OBSERVATIONAL STUDIES ON THE NEAR-INFRARED UNIDENTIFIED EMISSION BANDS IN GALACTIC H II REGIONS

Using a large collection of near-infrared spectra (2.5-5.4 mu m) of Galactic H II regions and H II region-like objects, we perform a systematic investigation of astronomical polycyclic aromatic hydrocarbon (PAH) features. Thirty-six objects were observed using the infrared camera on board the AKARI...

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Bibliographic Details
Published in:The Astrophysical journal 2014-03, Vol.784 (1), p.1-12
Main Authors: Mori, Tamami I, Onaka, Takashi, Sakon, Itsuki, Ishihara, Daisuke, SHIMONISHI, TAKASHI, Ohsawa, Ryou, Bell, Aaron C
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Boundaries
COLOR
Continuums
CORRELATIONS
DISTRIBUTION
DUSTS
EMISSION
Emission analysis
H II regions
INFRARED SPECTRA
Ionization
NEAR INFRARED RADIATION
Onboard
Polyallylamine hydrochloride
POLYCYCLIC AROMATIC HYDROCARBONS
SATELLITES
SIGNAL-TO-NOISE RATIO
Vibration
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Summary:Using a large collection of near-infrared spectra (2.5-5.4 mu m) of Galactic H II regions and H II region-like objects, we perform a systematic investigation of astronomical polycyclic aromatic hydrocarbon (PAH) features. Thirty-six objects were observed using the infrared camera on board the AKARI satellite as a part of a director's time program. In addition to the well known 3.3-3.6 mu m features, most spectra show a relatively weak emission feature at 5.22 mu m with sufficient signal-to-noise ratios, which we identify as the PAH 5.25 mu m band (previously reported). By careful analysis, we find good correlations between the 5.25 mu m band and both the aromatic hydrocarbon feature at 3.3 /rm and the aliphatic hydrocarbon features at around 3.4-3.6 mu m. The present results give us convincing evidence that the astronomical 5.25 mu m band is associated with C-H vibrations, as suggested by previous studies, and show its potential to probe the PAH size distribution. The analysis also shows that the aliphatic-to-aromatic ratio of I3.4-3.6 mu m/I sub(3.3) mu m decreases against the ratio of the 3.7 mu m continuum intensity to the 3.3 mu m band, Icont.3.7 mu m/I 3.3 mu m which is an indicator of the ionization fraction of PAHs. The midinfrared color of I9 mu m/I sub(18) mu m also declines steeply against the ratio of the hydrogen recombination line Br alpha at 4.05 mu m to the 3.3 mu m band, IBr alpha /I3.3 mu m - These facts indicate possible dust processing inside or at the boundary of ionized gas.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/784/1/53