Towards an automatic approach to modelling the circumgalactic medium: new tools for mock making and fitting of metal profiles in large surveys

• Published in: RAS techniques and instruments 2023-01, Vol.2 (1), p.470-491
• Main Authors: Longobardi, Alessia, Fossati, Matteo, Fumagalli, Michele, Agarwal, Bhaskar, Lofthouse, Emma, Galbiati, Marta, Dutta, Rajeshwari, Berg, Trystyn A.M, Welsh, Louise A
• Format: Article
• Language: English
• Subjects: Baryons; Dark matter (Astronomy); Evolution; Galaxies; Machine learning
• ISSN: 2752-8200; 2752-8200
• DOI: 10.1093/rasti/rzad031

We present two new tools for studying and modelling metal absorption lines in the circumgalactic medium. The first tool, dubbed ‘NMF Profile Maker’ (NMF–PM), uses a non-negative matrix factorization (NMF) method and provides a robust means to generate large libraries of realistic metal absorption profiles. The method is trained and tested on 650 unsaturated metal absorbers in the redshift interval z = 0.9–4.2 with column densities in the range of 11.2 ≤ log (N/cm−2) ≤ 16.3, obtained from high-resolution (R > 4000) and high-signal-to-noise ratio (S/N ≥ 10) quasar spectroscopy. To avoid spurious features, we train on infinite S/N Voigt models of the observed line profiles derived using the code ‘Monte-Carlo Absorption Line Fitter’ (MC–ALF), a novel automatic Bayesian fitting code that is the second tool we present in this work. MC–ALF is a Monte-Carlo code based on nested sampling that, without the need for any prior guess or human intervention, can decompose metal lines into individual Voigt components. Both MC–ALF and NMF–PM are made publicly available to allow the community to produce large libraries of synthetic metal profiles and to reconstruct Voigt models of absorption lines in an automatic fashion. Both tools contribute to the scientific effort of simulating and analysing metal absorbers in very large spectroscopic surveys of quasars like the ongoing Dark Energy Spectroscopic Instrument, the 4-m Multi-Object Spectroscopic Telescope, and the WHT Enhanced Area Velocity Explorer surveys.