Low-Resolution Spectrum of the Diffuse Galactic Light and 3.3 um PAH emission with AKARI InfraRed Camera

We first obtained the spectrum of the diffuse Galactic light (DGL) at general interstellar space in 1.8-5.3 um wavelength region with the low-resolution prism spectroscopy mode of the AKARI Infra-Red Camera (IRC) NIR channel. The 3.3 um PAH band is detected in the DGL spectrum at Galactic latitude |b| < 15 deg, and its correlations with the Galactic dust and gas are confirmed. The correlation between the 3.3 um PAH band and the thermal emission from the Galactic dust is expressed not by a simple linear correlation but by a relation with extinction. Using this correlation, the spectral shape of DGL at optically thin region (5 deg < |b| < 15 deg) was derived as a template spectrum. Assuming that the spectral shape of this template spectrum is uniform at any position, DGL spectrum can be estimated by scaling this template spectrum using the correlation between the 3.3 um PAH band and the thermal emission from the Galactic dust.Comment: 7 pages, 5 figures, accepted by Publications of the Astronomical Society of Japan (PASJ

Search for the Infrared Emission Features from Deuterated Interstellar Polycyclic Aromatic Hydrocarbons

We report the results of a search for emission features from interstellar deuterated polycyclic aromatic hydrocarbons (PAHs) in the 4um region with the Infrared Camera (IRC) onboard AKARI. No significant excess emission is seen in 4.3-4.7um in the spectra toward the Orion Bar and M17 after the subtraction of line emission from the ionized gas. A small excess of emission remains at around 4.4 and 4.65um, but the ratio of their intensity to that of the band emission from PAHs at 3.3-3.5um is estimated as 2-3%. This is an order of magnitude smaller than the values previously reported and also those predicted by the model of deuterium depletion onto PAHs. Since the subtraction of the ionized gas emission introduces an uncertainty, the deuterated PAH features are also searched for in the reflection nebula GN 18.14.0, which does not show emission lines from ionized gas. We obtain a similar result that excess emission in the 4um region, if present, is about 2% of the PAH band emission in the 3um region. The present study does not find evidence for the presence of the large amount of deuterated PAHs that the depletion model predicts. The results are discussed in the context of deuterium depletion in the interstellar medium.Comment: 24 pages, 6 figures, to appear in Ap

Akari/irc near-infrared spectral atlas of galactic planetary nebulae

Near-infrared (2.5–5.0 μm) low-resolution (λ/Δλ ~ 100) spectra of 72 Galactic planetary nebulae (PNe) were obtained with the Infrared Camera (IRC) in the post-helium phase. The IRC, equipped with a 1' × 1' window for spectroscopy of a point source, was capable of obtaining near-infrared spectra in a slit-less mode without any flux loss due to a slit. The spectra show emission features including hydrogen recombination lines and the 3.3–3.5 μm hydrocarbon features. The intensity and equivalent width of the emission features were measured by spectral fitting. We made a catalog providing unique information on the investigation of the near-infrared emission of PNe. In this paper, details of the observations and characteristics of the catalog are describe

Unusual Carbonaceous Dust Distribution in PN G095.2+00.7

We investigate the polycyclic aromatic hydrocarbon features in the young Galactic planetary nebula PN G095.2+00.7 based on mid-infrared observations. The near- to mid-infrared spectra obtained with the AKARI/IRC and the Spitzer/IRS show the PAH features as well as the broad emission feature at 12 {\mu}m usually seen in proto-planetary nebulae (pPNe). The spatially resolved spectra obtained with Subaru/COMICS suggest that the broad emission around 12 {\mu}m is distributed in a shell-like structure, but the unidentified infrared band at 11.3 {\mu}m is selectively enhanced at the southern part of the nebula. The variation can be explained by a difference in the amount of the UV radiation to excite PAHs, and does not necessarily require the chemical processing of dust grains and PAHs. It suggests that the UV self-extinction is important to understand the mid-infrared spectral features. We propose a mechanism which accounts for the evolutionary sequence of the mid-infrared dust features seen in a transition from pPNe to PNe.Comment: 6 pages, 4 figure