{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/pdfchem-a-new-fast-method-to-determine-ism","title":"PDFchem: A new fast method to determine ISM properties and infer environmental parameters using probability distributions","arxiv_id":"2211.12974","date":"2022-11-23","proceeding":null,"authors":["Thomas G. Bisbas","Ewine F. van Dishoeck","Chia-Yu Hu","Andreas Schruba"],"abstract":"Determining the atomic and molecular content of the interstellar medium (ISM) as a function of environmental parameters is of fundamental importance to understand the star-formation process across the epochs. Although there exist various three-dimensional hydro-chemical codes modelling the ISM at different scales and redshifts, they are computationally expensive and inefficient for studies over a large parameter space. Building on our earlier approach, we present PDFchem, a novel algorithm that models the cold ISM at moderate and large scales using functions connecting the quantities of the local ($A_{\\rm V,eff}$) and the observed ($A_{\\rm V,obs}$) visual extinctions, and the local number density, $n_{\\rm H}$, with probability density functions (PDF) of $A_{\\rm V,obs}$ on cloud scales typically tens-to-hundreds of pc as an input. For any given $A_{\\rm V,obs}$-PDF, sampled with thousands of clouds, the algorithm instantly computes the average abundances of the most important species (HI, H$_2$, CII, CI, CO, OH, OH$^+$, H$_2$O$^+$, CH, HCO$^+$) and performs radiative transfer calculations to estimate the average emission of the most commonly observed lines ([CII]~$158\\mu$m, both [CI] fine-structure lines and the first five rotational transitions of $^{12}$CO). We examine two $A_{\\rm V,obs}$-PDFs corresponding to a non star-forming and a star-forming ISM region, under a variety of environmental parameters combinations. These cover FUV intensities in the range of $\\chi/\\chi_0=10^{-1}-10^3$, cosmic-ray ionization rates in the range of $\\zeta_{\\rm CR}=10^{-17}-10^{-13}\\,{\\rm s}^{-1}$ and metallicities in the range of $Z=0.1-2\\,{\\rm Z}_{\\odot}$. PDFchem is fast, easy to use, reproduces the PDR quantities of the time-consuming hydrodynamical models and can be used directly with observed data to understand the evolution of the cold ISM chemistry.","url_abs":"https://arxiv.org/abs/2211.12974v1","url_pdf":"https://arxiv.org/pdf/2211.12974v1.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"pdfchem-a-new-fast-method-to-determine-ism","repo_url":"https://github.com/tbisbas/PDFchem","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":{"status":"ok"}}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":"https://app.syntology.ai/?focus=2211.12974","mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}