AKARI observations of interstellar dust grains in our Galaxy andnearby galaxies

H. Kaneda a,n, D. Ishihara a, K. Kobata a, T. Kondo a, S. Oyabu a, R. Yamada a, M. Yamagishi a,T. Onaka b, T. Suzuki c

a Graduate School of Science, Nagoya University, Nagoya 464-8602, Japanb Department of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japanc Netherlands Institute for Space Research, SRON, Utrecht, The Netherlands

a r t i c l e i n f o

Article history:Received 11 October 2013Received in revised form30 December 2013Accepted 20 January 2014

Keywords:Intersteller dustPAHGalaxyAKARI

a b s t r a c t

The infrared (IR) emission from interstellar dust grains is a powerful tool to trace star-formation activities ingalaxies. Beyond such star-formation tracers, spectral information on polycyclic aromatic hydrocarbons(PAHs) and large grains, or even their photometric intensity ratios, has deep physical implications forunderstanding the properties of the interstellar medium. With the AKARI satellite launched in 2006, we haveperformed a systematic study of interstellar dust grains in various environments of galaxies including ourGalaxy. Because of its unique capabilities, such as mid-/far-IR all-sky surveys and near-/far-IR spectroscopy,AKARI has provided new knowledge on the processing of dust, particularly carbonaceous grains includingPAHs, in the interstellar space. For example, the near-IR spectroscopy has revealed structural changes ofhydrocarbon grains in harsh environments of galaxies. In this paper, we focus on the properties of the PAHemission obtained by the AKARI mid-IR all-sky survey and near-IR spectroscopy.

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1. Introduction

In star-forming regions, large grains and polycyclic aromatichydrocarbons (PAHs; i.e., smallest form of carbonaceous grains) absorba significant fraction of stellar ultraviolet photons and re-radiate themin the infrared (IR). Hence the IR luminosities due to PAHs and largegrains are both powerful tools to trace star-forming activities ingalaxies or search for young stellar objects embedded in clouds.However they are not merely star-formation tracers. Spectral informa-tion on PAHs and large grains, as well as relative abundance of PAHs tolarge grains, would have much deeper physical implications forunderstanding the properties of the interstellar medium (ISM).

With the Infrared Camera (IRC; Onaka et al., 2007) and the Far-Infrared Surveyor (FIS; Kawada et al., 2007) on board AKARI, thefirst Japanese infrared astronomical satellite launched in 2006(Murakami et al., 2007), we have performed a systematic study ofinterstellar dust grains in various environments of galaxies includ-ing our Galaxy. Because of its unique capabilities, such as all-skycoverage in the mid- and the far-IR combined with near- and far-IRspectroscopy, AKARI has provided new knowledge on the proces-sing of dust, particularly carbonaceous grains including PAHs, in theinterstellar space.

For example, we obtained all-sky diffuse maps in the 9, 18, 65,90, 140, and 160 μm photometric bands by the all-sky surveys.

Among them, the 9 μm diffuse map is the world-first all-sky mapof the PAH emission, while the other maps mostly trace warm andcool components of large grains. In addition to such photometricdatasets, we obtained near-IR (2–5 μm) spectroscopic data formore than 10,000 targets by pointed observations (Ohyamaet al., 2007), most of which were performed during the warmmission phase after the boil-off of liquid helium cryogen. We alsoobtained far-IR (70–170 μm) spectroscopic data using the imagingFourier Transform Spectrometer of the FIS (Kawada et al., 2008).For example, the near- and the far-IR spectroscopy have revealedstructural changes of hydrocarbon particles (e.g., Yamagishi et al.,2012) and formation of large graphite grains (Kaneda et al., 2012b),respectively, in harsh environments of galaxies.

In this paper, we focus on the properties of the PAH emissionobtained by the AKARI mid-IR all-sky survey and near-IR spectro-scopy. We discuss (1) spatial variations in the photometric inten-sity of the mid-IR emission due to PAHs relative to that of thefar-IR emission due to large grains, based on the all-sky diffusemaps, and (2) spectral variations in the ratio of the aliphatic to thearomatic feature, based on the near-IR spectra.

2. All-sky survey in the mid-IR PAH emission

Fig. 1a displays a diffuse map of the Galactic plane in the AKARI9 μm band. It should be noted that the AKARI 9 μm band (thereference wavelength and the band width of 9.0 μm and6.7–11.6 μm respectively; Onaka et al., 2007) efficiently covers

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n Corresponding author. Tel.: þ81 52 7892452.E-mail address: kaneda@u.phys.nagoya-u.ac.jp (H. Kaneda).

Please cite this article as: Kaneda, H., et al., AKARI observations of interstellar dust grains in our Galaxy and nearby galaxies. Planetaryand Space Science (2014), http://dx.doi.org/10.1016/j.pss.2014.01.017i

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the major PAH emission features at wavelengths of 6.3, 7.7, 8.6,and 11.3 μm, as compared to the all-sky maps in the WISE or IRASbands at similar wavelengths (Ishihara et al., 2010a). Fig. 1b showsa correlation plot between the AKARI 9 μm and 140 μm bandintensities for the all-sky images regridded to a spatial scale of60 arc m�60 arc m. The plot exhibits a tight correlation over arange of 4 orders of magnitude with the linear-correlation coeffi-cient of 0.94. This correlation demonstrates that PAHs and largegrains are mixed well in the ISM, as pointed out by many authors(e.g., Onaka et al., 1996; Kaneda et al., 2012a).

Utilizing the AKARI all-sky point-source catalogs, we derivedthe spatial distributions of carbon-rich (C-rich) and oxygen-rich(O-rich) asymptotic giant branch (AGB) stars, based on the color–color diagrams of the 9 and 18 μm band fluxes with the 2MASS J, H,and K band fluxes (Ishihara et al., 2011). As a result, we find thatthe O-rich AGBs are more concentrated toward the Galactic center,while the C-rich AGBs are rather uniformly distributed throughoutthe Galactic plane. As can be seen in Fig. 1b, interstellar PAHs andfar-IR dust grains are similar in the spatial distribution on bothglobal and local scales, which do not follow well the distributionof either C-rich or O-rich stars. It is generally thought that silicategrains, a major far-IR dust component, are supplied into theinterstellar space by O-rich stars, while carbonaceous grainsincluding PAHs are produced by C-rich stars (e.g., Dwek, 1998).Thus our results show that PAHs and large grains are well mixedin the ISM whereas their suppliers have different spatial distribu-tions. It is also worth to note that variation of the 3.4 μm aliphatichydrocarbon absorption feature seems to follow that of the 9.7 μm

amorphous silicate absorption feature; their optical depths relativeto the visual extinction in the Galactic center are both about twiceas large as those in the local diffuse interstellar medium (Gao et al.,2010). This is an open issue to be addressed in future works.

Hence the AKARI 9 μm map reveals that PAHs are widely dis-tributed throughout the Galactic plane, similar to large grains. Yet themaps also exhibit significant variations in the relation between thePAH and the far-IR dust emission, depending on local interstellarconditions. For example, in shocked regions associated with supernovaremnants (SNRs), PAH emission is extremely suppressed as comparedto far-IR dust emission (e.g., Ishihara et al., 2010b), which is attributedto a large difference in the lifetime against strong shocks betweenPAHs and large grains (Micelotta et al., 2010). In post-shock hotplasmas, lifetimes of PAHs are two to three orders of magnitudeshorter than those for equivalent dust grains of roughly the same size,because the sputtering yields of 3-dimensional grains (i.e. the numberof sputtered atoms per incident high-energy particle) are muchsmaller than unity, while the dissociation yields of 2-dimensionalPAHs are close to unity. Other than SNRs, Kaneda et al. (2012a) foundthat the ratios of the PAH to far-IR dust emission show a significantdepression (by a factor of � 5) near the foot points of the molecularloops revealed by the NANTEN 12CO ðJ ¼ 1�0Þ observations in theGalactic center region (Fukui et al., 2006). Because the CO observationsindicated that a violent motion and shock heating of gas took place inthe loops (Torii et al., 2010), the relative decrease in the PAH emissionsuggests the destruction of PAHs by shocks at the foot points of themolecular loops.

External galaxies provide much wider ranges of physical con-ditions for the ISM than our Galaxy. Among them, nearby edge-onstarburst galaxies with prominent galactic superwinds are impor-tant targets to understand the processing of dust in high energeticphenomena. For example, in M 82 (Kaneda et al., 2010) and NGC253 (Kaneda et al., 2009), we find that copious amounts of largegrains and PAHs are flowing out of the galaxies by galacticsuperwinds, both of which are likely being shattered anddestroyed in the galactic haloes. Fig. 2a and b shows correlationplots between the AKARI 9 μm and 140 μm band intensities for M82 and NGC 253, respectively, where the different symbols andcolors are used to discriminate the center, disk, northern andsouthern halo regions. In each panel, the solid line represents therelationship obtained for our Galaxy (i.e., Fig. 1b). As can be seen inthe figure, they exhibit global relations quite similar to our Galaxy,despite the fact that the environments are much harsher in thesegalaxies. In the halo regions, it appears that the 9 μm to 140 μmratios are systematically shifted toward lower values. Moreoverthe data points for NGC 253 exhibit an apparently larger scatterthan those for M 82, which may reflect that NGC 253 is a starburstgalaxy in a later evolutionary stage than M 82, causing differencein the degree of the dust processing. In the center of M 82, the9 μm to 140 μm ratios are well above the other regions, which islikely to be caused by a large increase in interstellar radiation fieldintensity (see Fig. 13 in Draine and Li, 2007).

In interpreting the above results, we have to take into accountthe photo-dissociation of PAHs exposed to a strong ultraviolet (UV)radiation field (Boulanger et al., 1988; Bendo et al., 2008), althoughit is much less effective than destruction by shocks; the lifetimes ofPAHs against the photo-dissociation are 105 years in massive star-forming regions, while they are 108 years for the diffuse ISM(Allain et al., 1996). Even for a constant abundance ratio of PAHs tolarge grains, the 9 μm to 140 μm intensity ratio will change withother parameters such as the UV radiation field and dust extinc-tion (Kaneda et al., 2012a). The ratios increase with the UVradiation field as long as it is stronger than that in the solarneighborhood (Draine and Li, 2007). Larger interstellar extinctionin the mid-IR than in the far-IR can systematically lower the ratiosof 9 μm to 140 μm intensities in dense gas regions. The dominance

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Fig. 1. (a) AKARI 9 μm-band all-sky diffuse map in the galactic coordinates, showntogether with the observational positions of AKARI near-IR (2–5 μm) spectroscopy.(b) A correlation plot between the AKARI 9 μm and 140 μm band intensities for theall-sky images regridded to a spatial scale of 60 arc m�60 arc m.

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of neutral PAHs over ionized ones in very dense gas regions canalso lower the ratios, because neutral PAHs emit much less in the6–9 μm region than ionized PAHs (Szczepanski and Vala, 1993;Joblin et al., 1994; Hudgins and Allamandola, 1995). Condensationof PAHs in grain ice mantles would also be an important factor inlowering the relative intensity of the PAH emission features indense gas regions. In short, even for a constant relative abundanceof PAHs, the 9 μm to 140 μm intensity ratio can decline in UV-poor,dense gas regions, the situation of which does not seem to beapplicable to the cases presented above.

3. Spectroscopy of the near-IR PAH emission

In Fig. 1a, we plot the positions of the AKARI near-IR spectro-scopic observations. The properties of PAHs are probed by thespectroscopy of the 3.3 μm feature and the 3.4–3.5 μm features.Both of them are attributed to the C–H stretching vibration. Theformer is due to aromatic (sp2) hydrocarbons, while the latteris attributed to aliphatic (sp3) hydrocarbons (e.g., Duley andWilliams, 1981; Wagner et al., 2000). To be exact, the 3.4–3.5 μmfeature intensities give upper limits on the aliphatic fractions inhydrocarbon grains (Li and Draine, 2012; Yang et al., 2013). The

aromatic feature at 3.3 μm is sensitive to smallest PAHs (Schutteet al., 1993), as compared to the other PAH features at longerwavelengths.

For about 200 star-forming galaxies in a redshift range of�0.01–0.1, we systematically investigated a global relation betweenthe PAH 3.3 μm luminosity, L3:3, and the total IR (8–1000 μm)luminosity, LIR (Yamada et al., 2013). We classified the samples intoIR galaxies (IRGs; LIRo1011L� ), luminous IR galaxies (LIRGs:LIR � 1011�1012L� ) and ultra-luminous IR galaxies (ULIRGs:LIR41012L� ). M82 is categorized into IRGs. We confirm that manyof the IRGs and LIRGs follow the relationship, L3:3=LIRC10�3,which is a ratio typical of starburst galaxies (Mouri et al., 1990).However we also find that the L3:3=LIR ratio considerably decreasestoward the luminous end in the ULIRG population. We concludethat local ULIRGs intrinsically possess smaller amounts of PAHsrelative to large grains, as a result of PAH processing through recentgalaxy mergers. Some fraction of PAHs may have been destroyedonce by a shock induced during a merging process, whereas largegrains survive. Hence our result is consistent with the observationalfact that local ULIRGs are merging galaxies (e.g., Clements et al.,1996). Considering a starburst age typical of local ULIRGs (�10–100Myr; Genzel et al., 1998) as well as a lifetime of intermediate-massstars (�100–1000 Myr) responsible for the production of PAHs attheir late stages, it is unlikely that PAHs have been reproduced andreplenished by the stars that were newly born after the merger.Therefore the observed PAHs are likely to be merger remnants inlocal ULIRGs.

The intensity ratios of the aliphatic to the aromatic feature areknown to show regional variations in the ISM. A huge dataset ofAKARI near-IR spectroscopy reveals that they indeed change verymuch, depending on the interstellar conditions, which impliesstructural changes of hydrocarbon grains. Fig. 3 displays examplesof the spectra with relatively normal aliphatic/aromatic ratios,while Fig. 4 shows those with unusually high aliphatic/aromaticratios. As for Galactic sources, comparing the spectra in Figs. 3aand 4a, we find that the spectrum for the foot point of themolecular loop in the Galactic center region has spectral proper-ties notably different from a typical Galactic diffuse spectrum at3.2–3.6 μm; the properties in Fig. 4a are characterized by the faintPAH 3.3 μm emission and the broad excess above the linearbaseline (Kaneda et al., 2012a). The broad excess may be explainedby a combination of a series of the features at 3.47, 3.51, and3.56 μm accompanying the 3.4 μm aliphatic feature (e.g., Sloanet al., 1997). Assuming that all the features are due to aliphaticC–H, the spectrum suggests that hydrogenated amorphous carbongrains may have been produced near the foot point of themolecular loop by shattering of larger carbonaceous grains(Jones et al., 1996), while pre-existing small PAHs may have beendestroyed there. These hydrocarbon grains are likely to be H-richand aliphatic-rich, and have not yet been evolved into H-poor,aromatic-rich materials (Jones et al., 2013); the aromatizationrequires subsequent UV radiation and/or thermal annealing.

For M 82, we clearly detect the aromatic 3.3 μm emission andthe aliphatic 3.4–3.6 μm features even in the galactic halo regions,which are located at a distance of 2 kpc away from the galacticcenter (Yamagishi et al., 2012). We thus confirm the presence ofPAHs even in the harsh environment of the M82 halo. We find thatthe aliphatic 3.4–3.5 μm features are unusually abundant in thehalo spectra, comparing Fig. 4b and c with Fig. 3b and c. Thespectra of 34 regions in M 82 reveal that the aliphatic/aromaticratio significantly increases with the distance from the galacticcenter (Yamagishi et al., 2012), which again indicates the dom-inance of aliphatic structures over aromatic ones by shattering ofhydrogenated amorphous carbon grains in the galactic superwind.As for the mid-IR PAH emission, we found that there is anexcellent correlation between the PAH and Hα distributions

Fig. 2. (a) A correlation plot between the AKARI 9 μm and 140 μm band intensitiesfor M 82, where the images in both bands are regridded to a spatial scale of90 arc s�90 arc s. (b) Same as panel (a), but for NGC 253. The plus (black),diamond (green), triangle (blue), and square (magenta) symbols correspond todata points for the galactic center, disk, northern halo, and southern halo regions,respectively. In each panel, the solid line represents the relationship for our Galaxy.(For interpretation of the references to color in this figure caption, the reader isreferred to the web version of this paper.)

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extended in the halo (Kaneda et al., 2010). The spectro-polarimetryshowed that Hα is significantly (5–15%) polarized (Yoshida et al.,2011), implying that Hα photons from the galactic disk arescattered by dust grains in the halo. Thus the excellent PAH–Hαcorrelation can be explained if the grains are being fragmented toproduce PAHs by the galactic superwinds (Jones et al., 1996, 2013).Moreover the estimated dust flow velocity was found to decreasewith the height from the disk (Yoshida et al., 2011), suggesting thatthe grains thus processed may be falling back toward the disk.

We also detect strong aliphatic emission from the centralregion of the barred spiral galaxy NGC 1097 (Kondo et al., 2012).The galaxy is categorized as Seyfert 1 with the starburst ring of2 kpc in diameter and the inner bar structure of 1 kpc in lengthconnecting the ring and the nucleus (Hsieh et al., 2008). HenceNGC 1097 is an ideal laboratory to study the ISM in galaxiesshowing both active galactic nucleus (AGN) and circumnuclearstarburst activities. Figs. 3d and 4d present the spectra for thestarburst ring and inner bar regions in NGC 1097, respectively,from which we find that the spectrum taken from the inner barexhibits a relatively high aliphatic/aromatic ratio. By spectralmapping in the 3.3 μm feature and the 3.4–3.5 μm features, wefind that the distribution of the aliphatic relative to the aromaticfeature spatially corresponds to the inner bar connecting the ringand the nucleus (Kondo et al., 2012). Thus the local enhancementsof the aliphatic features are, again, consistent with the picture thatsmall hydrocarbon grains, not much aromatized, may be newlyformed through shattering of carbonaceous grains in the inner bar(Jones et al., 1996, 2013), which might provide observational

evidence that the gas and dust in the bar is in a turbulent motion,likely fueling the central AGN from the starburst ring.

Among the afore-mentioned AKARI near-IR spectral sampleof star-forming galaxies, Fig. 3e and f presents examples ofthe spectra of IRGs and LIRGs, respectively, with relatively normalaliphatic/aromatic ratios, while Fig. 4e and f shows those withunusually high aliphatic/aromatic ratios. A significant fraction ofthe LIRG and ULIRG samples is found to exhibit similarly highaliphatic/aromatic ratios. However we do not find any cleardependence of the aliphatic/aromatic ratio on LIR or the galaxypopulation. The variation of the ratio can be explained bydifference in the scale of the past merger, i.e., minor or major, ordifference in the stage of the current merging process. Since mostof the sample galaxies are not spatially resolved, it is notable thatnot only particular regions in galaxies but also galaxies as a wholeexhibit such unusually high aliphatic/aromatic ratios.

We estimate the ratios of the integrated intensities of thealiphatic to the aromatic feature to be 0.1–0.4 for the spectra inFig. 3 and 0.6–3 for the spectra in Fig. 4. Using A3:4=A3:3C1:76(Yang et al., 2013), where A3:3 and A3:4 are the band strengths ofthe 3.4 μm aliphatic and 3.3 μm aromatic C–H bonds, along withthe assumption that one aliphatic and one aromatic C atomcorrespond to 2.5 aliphatic and 0.75 aromatic C–H bonds, respec-tively (Yang et al., 2013), we derive the fraction of C atoms inaliphatic form to be 2–7% for the spectra in Fig. 3 and 10–50% forthe spectra in Fig. 4. Thus a significant fraction of C atoms are inaliphatic form for the latter (Fig. 4), while they are predominantlyaromatic for the former targets (Fig. 3). It should be noted,

Fig. 3. AKARI near-IR spectra with relatively normal aliphatic/aromatic ratios: (a) Galactic diffuse emission observed at the galactic longitude of � 311:51, (b) center and(c) disk in M 82, (d) starburst ring in NGC 1097, (e) J1224360þ392258 (IRG), and (f) J1456077þ833122 (LIRG). All the spectra are shown in the observed, but not rest-framewavelengths. The emission at �4.05 μm is the hydrogen Brα line.

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however, that a significant fraction of aromatic or aliphatic Catoms can be locked inside of grains, which cannot be probed bythe 3.3 and 3.4–3.5 μm emission features. As pointed out by Yanget al. (2013), in benign, UV-poor environments, fragile species suchas aliphatic hydrocarbon chains tend to attach to an aromaticskeleton as side groups. Therefore we can expect that PAHs arerich with aliphatic chains in quiescent ISM conditions. Our AKARIresults on interstellar PAHs in galaxies, however, appear to favorrather opposite situations for the presence of aliphatic-rich PAHs,i.e. they are detected in harsh interstellar environments, thepresence of which can be explained by shock fragmentation ofgrains with carbonaceous mantles (Jones et al., 2013).

4. Summary

With the AKARI's unique capabilities of mid-/far-IR all-skysurveys and near-IR spectroscopy, we have revealed variousphenomena about interstellar dust grains in galaxies includingour Galaxy. Based on the all-sky maps, we find that the intensityratios of PAHs to far-IR large grains systematically decrease inharsh environments, which can be used as probes to study theconditions of interstellar shocks on both global and local scales.With the near-IR spectroscopy we find that the ratios of thealiphatic to aromatic feature strength considerably change,depending on the interstellar conditions; all the cases presentedabove indicate structural changes of hydrocarbon grains by shocksin harsh interstellar environments.

The researches presented in this paper are based on observationsmade with AKARI, a JAXA project with the participation of ESA.

References

Allain, T., Leach, S., Sedlmayr, E., 1996. Astron. Astrophys. 305, 602.Bendo, G.J., et al., 2008. Mon. Not. R. Astron. Soc. 389, 629.Boulanger, F., Beichman, C., Désert, F.X., Helou, G., Pérault, M., Ryter, C., 1988.

Astrophys. J. 332, 328.Clements, D.L., Sutherland, W.J., McMahon, R.G., Saunders, W., 1996. Mon. Not. R.

Astron. Soc. 279, 477.Draine, B.T., Li, A., 2007. Astrophys. J. 657, 810.Duley, W.W., Williams, D.A., 1981. Mon. Not. R. Astron. Soc. 196, 269.Dwek, E., 1998. Astrophys. J. 501, 643.Fukui, Y., et al., 2006. Science 314, 106.Gao, J., Jiang, B.W., Li, A., 2010. Earth Planets Space 62, 63.Genzel, R., et al., 1998. Astrophys. J. 498, 579.Hsieh, P.-Y., Matsushita, S., Lim, J., Kohno, K., Sawada-Satoh, S., 2008. Astrophys.

J. 683, 70.Hudgins, D.M., Allamandola, L.J., 1995. J. Phys. Chem. 99, 3033.Ishihara, D., et al., 2010a. Astron. Astrophys. 514, 1.Ishihara, D., et al., 2010b. Astron. Astrophys. 521, L61.Ishihara, D., et al., 2011. Astron. Astrophys. 534, A79.Joblin, C., D'Hendecourt, L., Leger, A., Defourneau, D., 1994. Astron. Astrophys. 281,

923.Jones, A.P., Tielens, A.G.G.M., Hollenbach, D.J., 1996. Astrophys. J. 469, 740.Jones, A.P., Fanciullo, L., Köhler, M., Verstraete, L., Guillet, V., Bocchio, M., Ysard, N.,

2013. Astron. Astrophys. 558, A62.Kaneda, H., Yamagishi, M., Suzuki, T., Onaka, T., 2009. Astrophys. J. 698, L125.Kaneda, H., et al., 2010. Astron. Astrophys. 514, A14.Kaneda, H., et al., 2012a. Publ. Astron. Soc. Jpn. 64, 25.Kaneda, H., et al., 2012b. Astron. Astrophys. 543, A79.Kawada, M., et al., 2007. Publ. Astron. Soc. Jpn. 59, 389.Kawada, M., et al., 2008. Publ. Astron. Soc. Jpn. 60, 389.

Fig. 4. AKARI near-IR spectra with unusually high aliphatic/aromatic ratios: (a) the foot point of one of the molecular loops in the Galactic center region, (b) southern and(c) northern haloes in M 82, (d) inner bar in NGC 1097, (e) J0055449-502749 (IRG), and (f) NGC 3110 (LIRG). All the spectra are shown in the observed, but not in rest-framewavelengths. In panel (a), instrumental artifacts are masked out.

H. Kaneda et al. / Planetary and Space Science ∎ (∎∎∎∎) ∎∎∎–∎∎∎ 5

Please cite this article as: Kaneda, H., et al., AKARI observations of interstellar dust grains in our Galaxy and nearby galaxies. Planetaryand Space Science (2014), http://dx.doi.org/10.1016/j.pss.2014.01.017i

Kondo, T., et al., 2012. Astrophys. J. 751, L18.Li, A., Draine, B.T., 2012. Astrophys. J. 760, L35.Micelotta, E.R., Jones, A.P., Tielens, A.G.G.M., 2010. Astron. Astrophys. 510, A37.Mouri, H., Kawara, K., Takeushi, Y., Nishida, M., 1990. Astrophys. J. 356, L39.Murakami, H., et al., 2007. Publ. Astron. Soc. Jpn. 59, 369.Ohyama, Y., et al., 2007. Publ. Astron. Soc. Jpn. 59, 411.Onaka, T., Yamamura, I., Tanabé, T., Roellig, T.L., Yuen, L., 1996. Publ. Astron. Soc. Jpn.

48, L59.Onaka, T., Matsuhara, H., Wada, T., et al., 2007. Publ. Astron. Soc. Jpn. 59, 401.Schutte, W.A., Tielens, A.G.G.M., Allamandola, L.J., 1993. Astrophys. J. 415, 397.

Sloan, G.C., Bregman, J.D., Geballe, T.R., Allamandola, L.J., Woodward, C.E., 1997.Astrophys. J. 474, 735.

Szczepanski, J., Vala, M., 1993. Astrophys. J. 414, 646.Torii, K., et al., 2010. Publ. Astron. Soc. Jpn. 62, 675.Wagner, D.R., Kim, H.S., Saykally, R.J., 2000. Astrophys. J. 545, 854.Yamagishi, M., et al., 2012. Astron. Astrophys. 541, 10.Yoshida, M., Kawabata, K.S., Ohyama, Y., 2011. Publ. Astron. Soc. Jpn. 63, 493.Yamada, R., Oyabu, S., Kaneda, H., Yamagishi, M., Ishihara, D., Kim, J.-H., Im, M.,

2013. Publ. Astron. Soc. Jpn. 65, 103.Yang, X.J., Glaser, R., Li, Aigen, Zhong, J.X., 2013. Astrophys. J. 776, 110.

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