12 research outputs found
EXTINCTION AND POLYCYCLIC AROMATIC HYDROCARBON INTENSITY VARIATIONS ACROSS THE H II REGION IRAS 12063–6259
The spatial variations in PAH band intensities are normally attributed to the
physical conditions of the emitting PAHs, however in recent years it has been
suggested that such variations are caused mainly by extinction. To resolve this
question, we have obtained near-infrared (NIR), mid-infrared (MIR) and radio
observations of the compact H ii region IRAS 12063-6259. We use these data to
construct multiple independent extinction maps and also to measure the main PAH
features (6.2, 7.7, 8.6 and 11.2 {\mu}m) in the MIR. Three extinction maps are
derived: the first using the NIR hydrogen lines and case B recombination
theory; the second combining the NIR data with radio data; and the third making
use of the Spitzer/IRS MIR observations to measure the 9.8 {\mu}m silicate
absorption feature using the Spoon method and PAHFIT (as the depth of this
feature can be related to overall extinction). The silicate absorption over the
bright, southern component of IRAS 12063-6259 is almost absent while the other
methods find significant extinction. While such breakdowns of the relationship
between the NIR extinction and the 9.8 {\mu}m absorption have been observed in
molecular clouds, they have never been observed for HII regions. We then
compare the PAH intensity variations in the Spitzer/IRS data after dereddening
to those found in the original data. It was found that in most cases, the PAH
band intensity variations persist even after dereddening, implying that
extinction is not the main cause of the PAH band intensity variations.Comment: 16 Pages, 17 Figures, 2 Tables. ApJ Accepte
POLYCYCLIC AROMATIC HYDROCARBON EMISSION IN SPITZER
We present a sample of resolved galactic HII regions and photodissociation
regions (PDRs) observed with the Spitzer infrared spectrograph (IRS) in
spectral mapping mode between the wavelengths of 5--15 m. For each object
we have spectral maps at a spatial resolution of 4" in which we have
measured all of the mid-infrared emission and absorption features. These
include the PAH emission bands, primarily at 6.2, 7.7, 8.6, 11.2 and 12.7
m, as well as the spectral emission lines of neon and sulfur and the
absorption band caused by silicate dust at around 9.8 m. In this work we
describe the data in detail, including the data reduction and measurement
strategies, and subsequently present the PAH emission band intensity
correlations for each of the objects and the sample as a whole. We find that
there are distinct differences between the sources in the sample, with two main
groups, the first comprising the HII regions and the second the reflection
nebulae (RNe). Three sources, the reflection nebula NGC~7023, the Horsehead
nebula PDR (an interface between the HII region IC~434 and the Orion B
molecular cloud) and M 17, resist this categorization, with the Horsehead PDR
points mimicking the RNe and the NGC~7023 fluxes displaying unique bifurcated
appearance in our correlation plots. These discrepancies seem to be due to the
very low radiation field experienced by the Horsehead PDR and the very clean
separation between the PDR environment and a diffuse environment in the
NGC~7023 observations.Comment: 17 pages, 9 figures. ApJ accepte