History-independent tracers

Context. Molecular line emission is a powerful probe of the physical conditions astrophysical objects but can be complex to model, and it often unclear which transitions would best targets for observers who wish constrain given parameter. Aims. We produce list molecular species gas history ignored, removing major modelling complexity. then determine these observe when attempting various parameters. Methods. use large set chemical models with different histories have abundances at 1 Myr that are insensitive initial conditions. radiative transfer intensity every transition molecules. finally compute mutual information between parameters all ratios in order rank their usefulness determining value Results. find 48 gas, 23 collisional data available. ranked using properties. show an adequate measure how well parameter by recovering known probes demonstrating random forest regression become more accurate predictors high-scoring features included. Therefore, this used select target observations maximize knowledge about those