Takao Nakagawa

第1回観測ロケットシンポジウム（2018年7月17日-18日. 宇宙航空研究開発機構宇宙科学研究所（JAXA)(ISAS)）, 相模原市, 神奈川県著者人数: 16名ほか資料番号: SA6000127021レポート番号: Ⅵ-2

The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, JapanWe made systematic observations of the HI Br alpha (4.05 micrometers) and Br beta (2.63 micrometers) lines in 52 nearby (z less than 0.3) ULIRGs with AKARI. Our observations show that ULIRGs have a tendency to indicate higher Br beta/Br alpha line ratios than those observed in Galactic HII regions, and three galaxies in the observed sample show the anomaly of the Br beta/Br alpha line ratios (in the order of 1.0), which are significantly higher than that of case B (0.565). The high Br beta/Br alpha line ratios cannot be explained by the combination of the dust extinction and the case B, since dust extinction reduces the ratio. We simulate HII regions in the ULIRGs with the Cloudy code, and show that the high Br beta/Br alpha line ratios can be explained with the combination of the optically thick Br alpha line and the optically thin Br beta line. To achieve the column density large enough to make the Br alpha line optically thick, the gas density is required as high as n in the order of 10(exp 8) cm(exp -3). Hence our results suggest that star-formation activity in ULIRGs occurs preferentially in high-density clouds.Physical characteristics: Original contains color illustrations

The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, JapanWe aim to study star-forming galaxies by using a blind spectroscopic survey at mid-infrared (MIR) wavelengths to understand evolution of their star formation rate (SFR) and specific SFR (SFR per stellar mass) up to z in the order of 0.5, by paying particular attention to their Polycyclic Aromatic Hydrocarbon (PAH) properties. We conducted a low-resolution (R approximately equal to 50) slitless spectroscopic survey at 5-13 micrometers of 9 micrometers flux-selected sources (approximately greater than 0.3 mJy) around the North Ecliptic Pole with the Infrared Camera (IRC) onboard AKARI. We identified 48 PAH galaxies with PAH 6.2, 7.7, and 8.6 micrometers features at z approximately less than 0.5. The rest-frame optical-MIR spectral energy distributions (SEDs) based on CFHT and AKARI/IRC imaging are produced and analyzed in conjunction with the PAH spectroscopy. The rest-frame SEDs of all PAH galaxies have a universal shape with stellar and 7.7 micrometers (PAH) bumps, except that the PAH enhancement (luminosity ratio of the 7.7 micrometers PAH feature over the 3.5 micrometers stellar bump) significantly varies as a function of the PAH luminosities. We identified a PAH-enhanced population at z approximately less than 0.35, whose SEDs and luminosities are typical of luminous infrared galaxies. They show particularly larger PAH enhancement at high luminosity, implying that they are vigorous star-forming galaxies with elevated specific SFR. Our composite starburst model that combines a young and dusty starburst with a very old population can successfully reproduce most SED characteristics.Number of authors: 27Physical characteristics: Original contains color illustrations

The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, JapanWe observed near-infrared (NIR) absorption bands in 48 ultraluminous infrared galaxies (ULIRGs) to study physical conditions in star-forming regions. We focus on two absorption features in this study: the H2O ice absorption at 3.0 micrometers, which traces dark clouds (A(sub V) greater than a few mag), and the aliphatic carbon absorption at 3.4 micrometers, which traces diffuse clouds (A(sub V) less than 1 mag). Spectral analysis shows that optical depths of H2O ice and aliphatic carbon in most of the ULIRGs are similar to those in diffuse clouds in the Galaxy when normalized by silicate optical depth, and ULIRGs do NOT consist of dark clouds. This suggests that the star-forming regions in ULIRGs have more intense radiation field than typical dark clouds in the Galaxy. We also examined the profile of H2O ice for objects showing relatively deep absorption. The observed profiles of H2O ice in ULIRGs sometimes show a sign of saturated absorption, while the continuum emission is not completely absorbed by the feature. This suggests that the dark clouds, where H2O ice resides, do not cover the background sources entirely. These results imply that the dark clouds are sparsely distributed in ULIRGs.Physical characteristics: Original contains color illustrations

The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, JapanThe far-infrared excess of stars with protoplanetary disks and debris disks is expected to provide us with key information on dust dissipation process in the outer disks. In order to reveal the typical behavior of the disks including objects fainter than the current survey limit, we stacked far-infrared images cut out from the image of AKARI all-sky survey in the 90 micrometers band (WIDE-S) on the basis of known object positions. We carried out two type of studies: one is the study on protoplanetary disks based on observations of T Tauri stars, and the other is the study on debris disks based on observations of A-type main sequence stars. Our studies show that, as disks evolve from protoplanetary disks to debris disks, the dust dissipation timescale becomes longer. This suggests that with disk evolution the dominant dust component changes from primordial dust, which remains small without growing into planetesimals, to secondary dust, which is formed by collisional destruction of planetesimals.Physical characteristics: Original contains color illustrations

The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, JapanWe analyzed the 4.67 micrometers CO ro-vibrational absorption band in nearby ten active galactic nuclei (AGNs) observed with AKARI and Spitzer by fitting a plane-parallel local thermal equilibrium gas model. We found that the CO gas is warm (200-500 K) with a large column density (N(sub H) less than in the order of 10(exp 23) cm-2). Such a large column of warm gas is not achievable with UV heating or shock heating in starbursts. The most convincing heating source is X-ray photons emitted from the nuclei, which can produce warm gas of N(sub H) in the order of 10(exp 24) cm-2. This indicates that the region probed by the CO absorption is in the vicinity of the nuclei. The hydrogen column density estimated from the CO band is smaller than that inferred from X-ray observations. The observed deep absorption implies that the gas is close to the continuum source. We suggest that the probed region is outside the X-ray emitting region and just in front of the dust sublimation layer, which can be designated as the inner rim of the obscuring material around the AGNs.Physical characteristics: Original contains color illustrations

The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, JapanWe present our continuous efforts over the last decade - since the launch of AKARI - to unveil the environmental impacts on dust properties of galaxies in the local and distant universe by making full use of the AKARI 'all-sky' and 'pointed' observations. We first introduce our new result on the environmental effects on the dust temperature (T(sub dust)) of local star-forming galaxies. By performing stacking analysis of the AKARI FIS all-sky map (at the positions of SDSS star-forming galaxies in different environments), we find that T(sub dust) of galaxies increases with increasing environmental density, supporting a cold dust stripping scenario in high-density environments. We also present the results from our systematic, wide-field MIR 'pointed' observations of distant clusters with AKARI/IRC, in combination with our Subaru H alpha observing campaign. Taking advantage of the wide-field coverage of AKARI (and Subaru), we revealed that dust-obscured galaxies are most frequently triggered at the periphery of distant clusters. The coincidence of the environment of dusty galaxies and that of galaxy color transition suggests a strong link between dusty galaxies and the process of environmental quenching during the course of cluster-scale assembly.Physical characteristics: Original contains color illustrations

SPICA Science Conference from Exoplanets to Distant Galaxies: SPICA's New Window on the Cool Universe (June 18-21, 2013. Ito Hall, the University of Tokyo), Bunkyou-ku, Tokyo, JapanFor optical testing of the SPICA telescope, we require sub-aperture stitching interferometry, because an accurate autocollimating flat mirror (ACF) with a size comparable to the telescope (3.2 m) is hardly available. Therefore we use small ACFs which rotate with respect to the optical axis of the telescope to cover the full pupil of the telescope. We verified the feasibility of the sub-aperture stitching interferometry by performing real optical measurement. At cryogenic temperatures, in particular, ACFs can be deformed due to thermal contraction. Since surface figure errors of ACFs can make errors in the sub-aperture stitching result, we propose a new method to mitigate the effects of the ACF errors. We evaluated the feasibility of this method by performing an experimental study utilizing the 800-mm telescope and a 300-mm ACF with a designed large deformation. As a result, we find that this method is applicable for the optical test of the telescope, although it needs to be further developed.Physical characteristics: Original contains color illustrations

SPICA Science Conference from Exoplanets to Distant Galaxies: SPICA's New Window on the Cool Universe (June 18-21, 2013. Ito Hall, the University of Tokyo), Bunkyou-ku, Tokyo, JapanSPICA Coronagraph Instrument (SCI) is an instrument dedicated for direct detection and characterization of exoplanets and also for other science that needs a high-contrast imaging and spectroscopic capability in the near to mid-infrared wavelengths. We will present the major science cases for exoplanets from the instrument proposal of SCI. Thanks to the high-contrast imaging and spectroscopic capability, we will be able to tackle the various problems on the exoplanet science. SCI will give us the unique opportunity to observationally understand the formation process of Jovian planets, which is still poorly understood, by measuring temperatures of young Jovian planets. Spectroscopy of planet atmospheres will enable us to reveal the chemical compositions by measuring the abundances of various important molecules such as CO, CH4, NH3, H2O, H2 etc. We will also access to the structure of Jovian atmosphere, for example the existence of thermal inversion which is known for our Solar system planets. Furthermore, the direct detection of icy giants around early-type stars with SCI will open a new window to investigate these enigmatic planets.The clerical error of an author's name: T. KOMATSUNumber of authors: 57Physical characteristics: Original contains color illustrations

SPICA Science Conference from Exoplanets to Distant Galaxies: SPICA's New Window on the Cool Universe (June 18-21, 2013. Ito Hall, the University of Tokyo), Bunkyou-ku, Tokyo, JapanThe time domain remains, in many respects, the least explored of parameter spaces in astronomical studies. The purpose of this article is to encourage the SPICA community to consider the potential of rapid infrared timing observations. The specific example considered is that of variable emission from relativistic jets in compact accreting objects, whose formation and powering mechanisms we still do not understand. Infrared observations have the potential to give us fundamental insight on the conditions required for jet formation in accreting stellar-mass black holes. This is because particle acceleration is thought to be magnetically-driven, and the spectral transition between optically-thin and self-absorbed jet synchrotron radiation lies in the infrared. We review recent observations from WISE showing that we have the capability to measure key physical parameters of the jet, and their time-dependence on rapidly-changing conditions in the accretion flow around the black hole (on timescales of just a few seconds). SPICA will provide a breakthrough in this field because of its sensitivity and broadband coverage, and we detail an example SPICA observation on short (tens of milliseconds) timescales. We believe that SPICA has the potential to make great impact on time domain science, and we discuss some technical requirements that will enable this.Physical characteristics: Original contains color illustrations

SPICA Science Conference from Exoplanets to Distant Galaxies: SPICA's New Window on the Cool Universe (June 18-21, 2013. Ito Hall, the University of Tokyo), Bunkyou-ku, Tokyo, JapanWe carried out systematic observations of the HI recombination line Bra (4.05 μm) in nearby (z less than 0.3) ultraluminous infrared galaxies (ULIRGs), using AKARI near-infrared 2.5-5.0 μm spectroscopy. We derived star formation rates (SFRs) from the Bra line, whose observed flux is predicted to be the highest among HI recombination lines in conditions with large dust extinction (visual extinction Av greater than 15 mag) expected in ULIRGs. Using the 3.3 μm polycyclic aromatic hydrocarbon emission in addition to the Bra line as an indicator of the SFR, we estimated the contribution of the star formation to the total infrared luminosity in 51 ULIRGs. The contribution was on average 28 plus or minus4 0/o in ULIRGs optically classified as H II, while 14 plus or minus2 0/o in ULIRGs optically classified as LINER or Seyfert. This result indicates that the star formation is significantly active in H II ULIRGs and other energy source, i.e. active galactic nuclei, is needed in LINER ULIRGs.Physical characteristics: Original contains color illustrations

SPICA Science Conference from Exoplanets to Distant Galaxies: SPICA's New Window on the Cool Universe (June 18-21, 2013. Ito Hall, the University of Tokyo), Bunkyou-ku, Tokyo, JapanWe 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+AO188. The detected CO absorption lines up to highly excited rotational levels reveal that hot dense molecular clouds exist around the AGN under the extreme physical conditions.Physical characteristics: Original contains color illustrations

We produce a catalogue of polycyclic aromatic hydrocarbon (PAH) 3.3 $\mu$m, Br$\alpha$ and infrared luminosity ($L$(IR)) of 412 local galaxies, and investigate a relation between these physical parameters. We measure the PAH 3.3 $\mu$m and Br$\alpha$ flux using AKARI 2-5 $\mu$m spectra and the $L$(IR) using the AKARI-all-sky-survey data. The $L$(IR) and redshift ranges of our sample are $L$(IR)=$10^{9.7-12.8}$L$_\odot$ and $z_{\rm spec}=0.002-0.3$, respectively. We found that the ratio of $L$(PAH 3.3 $\mu$m) to $L$(IR) is constant at $L$(IR) $<$ $10^{11} \rm L_\odot$ whereas it decreases with the $L$(IR) at higher $L$(IR). Also, the ratio of $L$(Br$\alpha$) to $L$(IR) decreases with the $L$(IR). The both $L$(PAH)/$L$(IR) and $L$(Br$\alpha$)/$L$(IR) ratios are not strongly dependent on galaxy type and dust temperature. The relative weakness of the two ratios could be attributed to destruction of PAH, a lack of UV photons exciting PAH molecules or ionising hydrogen gas, extremely high dust attenuation, or active galactic nucleus contribution to the $L$(IR). Although we cannot determine the cause of the decreases of the luminosity ratios, a clear correlation between them implies that they are related with each other. The catalogue presented in our work will be available at the AKARI archive web page.