Article

# Observations of the Near- to Mid-Infrared Unidentified Emission Bands in the Interstellar Medium of the Large Magellanic Cloud

(Impact Factor: 6.28). 09/2011; 744(1). DOI: 10.1088/0004-637X/744/1/68
Source: arXiv

ABSTRACT We present the results of near- to mid-infrared slit spectroscopic
observations (2.55--13.4 um) of the diffuse emission toward nine positions in
the Large Magellanic Cloud with the Infrared Camera (IRC) on board AKARI. The
target positions are selected to cover a wide range of the intensity of the
incident radiation field. The unidentified infrared bands at 3.3, 6.2, 7.7, 8.6
and 11.3 um are detected toward all the targets, and ionized gas signatures:
hydrogen recombination lines and ionic forbidden lines toward three of them. We
classify the targets into two groups: those without the ionized gas signatures
(Group A) and those with the ionized signatures (Group B). Group A includes
molecular clouds and photo-dissociation regions, whereas Group B consists of
HII regions. In Group A, the band ratios of I(3.3)/I(11.3), I(6.2)/I(11.3),
I(7.7)/$I(11.3) and$I(8.6)/$I(11.3) show positive correlation with the IRAS and AKARI colors, but those of Group B do not follow the correlation. We discuss the results in terms of the polycyclic aromatic hydrocarbon (PAH) model and attribute the difference to the destruction of small PAHs and an increase in the recombination due to the high electron density in Group B. In the present study, the 3.3 um band provides crucial information on the size distribution and/or the excitation conditions of PAHs and plays a key role in the distinction of Group A from B. The results suggest the possibility of the diagram of I(3.3)/I(11.3) v.s.$I(7.7)/\$I(11.3) as an efficient diagnostic tool
to infer the physical conditions of the interstellar medium.

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Available from: Hideki Umehata, Sep 02, 2014
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• "We find that the results do not depend on T * for T * =20,000–50,000 K because of the Lynman cut-off. See Mori et al. (2012) "
##### Conference Paper: Near- to Mid-Infrared Slit Spectroscopic Observations of the Unidentified Infrared Bands in the Large Magellanic Cloud
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ABSTRACT: We present the results of the near-infrared (NIR) to mid-infrared (MIR) slit spectroscopic observations of the diffuse emission toward nine positions in the nearby irregular galaxy Large Magellanic Cloud (LMC) with the Infrared Camera (IRC) on board AKARI. The unique characteristic of AKARI/IRC provides a great opportunity to analyze variations in the unidentified infrared (UIR) bands based on continuous spectra from 2.5 to of the same slit area. The observed variation of suggests destruction of small-sized UIR band carriers, polycyclic aromatic hydrocarbons (PAHs) in harsh environments. This result demonstrates that the UIR band provides us powerful information on the excitation conditions and/or the size distribution of PAHs, which is of importance for understanding the evolutionary process of hydrocarbon grains in the Universe. It also suggests a new diagnostic diagram of two band ratios, such as versus , for the interstellar radiation conditions. We discuss on the applicability of the diagnostic diagram to other astronomical objects, comparing the LMC results with those observed in other galaxies such as NGC 6946, NGC 1313, and M51.
The 2nd AKARI Conference; 11/2012
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##### Article: Detection of 3.3 Micron Aromatic Feature in the Supernova Remnant N49 with AKARI
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ABSTRACT: We present an infrared study of the supernova remnant (SNR) N49 in the Large Magellanic Cloud with the near-infrared (NIR; 2.5 - 5 {\mu}m) spectroscopic observations performed by AKARI. The observations were performed as a coarse spectral mapping to cover most of the bright region in the east, which enables us to compare the distribution of various line emission and to examine their correlation. We detect the 3.3 {\mu}m aromatic feature in the remnant, which is for the first time to report the presence of the 3.3 {\mu}m aromatic feature related to a SNR. In the line maps of H2 1-0 O(3), 3.3 {\mu}m feature, and Br{\alpha}, the distribution of the aromatic feature shows overall correlation with those of other emissions together with regional differences reflecting the local physical conditions. By comparison with other archival imaging data at different wavelengths, the association of the aromatic emission to other ionic/molecular emission is clarified. We examine archival Spitzer IRS data of N49 and find signatures of other polycyclic aromatic hydrocarbon (PAH) features at 6.2, 7.7, and 11.3 {\mu}m corresponding to the 3.3 {\mu}m aromatic feature. Based on the band ratios of PAHs, we find that PAHs in N49 are not only dominantly neutral but also small in size. We discuss the origin of the PAH emission in N49 and conclude that the emission is either from PAHs that have survived the shock or PAHs in the preshock gas heated by radiative precursor.
The Astrophysical Journal 09/2011; 744(2). DOI:10.1088/0004-637X/744/2/160 · 6.28 Impact Factor
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##### Article: The Central Region of the Barred Spiral Galaxy NGC 1097 Probed by AKARI Near-infrared Spectroscopy
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ABSTRACT: With the Infrared Camera on board AKARI, we carried out near-infrared (2.5-5.0 micron) spectroscopy of the central kiloparsec region of the barred spiral galaxy, NGC1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the area of ~50"*10" with the resolution of ~5", covering about a half of the ring and the galactic center. As a result, we spatially resolve the starburst ring in the polycyclic aromatic hydrocarbon 3.3 micron, the aliphatic hydrocarbon 3.4-3.6 micron features, and the hydrogen Br alpha 4.05 micron emission. They exhibit spatial distributions significantly different from each other, indicating that the environments vary considerably around the ring. In particular, the aliphatic features are enhanced near the bar connecting the ring with the nucleus, where the structure of hydrocarbon grains seems to be relatively disordered. Near the center, the continuum emission and the CO/SiO absorption features are strong, which indicates that the environments inside the ring are dominated by old stellar populations. The near-infrared spectra do not show any evidence for the presence of nuclear activity.
The Astrophysical Journal Letters 04/2012; 751(1). DOI:10.1088/2041-8205/751/1/L18 · 5.60 Impact Factor