NEAR-INFRARED HIGH-RESOLUTION SPECTROSCOPY OF THE OBSCURED AGN IRAS 01250+2832

Shirahata, M.,Usuda, T.,Oyabu, S.,Nakagawa, T.,Yamamura, I. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4

We provide a new physical insight on the hot molecular clouds near the nucleus of the heavily obscured AGN IRAS 01250+2832, based on the results of near-infrared high-resolution spectroscopy of gaseous CO ro-vibrational absorption lines with Subaru/IRCS. The detected CO absorption lines up to highly excited rotational levels reveal that hot dense molecular clouds exist around the AGN under the peculiar physical conditions.

NEAR-INFRARED SPECTROSCOPY OF CO RO-VIBRATIONAL ABSORPTION TOWARD HEAVILY OBSCURED AGNs

MAI SHIRAHATA,TAKAONAKAGAWA,SHINKI OYABU,Tomonori Usuda 한국천문학회 2017 天文學論叢 Vol.32 No.1

We provide a new physical insight on the hot molecular clouds near the nucleus of the obscured AGNs. We performed near-infrared spectroscopic observations of heavily obscured AGNsin order to reveal physical characteristics of molecular clouds,especially focused on the CO fundamental ro-vibrational absorption around 4.7 $\rm{\mu m}$. We have made systematic moderate-resolution spectroscopic observations toward 30 representative (U)LIRGsusing the {\it AKARI}/IRC, and some of the ULIRGs showed the strong CO absorption feature. For three bright (U)LIRGs that show a steep red continuum with the deep CO absorption feature,IRAS~08572$+$3915, UGC~05101, and IRAS~01250$+$2832, we have also made high-resolutionspectroscopic observations using the Subaru/IRCS. We have successfully detected many absorption linesup to highly excited rotational levels, and these lines are very deep and extremely broad. The derived physical conditions of molecular clouds are extreme; the gas temperatureis as high as several~100 to a 1000 K, the H$_2$ column density is larger than 10$^{22}$ $\rm{cm^{-2}}$,and the gas density is greater than 10$^7$ $\rm{cm^{-3}}$. Such hot and dense molecular cloudsmust exist around the central engine of the AGN.

The Newest Research of Alkaline Reduced Water

Sanetaka Shirahata,Takeki Hamasaki,Kiichro Teruya 한국물학회 2012 한국물학회지 Vol.3 No.1

Interfacial Strain Induced Magnetic Anisotropy of Epitaxial Fe₃O₄/BaTiO₃ Heterostructures

Yasuhiro Shirahata,Taiichiro Nozaki,Mitsuru Itoh,Tomoyasu Taniyama 한국자기학회 2010 한국자기학회 학술연구발표회 논문개요집 Vol.2010 No.12

DETECTION OF THE COSMIC FAR-INFRARED BACKGROUND IN AKARI DEEP FIELD SOUTH

Matsuura, S.,Shirahata, M.,Kawada, M.,Takeuchi, T. T.,Burgarella, D.,Clements, D. L.,Jeong, W.-S.,Hanami, H.,Khan, S. A.,Matsuhara, H.,Nakagawa, T.,Oyabu, S.,Pearson, C. P.,Pollo, A.,Serjeant, S.,Taka IOP Publishing 2011 The Astrophysical journal Vol.737 No.1

<P>We report new limits on the absolute brightness and spatial fluctuations of the cosmic infrared background (CIB) via the AKARI satellite. We carried out observations at 65, 90, 140, and 160 mu m as a cosmological survey in AKARI Deep Field South, which is one of the lowest cirrus regions with a contiguous area of the sky. After removing bright galaxies and subtracting zodiacal and Galactic foregrounds from the measured sky brightness, we successfully measured the CIB brightness and its fluctuations across a wide range of angular scales, from arcminutes to degrees. The measured CIB brightness is consistent with previous results reported from COBE data, but significantly higher than the lower limits at 70 and 160 mu m obtained via Spitzer from the stacking analysis of selected 24 mu m sources. The discrepancy with the Spitzer result is possibly due to a new galaxy population at high redshift obscured by hot dust or unknown diffuse emission. From a power spectrum analysis at 90 mu m, two components were identified: the CIB fluctuations with shot noise due to individual galaxies in a small angular scale from the beam size up to 10 arcminutes, and Galactic cirrus emission dominating at the largest angular scales of a few degrees. The overall shape of the power spectrum at 90 mu m is very similar to that at longer wavelengths, as observed by Spitzer and the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST). Our power spectrum, with an intermediate angular scale of 10-30 arcminutes, gives a firm upper limit for galaxy clustering, which was found by Spitzer and BLAST. Moreover, the color of the CIB fluctuations, which is obtained by combining our data with the previous results, is as red as ultra-luminous infrared galaxies at high redshift. These galaxies are not likely to provide the majority of the CIB emission at 90 mu m, but are responsible for the fluctuations. Our results provide new constraints on the evolution and clustering properties of distant infrared galaxies and any diffuse emission from the early universe.</P>

HIGHLY EXCITED CO LINES IN ACTIVE GALAXIES BOTH IN ABSORPTION AND IN EMISSION

TAKAO NAKAGAWA,Mai Shirahata,Tomonori Usuda 한국천문학회 2017 天文學論叢 Vol.32 No.1

In order to reveal physical conditions of molecular gas in active galaxies(“active galaxies” mean both starbursts and AGNs in this paper),we carried out systematic observations(R = 19 ~ 120) of CO fundamental band at 4.7 $\mu$m in absorption with\textit{AKARI}. We also made follow-upCO absorption observations at higher spectral resolution (R = 5000 ~ 1000) with \textit{Subaru}. Recently, \textit{Herschel}made extensive observations of highly-excited CO lines in emission in the far-infrared. The two datasets (absorption and emission) sometimes provide us with apparently inconsistent results. One case is starburst galaxies:\textit{Subaru} observations showed low temperature of molecular gas toward the starburstNGC253, while \textit{Herschel} detected highly excited CO lines in the starburst. This suggests that warmmolecular clouds are more deeply embedded than newly formed star clusters. The other case is obscured AGNs;\textit{Herschel} detected highly excited CO lines in emission in nearby AGNs,while \textit{AKARI} and\textit{Subaru} observations showed CO absorptiononly in some of the obscured AGNs. This could reflect the difference of nature of molecular tori in these AGNs. We propose the combination of the absorption and emission observationsas an effective tool to reveal geometry of warm molecular clouds in activegalaxies.

Element selective oxidation on Rh-Pd bimetallic alloy surfaces

Kondoh, Hiroshi,Toyoshima, Ryo,Shirahata, Naoki,Hoda, Asami,Yoshida, Masaaki,Amemiya, Kenta,Mase, Kazuhiko,Mun, Bongjin Simon The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.45

<P>The interactions between oxygen and Rh-Pd bimetallic alloy surfaces were investigated using surface sensitive experimental techniques and density functional theory calculations. The alloy surfaces were oxidized under 10<SUP>−5</SUP> Torr and 100 mTorr oxygen upon heating above 250 °C. A thin Rh oxide layer was preferentially formed on a Rh1Pd9(100) surface, while a thin Pd oxide layer was formed on a Rh1Pd9(111) surface, though the Rh oxide is thermodynamically more stable irrespective of the surface orientation. Chemical analyses revealed that the initial Rh fraction for the (111) surface was significantly lower than that for the (100) surface, which suggests that the oxidized element on the surface is kinetically selected depending on the near surface initial composition.</P>

AKARI IRC INFRARED 2.5-5 ㎛ SPECTROSCOPY OF NEARBY LUMINOUS INFRARED GALAXIES

Imanishi, Masatoshi,Nakagawa, Takao,Shirahata, Mai,Ohyama, Yoichi,Onaka, Takashi The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4

We present the result of systematic AKARI IRC infrared $2.5-5{\mu}m$ spectroscopy of >100 nearby luminous infrared galaxies, to investigate the energetic roles of starbursts and optically-elusive buried AGNs. Based on (1) the equivalent widths of the $3.3{\mu}m$ PAH emission features, (2) the optical depths of absorption features, and (3) continuum slopes, we can disentangle emission from starbursts and AGNs. We find that the energetic importance of buried AGNs increases with increasing galaxy infrared luminosities, suggesting that the AGN-starburst connections (and thereby possible AGN feedback to host galaxies) are luminosity dependent.

Photoluminescence, cytotoxicity and <i>in vitro</i> imaging of hexagonal terbium phosphate nanoparticles doped with europium

Di, Weihua,Li, Jie,Shirahata, Naoto,Sakka, Yoshio,Willinger, Marc-Georg,Pinna, Nicola Royal Society of Chemistry 2011 Nanoscale Vol.3 No.3

<P>Luminescent TbPO<SUB>4</SUB> nanoparticles were synthesized <I>via</I> a citric-acid-mediated hydrothermal route. Eu<SUP>3+</SUP> doping of TbPO<SUB>4</SUB> enables an efficient Tb<SUP>3+</SUP>-to-Eu<SUP>3+</SUP> energy transfer, leading to a four-fold increase of the absolute emission quantum yield (QY), compared to that of undoped TbPO<SUB>4</SUB>. To check the potential of biological use, we conducted <I>in vitro</I> biological experiments on human cervical carcinoma HeLa cells incubated with TbPO<SUB>4</SUB>:Eu nanoparticles. TbPO<SUB>4</SUB>:Eu nanoparticles can be successfully internalized into the cells, and they show bright intracellular luminescence and very low cytotoxicity. Photoluminescence intensity dependence upon time demonstrates that Eu<SUP>3+</SUP>-doped TbPO<SUB>4</SUB> nanoparticles are highly resistant to photobleaching. Our present work represents a demonstration of the use of rare-earth-based nanocrystals as a biological labeling agent because they combine several advantages including high emission quantum yield, long luminescence lifetime, low cytotoxicity and high photostability.</P> <P>Graphic Abstract</P><P>Highly luminescent TbPO<SUB>4</SUB> nanoparticles are obtained upon Eu<SUP>3+</SUP> doping due to an efficient Tb<SUP>3+</SUP>-to-Eu<SUP>3+</SUP> energy transfer. The biological experiments performed using HeLa cells demonstrate that our nanoparticles can be successfully internalized into the cells, and show bright intracellular luminescence, low cytotoxicity and high photostability. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0nr00673d'> </P>

PROBING STAR FORMATION IN ULTRALUMINOUS INFRARED GALAXIES USING AKARI NEAR-INFRARED SPECTROSCOPY

Kenichi Yano,TAKAO NAKAGAWA,Naoki Isobe,MAI SHIRAHATA 한국천문학회 2017 天文學論叢 Vol.32 No.1

We performed systematic observations of the \ion{H}{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 \ion{H}{i} recombination linesin ULIRGs with visual extinction higher than 15 mag. We detected the Br$\alpha$ line in 33 ULIRGs. In these galaxies, the relative contribution ofstarburst to the total infrared luminosity ($L_\mathrm{IR}$)is estimated on the basis of the ratio ofthe Br$\alpha$ line luminosity ($L_{\mathrm{Br}\alpha}$) to $L_\mathrm{IR}$. The mean $L_{\mathrm{Br}\alpha}/L_\mathrm{IR}$ ratioin LINERs or Seyfertsis significantly lower (~ 50%)than that in \ion{H}{ii} galaxies. This result indicates that active galactic nuclei contributesignificantly (~ 50%) to $L_\mathrm{IR}$ in LINERs,as well as Seyferts. We also estimate the absolutecontribution of starburst to $L_\mathrm{IR}$ using the ratio of star formation rates (SFRs)derived from $L_{\mathrm{Br}\alpha}$ (SFR$_{\mathrm{Br}\alpha}$) and those neededto explain $L_\mathrm{IR}$ (SFR$_\mathrm{IR}$). The mean SFR$_{\mathrm{Br}\alpha}/$SFR$_\mathrm{IR}$ratio is only 0.33 even in\ion{H}{ii} galaxies,where starburst is supposed to dominate the luminosity. We attribute this apparently low SFR$_{\mathrm{Br}\alpha}/$SFR$_\mathrm{IR}$ratio to the absorption ofionizing photons by dust within \ion{H}{ii} regions.