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

Dust and associated depletion of heavy elements from the gas phase can modifythe thermal properties of HII regions from the dust-free case, with significantconsequences for the emergent optical spectrum. We present the results oftheoretical calculations illustrating the effects of grains on the spectra ofgiant, extragalactic HII regions, with emphasis on high metallicity systems(i.e. solar and higher Z). Dust provides a simple explanation for theobservational absence of pure Balmer-line spectra that are expected ontheoretical grounds for dust-free, chemically enriched nebulae. Grains may alsoplay a role in enhancements of forbidden-line emission observed in HII regionsin the enriched nuclei of normal galaxies. In most cases, depletion introducesthe strongest perturbations to the optical spectrum. Selective absorption ofthe ionizing continuum as well as heating by grain photoelectrons are importantin some instances, however, and grain heating can be particularly important forenhancing emission in high-ionization lines. Allowing for depletion, thepresence of dust is unlikely to introduce large errors in global metallicityindicators, although uncertainties in depletion factors coupled with thesensitivity of infrared cooling to electron density will make accuratecalibrations difficult at high Z. The present calculations establish furtherthat previous relative abundance analyses that fail to take into account dusteffects in a self-consistent way (grain heating as well as depletion) mayoverestimate temperature gradients in high-Z nebulae, resulting in errors inrelative abundances for different elements.Comment: 21 pages (AASTeX), plus 9 figures (uuencoded, gzipped, tar), to  appear in ApJ, December 199

Consequences of Dust in Metal-rich H II Regions