English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Recent observations indicate that star formation occurs only in the molecularphase of a galaxy's interstellar medium. A realistic treatment of starformation in simulations and analytic models of galaxies therefore requiresthat one determine where the transition from the atomic to molecular gasoccurs. In this paper we compare two methods for making this determination incosmological simulations where the internal structures of molecular clouds areunresolved: a complex time-dependent chemistry network coupled to a radiativetransfer calculation of the dissociating ultraviolet (UV) radiation field, anda simple time-independent analytic approximation. We show that these twomethods produce excellent agreement at all metallicities >~10^-2 of the MilkyWay value across a very wide range of UV fields. At lower metallicities theagreement is worse, likely because time-dependent effects become important;however, there are no observational calibrations of molecular gas content atsuch low metallicities, so it is unclear if either method is accurate. Thecomparison suggests that, in many but not all applications, the analyticapproximation provides a viable and nearly cost-free alternative to fulltime-dependent chemistry and radiative transfer.

A Comparison of Methods for Determining the Molecular Content of Model Galaxies