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.

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.

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.

AKARI INFRARED CAMERA OBSERVATIONS OF THE 3.3 μm PAH FEATURE IN Swift/BAT AGNs

Angel Castro,Takamitsu Miyaji,MAI SHIRAHATA,Kohei Ichikawa,SHINKI OYABU,David Clark,Masatoshi Imanishi,TAKAO NAKAGAWA,Yoshihiro Ueda 한국천문학회 2017 天文學論叢 Vol.32 No.1

Using the InfraRed Camera (IRC) on board the infrared astronomical satellite {\sl AKARI} we study the 3.3 $\mu$mpolycyclic aromatic hydrocarbon (PAH) feature and its connection to active galactic nucleus (AGN) propertiesfor a sample of 54 hard X-­ray selected bright AGN, including both Seyfert 1 and Seyfert 2 type objects. The sample is selected from the 9-­month {\sl Swift}/BAT survey in the 14--­195 keV band and all of the sources have known neutralhydrogen column densities ($N_{\rm H}$). The 3.3 $\mu$m PAH luminosity ($L_{\rm 3.3{\mu}m}$) is used as a proxy for star-formation (SF)activity and hard X-ray luminosity ($L_{\rm 14-195keV}$) as an indicator of the AGN power. We explore for possible difference of SFactivity between type 1 (un-absorbed) and type 2 (absorbed) AGN. We use several statistical analyses taking the upper-limits of thePAH lines into account utilizing survival analysis methods. The results of our $\log(L_{\rm 14-195keV})$ versus $\log(L_{\rm 3.3{\mu}m})$regression shows a positive correlation and the slope for the type 1/unobscured AGN is steeper than that of type 2/obscured AGN at a$3\sigma$ level. Also our analysis shows that the circum-nuclear SF is more enhanced in type 2/absorbed AGN than type1/un-absorbed AGN for low $L_{\rm 14-195keV}$ luminosity/low Eddington ratio AGN, while there is no significant dependence of SF activityon the AGN type in the high $L_{\rm 14-195keV}$ luminosities/Eddington ratios.

AN EXTENSION OF A RELIABLE WAVELENGTH COVERAGE OF THE AKARI NG GRISM MODE

Shunsuke Baba,TAKAO NAKAGAWA,NAIKI ISOBE,MAI SHIRAHATA,YOUICHI OHYAMA,KENICHI YANO,CHIHIRO KOCHI 한국천문학회 2017 天文學論叢 Vol.32 No.1

The Infrared Camera onboard the \textit{AKARI} satellite carried out spectroscopic observations with a grism mode named \textit{NG}, whose wavelength coverage was 2.5--5.0~$\mu$m. We reinvestigate the current flux calibration for the \textit{NG} grism mode, with which calculated flux density implausibly decreases at 4.9~$\mu$m especially for red objects due to the second-order light contamination. We perform a new spectral response calibration using blue and red standard objects simultaneously. New response curves which contain both the first- and second-order light are able to separate each contribution consistently and useful for studies of red objects such as CO ro-vibrational absorption in active galactic nuclei.

STUDY OF SPECTRAL ENERGY DISTRIBUTION OF GALAXIES WITH PRINCIPAL COMPONENT ANALYSIS

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

We performed Principle Component Analysis\,(PCA) over 264 galaxies in the {\it IRAS} Revised Bright Galaxy \blue{Sample \citep{Sanders2003}} using 12, 25, 60 and 100\,$\mu$m flux data observed by {\it IRAS} and 9, 18, 65, 90 and 140\,$\mu$m flux data observed by {\it AKARI}. We \blue{found} that (i)the first principle component \blue{was} largely contributed by infrared to visible flux ratio, (ii)the second principal component \blue{was} largely contributed by the flux ratio between {\it IRAS} and {\it AKARI}, (iii)the third principle component \blue{was} largely contributed by infrared colors.

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.

AKARI DEEP FIELD SOUTH: SPECTROSCOPIC OBSERVATIONS OF INFRARED SOURCES

Chris Sedgwick,STEPHEN SERJEANT,CHRIS PEARSON,Shuji Matsuura,MAI SHIRAHATA,Hideo Matsuhara,Lucia Marchetti,Glenn J. White,Mattia Vaccari,Ivano Baronchelli,Giulia Rodighiero,Bunyo Hadsukade,David L. Cl 한국천문학회 2017 天文學論叢 Vol.32 No.1

We present a summary of our spectroscopic redshift catalogue of 404 sources in the {\it AKARI} Deep Field South (ADF-S). We have used the AAOmega spectrograph to target mid-infrared and far-infrared sources selected primarily from {\it AKARI} observations in this field for which we were able to obtain optical counterparts. Our sources with identified redshifts include 316 with H$\alpha$ detections at z ≤ 0.345 and 15 sources at z > 1 with MgII or Lyα emission lines. About 13% of our z ≤0.345 sources are dominated by active galactic nuclei (AGN) emission, although many show emission from both star formation and AGNs. The median Balmer decrement is 5.9. Ultra-luminous infrared galaxies (ULIRGs) were found only in the higher-redshift sources. Optical and near infrared data will be available shortly, enabling calibration of the line luminosities and spectral energy distribution (SED) fitting for these sources.

New Spectral Evidence of an Unaccounted Component of the Near-infrared Extragalactic Background Light from the<i>CIBER</i>

Matsuura, Shuji,Arai, Toshiaki,Bock, James J.,Cooray, Asantha,Korngut, Phillip M.,Kim, Min Gyu,Lee, Hyung Mok,Lee, Dae Hee,Levenson, Louis R.,Matsumoto, Toshio,Onishi, Yosuke,Shirahata, Mai,Tsumura, K American Astronomical Society 2017 The Astrophysical journal Vol.839 No.1

<P>The extragalactic background light (EBL) captures the total integrated emission from stars and galaxies throughout the cosmic history. The amplitude of the near-infrared EBL from space absolute photometry observations has been controversial and depends strongly on the modeling and subtraction of the zodiacal light (ZL) foreground. We report the first measurement of the diffuse background spectrum at 0.8-1.7 mu m from the CIBER experiment. The observations were obtained with an absolute spectrometer over two flights in multiple sky fields to enable the subtraction of ZL, stars, terrestrial emission, and diffuse Galactic light. After subtracting foregrounds and accounting for systematic errors, we find the nominal EBL brightness, assuming the Kelsall ZL model, is 42.7(-10.6) (+11.9) nW m(-2) sr(-1) at 1.4 mu m. We also analyzed the data using the Wright ZL model, which results in a worse statistical fit to the data and an unphysical EBL, falling below the known background light from galaxies at. lambda<. 1.3 mu m. Using a model-independent analysis based on the minimum EBL brightness, we find an EBL brightness of 28.7(-3.3)(+5.1) nWm(-2) s(r-1) at 1.4 mu m. While the derived EBL amplitude strongly depends on the ZL model, we find that we cannot fit the spectral data to ZL, Galactic emission, and EBL from solely integrated galactic light from galaxy counts. The results require a new diffuse component, such as an additional foreground or an excess EBL with a redder spectrum than that of ZL.</P>