An uncertainty principle for star formation -- V. The influence of dust extinction on star formation rate tracer lifetimes and the inferred molecular cloud lifecycle

TL;DR

This study quantifies how dust extinction affects star formation rate tracer lifetimes, revealing that extinction can significantly alter inferred molecular cloud lifecycles, especially at high gas densities.

Contribution

We extend previous models by incorporating dust extinction effects into SFR tracer time-scale calculations using synthetic emission maps from high-resolution simulations.

Findings

Extinction decreases SFR tracer time-scales by factors of 0.04-1.74.

UV filters are more affected by extinction than Hα filters.

Correcting for extinction impacts molecular cloud lifetime estimates at high gas densities.

Abstract

Recent observational studies aiming to quantify the molecular cloud lifecycle require the use of known 'reference time-scales' to turn the relative durations of different phases of the star formation process into absolute time-scales. We previously constrained the characteristic emission time-scales of different star formation rate (SFR) tracers, as a function of the SFR surface density and metallicity. However, we omitted the effects of dust extinction. Here, we extend our suite of SFR tracer emission time-scales by accounting for extinction, using synthetic emission maps of a high-resolution hydrodynamical simulation of an isolated, Milky-Way-like disc galaxy. The stellar feedback included in the simulation is inefficient compared to observations, implying that it represents a limiting case in which the duration of embedded star formation (and the corresponding effect of extinction) is overestimated. Across our experiments, we find that extinction mostly decreases the SFR tracer emission time-scale, changing the time-scales by factors of 0.04-1.74, depending on the gas column density. UV filters are more strongly affected than H$\alpha$ filters. We provide the limiting correction factors as a function of the gas column density and flux sensitivity limit for a wide variety of SFR tracers. Applying these factors to observational characterisations of the molecular cloud lifecycle produces changes that broadly fall within the quoted uncertainties, except at high kpc-scale gas surface densities ($\Sigma_{\rm g}\gtrsim20~{\mathrm{M_{\odot}\,pc^{-2}}}$). Under those conditions, correcting for extinction may decrease the measured molecular cloud lifetimes and feedback time-scales, which further strengthens previous conclusions that molecular clouds live for a dynamical time and are dispersed by early, pre-supernova feedback.