TY - JOUR
T1 - Near-infrared spectroscopy of diffuse galactic radiation with AKARI/IRC
AU - Onaka, Takashi
AU - Mori, Tamami I.
AU - Sakon, Itsuki
AU - Ohsawa, Ryou
AU - Nakamura, Tomohiko
AU - Lee, Ho Gyu
AU - Koch, Ingrid M.
AU - Shimonishi, Takashi
AU - Kaneda, Hidehiro
AU - Okada, Yoko
AU - Tanaka, Masahiro
PY - 2013
Y1 - 2013
N2 - We present the results of near-infrared (NIR: 2.5-5 μm) spectroscopy of diffuse Galactic sources on the Galactic plane obtained with the Infrared Camera (IRC) on board AKARI. The spectral region of 2.5-5 μm is rich in various emission and absorption features. In this report, we focus on the H2O and CO2 ice absorption features at 3.0 and 4.3 μm, respectively, and report a search for features of deuterated polycyclic aromatic hydrocarbons (PAHs) in 4.4-4.6 μm. The column densities of CO2 and H2O ices show a correlation in agreement with that obtained with ISO observations. The correlation nearly crosses the origin, suggesting that H2O and CO2 ices form in tandem for a wide range of physical conditions. The ratio of the ice column densities in AFGL2591 along the slit is relatively constant over an area of 30", also supporting the tandem formation of H2O and CO2 ices. The H2O ice column density shows a weak trend with AV estimated from HI recombination lines, which is in contrast to the clear correlation seen toward quiescent clouds. The weak correlation may be attributed partly to the uncertainty in AV and/or a range of the environmental conditions in the present targets. Only weak excess emission is seen in 4.4-4.6 μm in the spectra of the Orion bar, M17, and a reflection nebula. From these spectra, the ratio of deuterated PAHs to undeuterated PAHs is estimated as 3% at most. This is significantly smaller than the previously reported value and suggests that missing deuterium must reside in large PAHs that do not emit the 3 μm bands, if it is depleted into PAHs.
AB - We present the results of near-infrared (NIR: 2.5-5 μm) spectroscopy of diffuse Galactic sources on the Galactic plane obtained with the Infrared Camera (IRC) on board AKARI. The spectral region of 2.5-5 μm is rich in various emission and absorption features. In this report, we focus on the H2O and CO2 ice absorption features at 3.0 and 4.3 μm, respectively, and report a search for features of deuterated polycyclic aromatic hydrocarbons (PAHs) in 4.4-4.6 μm. The column densities of CO2 and H2O ices show a correlation in agreement with that obtained with ISO observations. The correlation nearly crosses the origin, suggesting that H2O and CO2 ices form in tandem for a wide range of physical conditions. The ratio of the ice column densities in AFGL2591 along the slit is relatively constant over an area of 30", also supporting the tandem formation of H2O and CO2 ices. The H2O ice column density shows a weak trend with AV estimated from HI recombination lines, which is in contrast to the clear correlation seen toward quiescent clouds. The weak correlation may be attributed partly to the uncertainty in AV and/or a range of the environmental conditions in the present targets. Only weak excess emission is seen in 4.4-4.6 μm in the spectra of the Orion bar, M17, and a reflection nebula. From these spectra, the ratio of deuterated PAHs to undeuterated PAHs is estimated as 3% at most. This is significantly smaller than the previously reported value and suggests that missing deuterium must reside in large PAHs that do not emit the 3 μm bands, if it is depleted into PAHs.
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M3 - Conference article
AN - SCOPUS:85019506094
JO - Proceedings of Science
JF - Proceedings of Science
SN - 1824-8039
T2 - Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments, LCDU 2013
Y2 - 18 November 2013 through 22 November 2013
ER -