Tracing the [FeII]/[NeII] ratio and its relationship with other ISM indicators within star forming dwarf galaxies: a Spitzer IRS archival study

B. O'Halloran; S. C. Madden; N. P. Abel

doi:10.1086/588515

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arXiv · 0803.3000

Tracing the [FeII]/[NeII] ratio and its relationship with other ISM indicators within star forming dwarf galaxies: a Spitzer IRS archival study

B. O'Halloran·S. C. Madden·N. P. Abel

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Abstract

Archival Spitzer observations of 41 starburst galaxies that span a wide range in metallicity reveal for the first time a correlation between the [FeII]/[NeII] 26.0/12.8 micron ratio and the electron gas density as traced by the 18.7/33.4 micron [SIII] ratio, with the [FeII]/[NeII] ratio decreasing with increasing gas density. The correlations of the [FeII]/[NeII] ratio, the PAH peak to continuum strength & metallicity found in an earlier paper were confirmed for a larger sample. We also find a strong correlation between the gas density and the PAH peak to continuum strength. Using shock and photoionization models, we see the driver of the observed [FeII]/[NeII] ratios is metallicity. The majority of [FeII] emission in low metallicity galaxies may be shock-derived, whilst at high metallicity, the [FeII] emission may be instead dominated by contributions from HII and in particular from dense PDR regions. However, the observed [FeII]/[NeII] ratios may instead be following a metallicity-abundance relationship, with iron being less depleted onto grains in low metallicity galaxies - a result that would have profound implications for the use of iron emission lines as unambiguous tracers of shocks.

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B. O'Halloran, S. C. Madden, N. P. Abel. 2008-03-20. Tracing the [FeII]/[NeII] ratio and its relationship with other ISM indicators within star forming dwarf galaxies: a Spitzer IRS archival study. https://doi.org/10.1086/588515

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