• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.135-139
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• 2017

We have performed systematic studies of the properties of dust in various environments of nearby galaxies with AKARI. The unique capabilities of AKARI, such as near-infrared (near-IR) spectroscopy combined with all-sky coverage in the mid- and far-IR, enable us to study processing of dust, particularly carbonaceous grains includings polycyclic aromatic hydrocarbons (PAHs), for unbiased samples of nearby galaxies. In this paper, we first review our recent results on individual galaxies, highlighting the uniqueness of AKARI data for studies of nearby galaxies. Then we present results of our systematic studies on nearby starburst and early-type galaxies. From the former study based on the near-IR spectroscopy and mid-IR all-sky survey data, we find that the properties of PAHs change systematically from IR galaxies to ultraluminous IR galaxies, depending on the IR luminosity of a galaxy or galaxy population. From the latter study based on the mid- and far-IR all-sky survey data, we find that there is a global correlation between the amounts of dust and old stars in early-type galaxies, giving an observational constraint on the origin of the dust.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.189-191
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• 2017

We performed systematic observations of the H $\small{I}$ $Br{\alpha}$ line ($4.05{\mu}m$) in 51 nearby (z<0.3) ultraluminous infrared galaxies (ULIRGs), using AKARI near-infrared spectroscopy. The $Br{\alpha}$ line is predicted to be the brightest among the H ${\small{I}}$ recombination lines in ULIRGs with visual extinction higher than 15 mag. We detected the $Br{\alpha}$ line in 33 ULIRGs. In these galaxies, the relative contribution of starburst to the total infrared luminosity ($L_{IR}$) is estimated on the basis of the ratio of the $Br{\alpha}$ line luminosity ($L_{Br{\alpha}}$) to $L_{IR}$. The mean $L_{Br{\alpha}}/L_{IR}$ ratio in LINERs or Seyferts is significantly lower (~50%) than that in H $\small{II}$ galaxies. This result indicates that active galactic nuclei contribute significantly (~50%) to $L_{IR}$ in LINERs, as well as Seyferts. We also estimate the absolute contribution of starburst to $L_{IR}$ using the ratio of star formation rates (SFRs) derived from $L_{Br{\alpha}}$ ($SFR_{Br{\alpha}}$) and those needed to explain $L_{IR}$ ($SFR_{IR}$). The mean $SFR_{Br{\alpha}}/SFR_{IR}$ ratio is only 0.33 even in H $\small{II}$ galaxies, where starburst is supposed to dominate the luminosity. We attribute this apparently low $SFR_{Br{\alpha}}/SFR_{IR}$ ratio to the absorption of ionizing photons by dust within H $\small{II}$ regions.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.321-324
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• 2012

Using extensive mid-IR datasets from AKARI, i.e. 9-band photometry covering the wavelength range from $2{\mu}m$ to $24{\mu}m$ and the unbiased spectroscopic survey for sources with $S_{\nu}$($9{\mu}m$)>0.3 mJy, we study starburst galaxies specifically at the redshift of z ~ 0.5, whose mid-IR spectra are clearly dominated by the PAH emission features. PAH-selected galaxies, selected with extremely red mid-IR colour due to PAHs, have high rest-frame PAH-to-stellar luminosity ratios, comparable to those in the most active regions in nearby starburst galaxies. Thus, they seem to have active starburst regions spreading over the whole body. Furthermore, some of PAH-selected galaxies are found to have peculiar rest-frame 11-to-$8{\mu}m$ flux ratios, which is systematically smaller than nearby starburst/AGN spectral templates. This may indicate a systematic difference in the physical condition of ISM between nearby and distant starburst galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.38.1-38.1
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• 2013

We present observational estimation of the infrared (IR) luminosity function (LF) of local (z < 0.3) star-forming (SF) galaxies derived from the AKARI NEP-Wide samples. We made an analysis of the NEP-Wide data with optical spectroscopic information allowing an accurate determination of luminosity function. Spectroscopic redshifts for about 1650 objects were obtained with MMT/Hectospec and WIYN/Hydra, and the median redshifts is about 0.22. To measure the contribution of SF galaxies to the luminosity function, we excluded AGN sample by comparing their SEDs with various model template. Spectroscopic redshifts and the AKARI's continuous filter coverage in the mid-IR (MIR) wavelength (2 ~ 25 micron) enable us to avoid large uncertainties from the mid-IR SED of galaxies and corresponding k-corrections. The 8-micron luminosity function shows a good agreement with the previous works in the bright-end, whereas it seems not easy to constrain the faint-end slope. The comparison with the results of the NEP-Deep data (Goto et al. 2010) suggests the luminosity evolution to the higher redshifts, which is consistent with the down-sizing evolutionary pattern of galaxies.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.185-187
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• 2017

Combining the AKARI Point Source Catalog and the 37-month Monitor of All-sky X-ray Image (MAXI) catalog, the infrared and X-ray properties of nearby active galactic nuclei were investigated. The 37-month MAXI catalog tabulates 100 nearby Seyfert galaxies, 73 of which are categorized into Seyfert I galaxies. Among these Seyfert galaxies, 69 ones were found to have an AKARI infrared counterpart. For the Seyfert I galaxies in this sample, a well-known correlation was found between the infrared and X-ray luminosities. However, the observed X-ray luminosity of the Seyfert II galaxies tends to be lower for the infrared luminosity than the Seyfert I galaxies. This suggests that the X-ray absorption is significant in the Seyfert II galaxies. The Seyfert II galaxies seem to have a bimodal distribution of the IR color between $18{\mu}m$ and $90{\mu}m$. Especially, a large fraction of the Seyfert II galaxies exhibits a redder IR color than the Seyfert I galaxies. A possible origin of the redder IR color is briefly discussed, in relation to the star formation activity in the host galaxy, and to the X-ray absorption.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.301-303
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• 2012

We present the result of our near infrared J- (${\lambda}=1.25{\mu}m$), H- (${\lambda}=1.63{\mu}m$), and $K_s$-band (${\lambda}=2.14{\mu}m$) imaging of ultraluminous ($L_{IR}$ > $10^{12}L_{\odot}$) and luminous ($L_{IR}=10^{11-12}L_{\odot}$) infrared galaxies (ULIRGs and LIRGs), to investigate their relationship through properties of their host galaxies. We find that (1) for single-nucleus ULIRGs and LIRGs, their spheroidal host galaxies have similar properties, but ULIRGs display a substantially higher level of nuclear activity than LIRGs, suggesting that their infrared luminosity difference comes primarily from the different level of current nuclear activity. We infer that LIRGs and ULIRGs have similar progenitor galaxies, follow similar evolutionary processes, and may evolve into optically-selected QSOs. (2) Largely-separated multiple-nuclei ULIRGs have significantly brighter host galaxies than single-nucleus ULIRGs and LIRGs in $K_s$-band, indicating that multiple-nuclei ULIRGs have a bias towards mergers of intrinsically large progenitor galaxies, in order to produce high infrared luminosity ($L_{IR}$ > $10^{12}L_{\odot}$) even at the early merging stage. (3) We derive dust extinction of host galaxies of ULIRGs and LIRGs to be $A_V$ ~ 14 mag in the optical or equivalently $A_K$ ~ 0.8 mag in the near-infrared $K_s$-band, based on the comparison of host galaxy's luminosities in the J-, H-, and $K_s$-bands.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.72.3-72.3
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• 2015

We present the mid-infrared (MIR) luminosity function (LF) of local (z < 0.3) star forming (SF) galaxies based on the AKARI's NEP-Wide Survey data. We utilized a combination of the NEP-Wide point source catalogue containing a large number (114,000) of infrared (IR) sources distributed over the wide (5.4 sq. deg) field and spectroscopic redshift (z) data for 1790 selected targets obtained by optical follow-up surveys with MMT/Hectospec and WIYN/Hydra. The AKARI's continuous $2{\sim}24{\mu}m$ wavelength coverage and the spectroscopic redshifts for sample galaxies enable us to derive accurate spectral energy distributions (SEDs) in the mid-infrared. We carried out SED-fit analysis and employed 1/Vmax method to derive the mid-IR (e.g., $8{\mu}m$, $12{\mu}m$, and $15{\mu}m$ rest-frame) luminosity functions. Our results for local galaxies from the NEP region generally consistent with various previous works for other fields over wide luminosity ranges. The comparison with the results of the NEP-Deep data implies the luminosity evolution from higher redshifts towards the present epoch. We attempted to fit our derived LFs to the double power-laws and present the resulting power indices. We also examined the correlation between mid-IR luminosity and total IR luminosity.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.69.2-69.2
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• 2014

We present space-based near-IR (NIR) and optical photometry of globular clusters (GCs) of 16 early-type galaxies in the Fornax and Virgo Clusters. The NIR imaging data for the nearby galaxies was acquired with the IR Channel of the Wide Field Camera 3 (WFC3/IR) in the F110W ($J_{110}$) and F160W ($H_{160}$) bandpasses. We introduce the full sample of our WFC3/IR program, describe data reductions and photometric measurements including GC candidate selection criteria, and then show selected GCs' color-magnitude diagrams. The tilted features in the diagrams related to the morphological types of host galaxies are discussed in the context of galaxy formation and evolution histories. Combining F475W ($g_{475}$) and F850LP ($z_{850}$) data taken from the Advanced Camera for Surveys Virgo and Fornax Cluster Surveys with our NIR data, we investigate the bimodality in optical-NIR color distribution and the nonlinear feature of the optical-NIR color relation as a function of optical color for these extragalactic GC systems.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.317-320
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• 2012

A sample of nearby galaxies was built from the AKARI/FIS all sky survey cross-correlated with the SDSS and GALEX surveys. The spectral energy distributions from 0.15 to 160 microns of these galaxies are analysed to study dust attenuation and star formation properties. The calibrations of the amount of dust attenuation as a function of the IR-to-UV flux ratio and the FUV-NUV colour are re-investigated: the former one is confirmed to be robust and accurate whereas the use of the FUV-NUV colour to measure dust attenuation is found highly uncertain. The current star formation rate given by the SED fitting process is compared to that directly obtained from the UV and total IR luminosities. It leads to an accurate estimate of dust heating by old stars. We emphasize the importance of such a sample as a reference for IR selected star forming galaxies in the nearby universe.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.40.2-40.2
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• 2010

Polycyclic aromatic hydrocarbon (PAH) features have emerged as one of the most important infrared (IR) features since these PAH features dominate mid-IR spectra of galaxies and are ubiquitous within galactic and extragalactic objects. These PAH features have the potentials to become reliable star formation rate (SFR) proxies and diagnostics of physical conditions of interstellar medium, such as ionization states of dust grains and grain sizes. While constructing an unbiased library of 44 sample galaxies selected from 5MUSES sample, AKARI mJY Unbiased Survey of Extragalactic Sources in 5MUSES (AMUSES) intends to measure and to calibrate the PAH 3.3 mm emission feature which has not been studied extensively due to its weak strength and dearth of capable instruments. Out of 20 target galaxies, we detected the 3.3mm feature from eight galaxies and measured their line strengths, line widths and line ratios with other PAH emission features. Sample galaxies whose spectral energy distributions (SEDs) are classified as starburst-type have clearly stronger 3.3mm emission features than ones with AGN-type SEDs. We also found that there is a correlation between the PAH 3.3mm luminosity and total IR luminosity within our sample galaxies, albeit a large scatter. We further discuss implications of our results.