Abstract
We present Spitzer imaging of the metal-deficient (Z ≃ 30% Z ⊙) Local Group dwarf galaxy NGC 6822. On spatial scales of ∼ 130 pc, we study the nature of IR, Hα, H I, and radio continuum emission. Nebular emission strength correlates with IR surface brightness; however, roughly half of the IR emission is associated with diffuse regions not luminous at Hα (as found in previous studies). The global ratio of dust to H I gas in the ISM, while uncertain at the factor of ∼2 level, is ∼25 times lower than the global values derived for spiral galaxies using similar modeling techniques; localized ratios of dust to H I gas are about a factor of 5 higher than the global value in NGC 6822. There are strong variations (factors of ∼10) in the relative ratios of Hα and IR flux throughout the central disk; the low dust content of NGC 6822 is likely responsible for the different Hα/IR ratios compared to those found in more metal-rich environments. The Hα and IR emission is associated with high column density (≳ 10 21 cm-2) neutral gas. Increases in IR surface brightness appear to be affected by both increased radiation field strength and increased local gas density. Individual regions and the galaxy as a whole fall within the observed scatter of recent high-resolution studies of the radio-far-IR correlation in nearby spiral galaxies; this is likely the result of depleted radio and far-IR emission strengths in the ISM of this dwarf galaxy.
Original language | English (US) |
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Pages (from-to) | 1170-1187 |
Number of pages | 18 |
Journal | Astrophysical Journal |
Volume | 652 |
Issue number | 2 I |
DOIs | |
State | Published - Dec 1 2006 |
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
Keywords
- Galaxies: ISM
- Galaxies: dwarf
- Galaxies: individual (NGC 6822)
- Galaxies: irregular
- Infrared: galaxies