In asgr/ProSpect: Professional Spectral Analysis Package

Starting Note

First get ProSpect:

install.packages('remotes')
library(remotes)
install_github('asgr/ProSpect') #This might take a while since there is a lot of data embedded in the package.
library(ProSpect)

Where relevant I give link you can type into the R console with the package loaded to have a look at something in more detail, these start with a '?'.

Getting Started

New to Synthetic Spectra? Then take a look here: sedfitting.org. There's a bunch of useful stuff there, and a lot of dead links :-(. But it is worth exploring in some detail. In particular for the stellar population models have a look at BASTI, BPASS, Galaxev (which is BC03 to most astronomers), MILES, Pegase, SLUG and Starburst99. For dust stuff have a look at Dale+Helou and Draine+Li, for UV-FIR Da Cunha (which is MagPhys), CIGALE and Grasil. Those are the most popular variants of what they do in their respective fields. Caveats abound about which is better, but these days they are all pretty sophisticated in their own way.

A New ProSpect

ProSpect is a package that aims to help users explore star formation histories (SFH) and spectral energy distributions (SED). Beneath it all it makes use of the BC03 (?BC03) and EMILES (?EMILES) sythetic stellar population libraries. On top of this it uses the Charlot and Fall model for birth cloud and screen dust attenuation (?CF) and re-emits MIR to FIR flux via the incorporation of the most recent Dale dust templates that model the heating of dust by a radiation field and AGN (?Dale). ProSpect can handle general SFHs via arbitrary functional forms (SFHfunc).

Conceptually this probably all sounds a bit similar to MagPhys and Cegale, bar the different dust model (Dale rather than greybody, though take a look at ?greybody) and some additional SSP libraries (?EMILES). To a degree this is true, but the main reason for putting it all together is to allow proper generative creation of SEDs via the alteration of user accessible parameters and arbitrary SFHs. MagPhys and similar codes do not allow easy access to the under-the-hood generative functionality which might allow this. Doing this is with a longer term aim of incorporating ProSpect into ProFit for multiband morphological decomposition of galaxies, revealing their component-wise SFHs. Before the completion of that component of the project ProSpect offers a readily accessible interface to multiband fitting of SED in order to measure (e.g.) stellar and dust masses, and it can also applied to arbitary SFHs computed by other codes, e.g. create a realistic SED for a semi-analytic (SAM) model SFH.

For most uses getting up and running, having a play with the simplest 5 phase burst star formation (massfunc_p5) is probably the best way to start. Have a read of the documentation and Examples in ?SFHfunc. Fitting data is a more complex affair, but users can get a feel for how this works in practice by looking at ?SFHfunc. The basic idea of these likelihood functions is that they allow the user to provide observed Data and can marginalise over various types of SFH and dust models in order to constrain a set of target parameters. It is also a good idea to get acquainted with the main vignettes covering the BC03 and EMILES data compiled into the package (SSPchecks and Comparisons). These give a good idea how to access the data at a low-level, and allows for easy manipulation and potentially user defined functions for processing them.

The 5 phase model (massfunc_b5) covers 4 key phases of star formation and models them as having constant star formation in each of these periods. By default they cover 0 - 100 Myr (burst, generally considered the shortest phase that broad band photometry can be sensitive to); 100 Myr - 1 Gyr (young; dominated by hot young stars and violent phases of stellar evolution); 1 Gyr - 5 Gyr (mid), 5 Gyr - 9 Gyr (old), and 9 Gyr - 13 Gyr (ancient). It is not really possible to break the SFH into any more independent phases than this using broad band photometry alone, but a physically motivated functional model (e.g. an exponentially decling SFR, or constant SFR) can be used using the functional interface in SFHfunc.

For a typical GAMA galaxy using the 21 band photometry from LAMBDAR a full SFH plus dust model fit takes about one minute using the optim function with the Nelder-Mead minimisation algorithm. A full MCMC will typically take about ten times longer, but in cases of a reasonable fit this is probably over-kill since the Laplace Approximation can be used.

Summary of Things Used

Property | ProSpect Type | Relevant Help ----------------- | -------------------- | --------------- SSPs | BC03 or EMILES | ?BC03 and ?EMILES IMF | Chabrier (2003) for both BC03 and EMILES | ?BC03 and ?EMILES Isochrones | Padova (1994) for both BC03 and EMILES | ?BC03 and ?EMILES Stellar Atmospheres | See relevant text in BC03 and EMILES papers | ?BC03 and ?EMILES Dust Attenuation Law | Charlot and Fall (2000) for birth cloud and screen | ?CF Dust Model | Dale et al (2014) | ?Dale

asgr/ProSpect documentation built on Feb. 21, 2025, 1:43 a.m.