To date we have performed work on two fronts, each covering a Theme of the MOPPEX project:
THEME 1: An important part of the project is the enhancements of our in-house codes (Theme 1 WP1) which are all publicly available on
https://uclchem.github.io(s’ouvre dans une nouvelle fenêtre). To date we have
(i) augmented our chemical networks with carbon fractionation reactions and studied their effects on the gas of galaxies; (ii) devised methods for exploiting the topology of reaction networks; (iii) devised an open-source publicly available emulator (CHEMULATOR) for dynamical models; (iv) we employed Bayesian inference and neural network statistical emulation to estimate binding energies and probabilities of reactions for surface reactions; (vi) we devised an application of the MOPED (Massive Optimised Parameter Estimation and DATA) compression algorithm to the determination of which molecules on dust grains should be prioritised by future observations with the JWST.
As the new tools became available, we applied them to generate databases of physically and statistically informed quantities that will allow the community to ultimately use molecules observed in galaxies as rigorous tools to derive the necessary information to determine the formation and the evolution of a galaxy.
In particular we (i) used the latest UCLCHEM chemical code coupled with radiative transfer modelling and statistical approaches, to produce a list of molecular species for which the gas history in a galaxy or in a cloud can be ignored, removing a major modelling complexity. We then determine the best of these species to observe when attempting to constrain various physical parameters and created a public web-based tool (
https://hits.strw.leidenuniv.nl/(s’ouvre dans une nouvelle fenêtre)) whereby a user can search the database we created and determine the best observational lines for their purpose; (ii) created a publicly available, open source first version of the code (UCLCHEMCMC) that allows the user, via a web interface (
https://uclchemcmc.strw.leidenuniv.nl/(s’ouvre dans une nouvelle fenêtre)) to estimate the posterior probability distribution of the gas parameters.
THEME 2: the overarching aim of this Theme is to make use of state of the art observational data of two galaxies (used as astrochemical laboratories and bench-marking cases) as bed-tests for the application of the methodologies developed in Theme 1. As part of our effort to establish the physical and chemical characteristics of parsec-scale molecular gas in nearby galaxies we have been heavily involved in the ALMA large program ALCHEMI and we led or significantly contributed to (i) the study of the emission of the C2H molecule in the central zone of NGC 253 and used it to give initial constraints on the cosmic ray ionization in the centre of the galaxy NGC 253; (ii) the study of the emission of the H3O+ and SO emission in NGC 253 which allowed us to firmly constrain the cosmic ray ionization rate; (iii) the study of the emission of HCN and HNC in NGC 253 to trace the sources of heating in this galaxy. The ALCHEMI work above dealt with the starburst galaxy NGC 253. Our second test-bed was the AGN dominated galaxy NGC 1068; for this galaxy (iv) we - for the first time - performed a systematic analysis of the usefulness of specific molecular ratios to "isolate" AGN-dominated galaxies.
These galaxies are very energetic and the molecular gas in them is highgly affected by shocks. In order to locate and characterize the shock components in these two different types of galaxies: (i) we have determined for the first time the shock structure and location of the shocks in the central nucleus of NGC 1068
and (ii) the nucleus of NGC 253.
All the work performed so far and briefly described above has been published in peer-reviewed articles.
