京都大学 / 新制・課程博士 / 博士(理学) / 甲第23013号 / 理博第4690号 / 新制||理||1672(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 太田 耕司, 教授 長田 哲也, 准教授 栗田 光樹夫 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Ram pressure stripping (RPS) can be described as the constant wind a galaxy experiences when moving through a galaxy cluster. It is well-established that galaxies undergoing this process lose substantial amounts of their atomic gas, but its effect on the cold molecular gas component is still not fully understood. Using high-resolution ALMA CO 2-1 data collected by the PHANGS and VERTICO surveys, I model the detailed effect of RPS in 36 Virgo galaxies on a 150 pc and 720 pc scale by calculating the ratio of ram pressure to the galaxy gravitational restoring force per unit area. If the ram pressure exceeds the restoring pressure, we assume the molecular gas parcel is susceptible to stripping. I reveal that roughly a quarter of our 36 galaxies are susceptible to molecular gas RPS, with up to 70% of their molecular gas in the outer disk (r > R50) being susceptible. As expected, low mass galaxies (log(M∗/M ) = 9.5) seem to be most affected. VERTICO galaxies show molecular gas susceptible to stripping at the outskirts and between their spiral arms. I also find higher fractions of RPS susceptible molecular gas in galaxies exhibiting clear atomic gas tails, suggesting that RPS impacts multiple gas phases at once. Finally, a phase space analysis suggests molecular gas RPS occurs primarily, potentially exclusively, at the first pericentric passage when ram pressure is maximal. / Thesis / Master of Science (MSc)

<p>The study of ongoing mergers is vital to understanding how intense star bursts are triggered, and how luminous infrared galaxies and ultra luminous infrared galaxies are formed. The Antennae (NGC 4038/39), at a distance of only 24.9 Mpc, represents the nearest example of a major merger between two gas rich spirals and provides us with a unique laboratory for studying molecular gas and star formation. I have obtained two fully sampled observations of the Antennae using the Herschel SPIRE Fourier Transform Spectrometer which I have supplemented with JCMT CO J = 3 − 2 observations. I detect CO, CI and NII emission throughout both the overlap region and the nucleus of NGC 4038. I measured the integrated intensity of the CO J = 4−3 to 8−7 and find that the overlap region is brighter for all but the J = 4 − 3 line. I find that, in the nucleus of NGC 4038, the CO spectral line energy distribution peaks at the 4−3 transition, while in the overlap region it peaks at the 3−2 transition. I modelled the CO emission using the non-local thermal equilibrium radiative transfer code RADEX coupled with a Bayesian likelihood code. I find a warm (Tkin > 600K) lower density (nH2 ∼ 200cm−3) component of molecular gas in the nucleus of NGC 4038, and similarly in the overlap region (Tkin > 600 K, nH2 ∼ 300cm−3) and find widespread evidence for multiple components of molecular gas throughout the system. These warm components in both regions correspond to ~ 1% of the total molecular gas. I find no evidence of x-ray dominated regions, cosmic rays or turbulent heating being the primary source of heating throughout the galaxy, while photodissociation regions or supernova and stellar winds may be the primary source of heating throughout the galaxy.</p> / Master of Science (MSc)

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<p>The barred spiral galaxy M83 (NGC5236) has been observed in the ¹²CO <i>J</i>=1–0 and <i>J</i>=2–1 millimetre lines with the Swedish-ESO Submillimetre Telescope (SEST). The sizes of the CO maps are 100×100, and they cover the entire optical disk. The CO emission is strongly peaked toward the nucleus. The molecular spiral arms are clearly resolved and can be traced for about 360º. The total molecular gas mass is comparable to the total Hi mass, but H₂dominates in the optical disk.</p><p>Iso-velocity maps show the signature of an inclined, rotating disk, but also the effects of streaming motions along the spiral arms. The dynamical mass is determined and compared to the gas mass. The pattern speed is determined from the residual velocity pattern, and the locations of various resonances are discussed. The molecular gas velocity dispersion is determined, and a trend of decreasing dispersion with increasing galactocentric radius is found.</p><p>A total gas (H₂+Hi+He) mass surface density map is presented, and compared to the critical density for star formation of an isothermal gaseous disk. The star formation rate (SFR) in the disk is estimated using data from various star formation tracers. The different SFR estimates agree well when corrections for extinctions, based on the total gas mass map, are made. The radial SFR distribution shows features that can be associated with kinematic resonances. We also find an increased star formation efficiency in the spiral arms. Different Schmidt laws are fitted to the data. The star formation properties of the nuclear region, based on high angular resolution HST data, are also discussed.</p>

Doctor of Philosophy / Department of Physics / Kristan L. Corwin / This research has focused on the development, demonstration, and characterization of a new type of laser based on optically-pumped gases contained within hollow optical fibers. These novel lasers are appealing for a variety of applications including frequency metrology in the mid-infrared, free-space communications and imaging, and defense applications. Furthermore, because of the hollow core fibers used, this technology may provide the means to surpass the theoretical limits of output power available from high power solid-core fiber laser systems. Gas-filled hollow-core fiber lasers based on population inversion from acetylene ([superscript]12C[subscript]2H[subscript]2) and hydrogen cyanide (HCN) gas contained within the core of a kagome-structured hollow-core photonic crystal fiber have now been demonstrated. The gases are optically pumped via first order rotational-vibrational overtones near 1.5 μm using 1-ns duration pulses from a home-built optical parametric amplifier. Narrow-band laser emission peaks in the 3-μm region corresponding to the ΔJ = ±1 dipole allowed rotational transitions between the pumped vibrational overtone modes and the fundamental C-H stretching modes have been observed in both molecules. High gain resulting from tight confinement of the pump and laser light together with the active gas permits these lasers to operate in a single pass configuration, without the use of any external resonator structure. Studies of the generated mid-infrared pulse energy, threshold energy, and slope efficiency as functions of the launched pump pulse energy and gas pressure have been performed and show an optimum condition where the maximum laser pulse energy is achieved for a given fiber length. The laser pulse shape and the laser-to-pump pulse delay have been observed to change with varying pump pulse energy and gas pressure, resulting from the necessary population inversion being created in the gases at a specific fiber length dependent on the launched pulse energy. Work is on going to demonstrate the first continuous wave version of the laser which may be used to produce a single coherent output from many mutually incoherent pump sources.

The barred spiral galaxy M83 (NGC5236) has been observed in the 12CO J=1–0 and J=2–1 millimetre lines with the Swedish-ESO Submillimetre Telescope (SEST). The sizes of the CO maps are 100×100, and they cover the entire optical disk. The CO emission is strongly peaked toward the nucleus. The molecular spiral arms are clearly resolved and can be traced for about 360º. The total molecular gas mass is comparable to the total Hi mass, but H2 dominates in the optical disk. Iso-velocity maps show the signature of an inclined, rotating disk, but also the effects of streaming motions along the spiral arms. The dynamical mass is determined and compared to the gas mass. The pattern speed is determined from the residual velocity pattern, and the locations of various resonances are discussed. The molecular gas velocity dispersion is determined, and a trend of decreasing dispersion with increasing galactocentric radius is found. A total gas (H2+Hi+He) mass surface density map is presented, and compared to the critical density for star formation of an isothermal gaseous disk. The star formation rate (SFR) in the disk is estimated using data from various star formation tracers. The different SFR estimates agree well when corrections for extinctions, based on the total gas mass map, are made. The radial SFR distribution shows features that can be associated with kinematic resonances. We also find an increased star formation efficiency in the spiral arms. Different Schmidt laws are fitted to the data. The star formation properties of the nuclear region, based on high angular resolution HST data, are also discussed.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17512号 / 工博第3671号 / 新制||工||1558(附属図書館) / 30278 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 青木 一生, 教授 稲室 隆二, 教授 斧 髙一 / 学位規則第4条第1項該当

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