloudy-c17.03_resolution:0.1

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.35

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.35_cloudy-c17.03

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.35_cloudy-c17.03_resolution:0.1

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.7

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.7_cloudy-c17.03

    • bpass-2.2.1-bin_bpl-0.1,1.0,300.0-1.3,2.7_cloudy-c17.03_resolution:0.1

  • Chabrier (2003) IMF

    • bpass-2.2.1-bin_chabrier03-0.1,100.0

    • bpass-2.2.1-bin_chabrier03-0.1,100.0_cloudy-c17.03

    • bpass-2.2.1-bin_chabrier03-0.1,100.0_cloudy-c17.03_resolution:0.1

    • bpass-2.2.1-bin_chabrier03-0.1,300.0

    • bpass-2.2.1-bin_chabrier03-0.1,300.0_cloudy-c17.03

    • bpass-2.2.1-bin_chabrier03-0.1,300.0_cloudy-c17.03_resolution:0.1

• Single star variant variant

  • Broken power-law IMF

    • bpass-2.2.1-sin_bpl-0.1,1.0,100.0-1.3,2.0

    • bpass-2.2.1-sin_bpl-0.1,1.0,100.0-1.3,2.35

    • pass-2.2.1-sin_bpl-0.1,1.0,100.0-1.3,2.7

    • bpass-2.2.1-sin_bpl-0.1,1.0,300.0-1.3,2.0

    • bpass-2.2.1-sin_bpl-0.1,1.0,300.0-1.3,2.35

    • bpass-2.2.1-sin_bpl-0.1,1.0,300.0-1.3,2.7

  • Chabrier (2003) IMF

    • bpass-2.2.1-sin_chabrier03-0.1,100.0

    • bpass-2.2.1-sin_chabrier03-0.1,300.0

Binary Population and Spectral Synthesis (BPASS) v2.3

Binary Population and Spectral Synthesis

• Binary variant

  • Chabrier (2003) IMF

    • bpass-2.3-bin_chabrier03-0.1,300.0

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha-0.2

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha-0.2_cloudy-c17.03_resolution:0.1

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha0.0

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha0.2

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha0.2_cloudy-c17.03_resolution:0.1

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha0.4

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha0.4_cloudy-c17.03_resolution:0.1

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha0.6

    • bpass-2.3-bin_chabrier03-0.1,300.0_alpha0.6_cloudy-c17.03_resolution:0.1

Flexible Stellar Population Synthesis (FSPS) v3.2

• Broken power-law IMF - Note: several of these are currently missing.

  • fsps-3.2_bpl-0.08,0.5,1,120-1.3,2.3,2.3

  • fsps-3.2_bpl-0.08,0.5,1,120-1.3,2.3,2.3_cloudy-c17.03

  • fsps-3.2_bpl-0.08,0.5,1,120-1.3,2.3,2.8

  • fsps-3.2_bpl-0.08,0.5,1,120-1.3,2.3,2.8_cloudy-c17.03

  • fsps-3.2_bpl-0.08,0.5,1,120-1.3,2.3,2.9

  • fsps-3.2_bpl-0.08,0.5,1,120-1.3,2.3,3.0

• Chabrier (2003) IMF

  • fsps-3.2_chabrier03-0.08,1

  • fsps-3.2_chabrier03-0.08,10

  • fsps-3.2_chabrier03-0.08,100

  • fsps-3.2_chabrier03-0.08,100_cloudy-c17.03

  • fsps-3.2_chabrier03-0.08,120

  • fsps-3.2_chabrier03-0.08,120_cloudy-c17.03

  • fsps-3.2_chabrier03-0.08,120_cloudy-c17.03_resolution:0.1

  • fsps-3.2_chabrier03-0.08,2

  • fsps-3.2_chabrier03-0.08,20

  • fsps-3.2_chabrier03-0.08,5

  • fsps-3.2_chabrier03-0.08,50

  • fsps-3.2_chabrier03-0.08,50_cloudy-c17.03

  • fsps-3.2_chabrier03-0.5,120

  • fsps-3.2_chabrier03-0.5,120_cloudy-c17.03

  • fsps-3.2_chabrier03-1,120

  • fsps-3.2_chabrier03-1,120_cloudy-c17.03

  • fsps-3.2_chabrier03-10,120

  • fsps-3.2_chabrier03-10,120_cloudy-c17.03

  • fsps-3.2_chabrier03-2,120

  • fsps-3.2_chabrier03-2,120_cloudy-c17.03

  • fsps-3.2_chabrier03-20,120

  • fsps-3.2_chabrier03-20,120_cloudy-c17.03

  • fsps-3.2_chabrier03-5,120

  • fsps-3.2_chabrier03-50,120

  • fsps-3.2_chabrier03-50,120_cloudy-c17.03

Maraston models

• Broken power-law IMF

  • maraston-rhb_bpl-0.1,100-2.35

Exploring Grids

Once you’ve downloaded a grid you can get started here:

• Grid example

Creating your own grids

For advanced users, synthesizer contains scripts for creating your own grids from popular SPS codes, and running these through CLOUDY. We provide scripts for doing this in the synthesizer-grids repository. Details are provided here. You will need a working installation of synthesizer for these scripts to work, as well as other dependencies for specific codes (e.g. CLOUDY, python-FSPS). Please reach out to us if you have questions about the pre-computed grids or grid creation.