京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20919号 / 理博第4371号 / 新制||理||1627(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 嶺重 慎, 准教授 前田 啓一, 教授 太田 耕司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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京都大学 / 新制・課程博士 / 博士(理学) / 甲第24412号 / 理博第4911号 / 新制||理||1702(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 橋本 幸士, 准教授 福間 將文, 教授 杉本 茂樹 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24417号 / 理博第4916号 / 新制||理||1702(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 嶺重 慎, 教授 前田 啓一, 教授 太田 耕司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The first detection of a gravitational wave (GW) enabled our observation of the Universe through a revolutionary messenger and unveiled phenomena that are occurring in a range of very strong gravitational fields and relativistic velocities. These physical regimes, previously inaccessible to humankind, can now be studied. In particular, the discoveries of an unexpected population of stellar-mass binary black holes (BBH), and unexpected masses for binary neutron star (BNS) components have both pointed to new astrophysics, and to unprecedented tests of the general relativity theory. This thesis focuses on the development of a new method of gravitational wave data analysis, aiming to investigate weak features in the proximity to well-identified BBH merger signals. The method is based on a dedicated version of coherentWaveBurst (cWB), an unmodelled gravitational waves transient search algorithm, developed in the LIGO Scientific Collaboration (LSC) and Virgo Collaboration and widely used on LIGO-Virgo-KAGRA (LVK) data. CoherentWaveBurst relies on the coherent detection of an excess of energy inside the combined data of all the gravitational waves detectors inside the detectors network. Such excess of energy must pass several internal thresholds of the pipeline to be accepted as a possible gravitational wave candidate and these thresholds evaluate not only the strength of the signal with respect to the background noise but also how balanced is the energy distribution among the detectors of the network, its coherence, as well as other quantities whose purpose is to rule out possible outliers due to the presence of non-stationary noise. To develop such a method, it was decided to adopt as science case the search for echoes. In literature, it has been proposed that the gravitational radiation generated from a binary compact objects (CBCs) coalescence might display exotic characteristics if compared to the predicted one generated by black hole-black hole (BH-BH), neutron star-neutron star (NS-NS), or neutron star-black hole (NS-BH) binaries which are, for now, the only detected emitters of gravitational waves. Such differences arise from the proposal that the involved compact objects (COs) of the binary are not standard black holes but instead black hole mimickers called exotic compact objects (ECOs). If this is the case the gravitational wave signal generated from such a binary would display repeated gravitational wave pulses, of widely uncertain morphology, after the merger-ringdown phase of the gravitational signal. These repeated gravitational wave pulses are called echoes, one class of low energetic signals whose presence inside gravitational wave data, this new algorithm is searching for. The proposed data analysis methodology searching for echoes is agnostic over the properties of the predicted gravitational wave pulses emitted by an ECO binary. Indeed, the variety of theoretical alternatives to black holes is not converging over a well-defined post-merger-ringdown signal, each model has its own properties and characteristic features. Therefore, the possibility to investigate the morphological features of possible outliers in the post-merger phase of detected GW signals is fundamental in the process of inferring their nature. Having their morphology recovered without priors makes the proposed search more general than the variety of theoretical models of echoes. This procedure is tested over real data from past LIGO-Virgo observing runs (O1, O2, and O3), and the capability of the search in estimating the main morphological parameters of echoes, such as their arrival time, mean frequency, as well as the amplitude attenuation between subsequent pulses, is investigated. This work concludes that the current state-of-the-art methods and detectors find no evidence for echoes of any morphologies. Such a study extended to lower signal-to-noise ratio (SNR) the detectability of echoes associated with the public gravitational-wave transient catalog of BBH mergers released by the LIGO and Virgo Collaboration. It also sets best quantitative upper limits on the amplitude of low energy signals occurring after the merger-ringdown. To achieve these results, new post-processing tools are developed and optimised to detect and characterize possible energy excess inside a user-defined time window. This required the development of the code and to adapt the cWB infrastructure to the new working requirements which also involves a re-tuning of cWB itself. The optimization of the performances is based on off-source simulations for assessing the detection efficiency and false alarm probability of signal candidates.

This is an exciting time for Gravitational Wave (GW) theory and observations. From a theoretical standpoint, the grand-challenge problem of the full evolution of a Binary Black Hole (BBH) system has been solved numerically, and a variety of source simulations are made available steadfastly. On the observational side, the first generation of state-of-the-art GW detectors, LIGO and Virgo, have achieved their design goal, collected data and provided astrophysically meaningful limits. The second generation of detectors are expected to start running by 2015. Inspired by this zeitgeist, this thesis focuses on the detection of potential GW signatures from the coalescence of BBH in ground-based laser interferometers. The LIGO Scientific Collaboration has implemented different algorithms to search for transient GW signatures, targeting different portions of the BBH coalescence waveform. This thesis has used the existing algorithms to study the detection potential of GW from colliding BBH in LIGO in a wide range of source parameters, such as mass and spin of the black holes, using a sample of data from the last two months of the S5 LIGO science run (14 Aug 2007 to 30 Sept 2007). This thesis also uses numerical relativity waveforms made available via the Numerical INJection Analysis project (NINJA). Methods such as the Chirplet based analysis and the use of multivariate classifiers to optimize burst search algorithms have been introduced in this thesis. These performance studies over a wide parameter space were designed to optimize the discovery potential of ground-based GW detectors and defining strategies for the search of BBH signatures in advanced LIGO data, as a step towards the realization of GW astronomy

I present spectroscopic measurements for 260 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample of Sloan Digital Sky Survey (SDSS) quasars at 1.5 < z < 3.5. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C IV λ1549, Mg II λλ2798, 2803, Hβ λ4861, and [O III] λλ4959, 5007 emission lines, in each source. The spectral inventory is utilized primarily to develop prescriptions for obtaining more accurate and precise redshifts, black hole masses, and accretion rates for all quasars. Additionally, the measurements facilitate an understanding of the dependence of rest-frame ultraviolet–optical spectral properties of quasars on redshift, luminosity, and Eddington ratio, and test whether the physical properties of the quasar central engine evolve over cosmic time.

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<p dir="ltr">The Black Hole Illusion (BHI) is a nighttime aviation landing illusion where pilots overestimate their descent angle. The BHI occurs when only the outline of the runway is visible to pilots, usually at night with little illumination of the environment. This illusion is dangerous, as it causes pilots to perceive themselves at a high descent angle; and they compensate by flying lower, resulting in a possible crash into the ground or obstacles before the runway. A common interpretation of the BHI is that it represents a perceptual illusion, where the descent angle is misperceived. We quantitatively analyzed two different perceptual theories that predict pilots perceived descent angle during the BHI experience; and we also quantitatively analyzed another perceptual theory to apply during nighttime approaches to alleviate the disorientation experienced from the BHI. Of the first two theories, Perrone's algorithm (Perrone, 1983) predicts that the magnitude of the illusion should vary with runway width/length in nighttime conditions, compared to no illusion and no effect of runway width/length in daylight conditions. On the other hand, the eye-level algorithm (adapted from the work in Galanis, Jennings, and Beckett (1998) and Robinson, Williams, and Biggs (2020)) predicts that there should be no effect of runway width/length in either nighttime or daylight conditions. The last algorithm, the focus of expansion algorithm (adapted from the theory of Gibson (1950) and Gibson (1966)), details a way that pilots can obtain the landing position of their aircraft without estimating their angle of descent, thereby alleviating possible disorientation experienced during nighttime approaches. Additionally, we conducted three empirical studies: The first two aimed at testing Perrone's algorithm and the eye-level algorithm; and the third aimed at testing the focus of expansion algorithm. Across the first two empirical studies, we did demonstrate a BHI for the nighttime evaluations of descent angle; but the data did not support either algorithm. In the third empirical study, the data did not support the focus of expansion algorithm; however, we found that participants were more accurate with estimating the aircraft's landing position when the landing position was closer to the beginning of the runway. Overall, we conclude that the BHI may reflect general disorientation in conditions with limited information.</p>