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<p>I investigate the interstellar medium (ISM) of two nearby, resolved galaxies, M51 (NGC 5194) and Centaurus A (Cen A; NGC 5128) using spectroscopic and photometric data from the <em>Herschel Space Observatory</em> to search for local variations of the characteristics of the ISM. I find that the average characteristics of the ISM in Cen A, a giant elliptical galaxy, are similar to those typically found in normal star forming galaxies, despite its unique morphology and classification as a radio galaxy with an active galactic nucleus (AGN). Using <em>Herschel</em> photometry I find radial trends in the dust temperature, the dust mass, and unexpectedly, the gas-to-dust mass ratio. I hypothesise that the AGN is removing nearby dust grains via dust sputtering or expulsion via jets. A comparison of Herschel spectroscopy of important cooling lines to a photon dominated region (PDR) model reveals the strength of the far-ultraviolet radiation field, <em>G</em>₀, and the hydrogen gas density, <em>n</em>, in the PDR gas within Cen A are consistent with values found in other nearby galaxies. I do not observe any obvious radial trend in these characteristics and conclude that the high inclination of Cen A may be inhibiting the identification of any impact the AGN is having on the surrounding gas.</p> <p>An investigation of the gas in M51 using a similar spectroscopic dataset as with Cen A shows for the first time that a large fraction of the observed [C II](158 μm) emission in the centre of M51 originates in diffuse ionised gas. This fraction falls off with radius out to the arm and interarm regions. I also find via PDR modelling that there is a decreasing radial trend in the values of <em>G</em>₀ and <em>n</em>, and that in the arm and interarm regions they are the same. Thus, there appears to be no difference in the physical properties of the molecular clouds in the arm and interarm regions of the galaxy. The results of this thesis contribute to further understanding the characteristics of the ISM of nearby galaxies, as well as the evolution of the ISM in galaxies containing an AGN.</p> / Doctor of Philosophy (PhD)

Galaxy formation is a complex, nonlinear process that occurs over scales that span orders of magnitude in space and time. Of the many phenomena taking place within a galaxy, supernovae (SN) are among the most important. SN heat, stir, and eject gas from the galaxy. This has profound impact on the galaxy's evolution over cosmic time. Numerical simulations of galaxies must often include models for feedback from SN. We present a new model for SN feedback that captures the effects of previously ignored physics: thermal conduction. Massive stars form in clusters, allowing their SN ejecta to merge into a superbubble, which can vent from the disc to drive a high-entropy galactic outflow. Thermal conduction determines how much mass is mixed into this superbubble. We use this to study SN feedback in galaxy evolution, and come to four major conclusions. First, superbubbles drive stronger galactic outflows in compared to past models of SN feedback. Second, these outflows are key to both preventing the overproduction of stars and the formation of too-massive central bulges. High redshift outflows eject starforming gas, and preferentially remove bulge forming gas. Third, we show that SN cannot prevent runaway star formation in galaxies more massive than our own $(M_{halo}>10^{12}\;\rm{M_\odot})$. In these galaxies, SN are unable to prevent transport of gas towards the centre of the galaxy. These results suggest a transition between regulation from stars to regulation from supermassive black holes occurs at roughly this mass. Finally, we use our simulated galaxies to show recent observations of the Radial Acceleration Relation (RAR) are consistent with $\Lambda$CDM cosmology. The RAR ties galaxy kinematics to baryonic mass, in a tight, universal scaling relation. While this has been claimed as potential evidence of exotic new physics, we show this same tight relation occurs for galaxies formed in $\Lambda$CDM. / Thesis / Doctor of Philosophy (PhD)

Polarimetric CCD images of HII regions were obtained using a rotating polarizer device designed, built, and used in conjunction with the Spectral Line Imaging Camera (SLIC) at Virginia Tech's Martin Observatory in Giles County, Virginia. The SLIC uses a narrow bandpass interference filter coupled with a 58 mm camera lens and cryogenically cooled CCD camera to image diffuse, extended H-alpha emission over a 10° angular extent. A rotating polarizer device was placed in front of the H-alpha filter with images recorded at every 45° with respect to a fiducial setting. Stoke's parameters and were obtained and polarization maps of selected HII regions were created. Maps of the Monoceros supernova remnant and the Rosette Nebula (NGC 2237-9) were made in an attempt to detect polarization by selective extinction in H light. While this was not detected, polarization by scattering in a dust shell around the Rosette Nebula (NGC 2237-9) was observed. Scattered continuum light from the central star cluster NGC 2244 in the H-alpha bandpass was ruled out. Using Celnik's (1985) map of extinction across the Rosette Nebula at the H wavelength, coupled with Serkowski's empirical relationship between maximum polarization and color excess, it was shown that the maximum degree of polarization seen in the Rosette Nebula should be no more than 3% to 4%. The polarization observed in this project reaches values as high as 10%. It was found that a correlation exists between the H-alpha intensity and infrared emission by dust grains in all four IRAS waveband images in the suspected scattering region of the Rosette Nebula. A radial comparison between [SII] images and H-alpha images in the region of high polarization showed that the H-alpha intensity in that region is dominated by scattered H-alpha light from the Rosette Nebula. A single scattering model was constructed in an effort to predict the observed polarization. The model used parameters based on 21 cm observations by Kuchar and Bania (1993) of the HI shell which surrounds the HII region of the Rosette Nebula. The single scattering model can not accurately predict the degree of polarization. It was concluded that a multiple scattering model is required. A spatial comparison of the 12 m emission with the degree of polarization strongly suggested that multiple scattering is important in describing the observed radial behavior of polarization. Polarization images of regions in Cygnus were obtained. A polarization map of the North America Nebula (NGC 7000) and surroundings reveals a large amount of polarization. The map reveals that scattering of H-alpha light from the North America Nebula is the most likely cause of polarization in these images. From the analysis in this thesis, I conclude that in the northwest quadrant, at radial distances greater than 40 from the center of the Rosette Nebula, the observed H-alpha intensity is due to scattered H light from the nebula itself. This implies that, in H-alpha , the Rosette Nebula appears slightly larger than it actually is. With evidence of polarization by scattered H supported by the polarization map of the North America Nebula (NGC 7000), it is concluded that other HII regions may very well appear larger in H-alpha than they actually are. Thus, scattered H-alpha light may account for a small part of the more extended warm ionized medium as well. / Ph. D.

Os cianopoliinos (HCnN, n = 1, 3, 5, ...) e seus isômeros, os isocianopoliinos (HCn-1NC), constituem duas famílias de moléculas já identificadas no meio interestelar. No intuito de auxiliar a detecção e investigar a formação destas moléculas neste ambiente, foram obtidas as geometrias, as constantes rotacionais, os momentos de dipolo, as frequências vibracionais e as intensidades fundamentais de infravermelho em níveis MP2/cc-pVTZ (n = 1 a 17), CCSD/cc-pVDZ (n = 1 a 13) e CCSD/cc-pVTZ (n = 1 a 7). Além disso, foi empregado o modelo de partição em carga - fluxo de carga - fluxo de dipolo, CFCFD, em termos dos multipolos atômicos advindos da Teoria Quântica de Átomos em Moléculas, QTAIM, para compreender os efeitos do tamanho da cadeia sobre as propriedades elétricas destas moléculas, como suas intensidades de infravermelho. Os resultados indicam que o nível CCSD/cc-pVTZ é o que melhor descreve as propriedades mencionadas para os menores cianopoliinos e isocianopoliinos. Contudo, devido à demanda computacional, é preciso optar entre os níveis MP2/cc-pVTZ e CCSD/cc-pVDZ para abordar espécies maiores. Assim, os momentos de dipolo destes maiores cianopoliinos são mais bem descritos pelo nível MP2/cc-pVTZ, enquanto CCSD/cc-pVDZ é mais indicado para tal propriedade em respectivos isocianopoliinos. Por sua vez, as intensidades de infravermelho destas famílias apresentam melhor concordância com dados experimentais quando determinadas em nível CCSD/cc-pVDZ. Além disso, tanto para cianopoliinos quanto para isocianopoliinos, o aumento do tamanho das cadeias resulta num incremento das intensidades do estiramento CH, o que é explicado por variações no fluxo de carga eletrônica. O estiramento das ligações triplas CC centrais é o modo mais intenso em grandes cianopoliinos, o que também se deve ao fluxo de carga observado. Ademais, o espectro dos isocianopoliinos apresenta um número maior de bandas relevantes na região de estiramento de ligações triplas CC. Um estudo também foi conduzido, onde foram estimados os dados termodinâmicos, as geometrias do estado de transição e as constantes de velocidade da reação HCnN &rarr; HCn-1NC (n = 1 a 9) para temperaturas entre 298,15 e 3000 K. Os níveis B3LYP/aug-cc-pVsZ, MPW1K/aug-cc-pVsZ (s = Q) e CCSD(T)/aug-cc-pVmZ (m = T e Q) foram adotados em um tratamento composto para as reações com n = 1, 3 e 5, enquanto as reações com n = 7 e 9 foram investigadas de forma semelhante, porém com s = T e m = D e T. O método B3LYP foi o que apresentou melhor desempenho comparado ao MPW1K na determinação de frequências e geometrias. Os resultados indicam que esta reação é exotérmica no sentido em que os cianopoliinos são formados e, portanto, é mais fácil de ocorrer em ambientes mais frios do meio interestelar. Por outro lado, suas constantes de velocidade no sentido direto e inverso tendem a ser de mesma magnitude em temperaturas elevadas, indicando que estes ambientes mais quentes são mais propícios para detecção de isocianopoliinos. Por fim, equações parametrizadas foram ajustadas para reproduzir nossos dados de constantes de velocidade das reações com n = 1 até 9 dentro do intervalo de temperaturas considerado. / Cyanopolyynes (HCnN, n = 1, 3, 5, ...) and their isomers, isocyanopolyynes (HCn-1NC), constitute two families of molecules already identified in the interstellar medium. In order to provide data for their detection and to investigate the formation of these molecules in this environment, geometries, rotational constants, dipole moments, vibrational frequencies and infrared fundamental intensities were obtained at MP2/cc-pVTZ (n = 1 to 17), CCSD/cc-pVDZ (n = 1 to 13) and CCSD/cc-pVTZ (n = 1 to 7) levels. Furthermore, the partition model in charge - charge flux - dipole flux, CFCFD, from atomic multipoles given by the Quantum Theory of Atoms in Molecules, QTAIM, was applied to understand the effects of chain size on electrical properties of these molecules, such as intensities. Results indicate that the best description of the properties mentioned is achieved at the CCSD/cc-pVTZ level for smaller cyanopolyynes and isocyanopolyynes. However, due to computational demand, one needs to choose between MP2/cc-pVTZ and CCSD/cc-pVDZ levels to deal with larger species. In this sense, the dipole moments of large cyanopolyynes are better described by the MP2/cc-pVTZ level, while CCSD/cc-pVDZ is indicated for such property in respective isocyanopolyynes. In addition, the infrared intensities of both families from CCSD/cc-pVDZ calculations are in better accordance with experimental data. Moreover, chain size increases of cyanopolyynes and isocyanopolyynes result in intensity increments of CH stretching, which is explained by electronic charge flux changes. The stretching of central CC triple bonds is the strongest mode for large cyanopolyynes and this is also due to charge flux. A study was also conducted, in which thermodynamic data, transition state geometries and rate constants of the reaction HCnN &rarr; HCn-1NC (n = 1 to 9) were estimated for temperatures between 298.15 and 3000 K. B3LYP/aug-cc-pVsZ, MPW1K/aug-cc-pVsZ (s = Q) and CCSD(T)/aug-cc-pVmZ (m = T and Q) were adopted in a combined treatment for reactions with n = 1, 3 and 5, while reactions with n = 7 and 9 were investigated in a similar way, but with s = T and m = D and T. Frequencies and geometry data from the B3LYP method exhibited a better performance than MPW1K. The results indicated that this reaction is exothermic in the direction that leads to cyanopolyynes, and therefore it is easier to occur in colder environments of the interstellar medium. On the other hand, rate constants of forward and reverse reactions tend to show the same magnitude at higher temperatures, indicating these warmer environments are more amenable to detection of isocyanopolyynes. Finally, parameterized equations were fitted to reproduce our rate constant data for reactions with n = 1 to 9 in the temperature range considered.

Des nuages moléculaires aux étoiles, l'ensemble des stades d'évolution des étoiles jeunes peuvent être observés dans le domaine submillimétrique. A cette fin, le télescope Herschel a observé, dans le cadre d'un relevé de la Ceinture de Gould, plusieurs nuages moléculaires. Lorsque ces nuages se fragmentent, des coeurs denses, accumulant de la poussière et du gaz, se forment et se contractent. Nous avons effectué un relevé exhaustif des coeurs denses préstellaires dans le nuage moléculaire d'Ophiuchus qui apparaissent couplés avec des structures filamentaires dans le cadre du paradigme de la formation d'étoiles au sein de filaments interstellaires. La région n'était pas connue pour être filamentaire, malgré des alignements de protoétoiles observables. Ce nuage moléculaire présente la particularité d'être soumis à une rétroaction importante venant d'étoiles actives à proximité, visible dans la structure du nuage moléculaire. Oph B-11, mise en évidence par des observations interférométriques, est un précurseur de naine brune, de masse finale trop faible pour que l'étoile produite brûle de l'hydrogène. Leur mécanisme de formation est mal connu. Il faut caractériser et observer un premier candidat pré-naine brune. Oph B-11 a été détectée à proximité d'un choc proche, que nous avons caractérisé chimiquement. De plus, à plus haute résolution avec ALMA, nous avons montré l'environnement moléculaire structuré, contraint le mécanisme de formation de ce type d'objet. Ces observations dévoilent une série de chocs dans plusieurs traceurs, coïncidant avec la détection de la pré-naine brune, favorisant le scénario gravo-turbulent pour la formation des naines brunes. / From molecular clouds to stars, every step of the evolution of young stars can be observed in the submillimetric range. The Herschel Space Telescope observed, as part of the Herschel Gould Belt Survey, many molecular clouds.When these molecular clouds are fragmenting, dense prestellar cores accumulating dust and gaz are forming and contracting. We performed a census of prestellar dense cores in the Ophiuchus Molecular Cloud, which appear to be coupled with filamentary structures, as part of the paradigm of star-formation inside insterstellar filaments. The region was not previously known as filamentary, despite the observation of protostellar alignments.This molecular could is under the heavy feedback of active stars nearby seen in the structure of the molecular cloud.Oph B-11, detected with interferometric observations, is a brown dwarf precursor, which final mass will not be important enough for the final star to burn hydrogen. Their formation mechanism is not well constrained, we must find and characterize a first candidate pre-brown dwarf.Oph B-11 was detected along a nearby shock, we characterize chemically. Moreover, higher resolution studies with ALMA show a structured molecular environment, and help us constrain the mechanism of formation of this kind of objects. These observations show a series of shocks in differents tracers, spatially coincident with the detected position of the pre-brown dwarf, in favor of the gravo-turbulent scenario for the formation of brown dwarfs.

Les galaxies massives sont moins nombreuses que ce qui est attendu avec le modèle standard (le modèle Λ-CDM). Ceci ce traduit par une formation d’étoiles moins importante que prévue dans les galaxies. Pour expliquer celà, il est globalement accepté que des processus stoppent le formation d’étoiles. Pour les galaxies massives, ceci est expliqué par l’action des trous noirs supermassifs. En accrétant du gaz, le trou noir central produit de l’énergie et de l’impulsion. Quand l’accrétion devient importante, le trou noir forme un noyau actif de galaxie, et l’énergie peut ralentir la formation d’étoiles, par chauffage du gaz, de la turbulence, ou par ablation du gaz (feedback négatif). Cependant, il existe des cas de feedback positif qui favorise la formation d’étoiles en comprimant le gaz. En particulier, une partie des noyaux actifs produisent des jets de plasma qui sont observés en émission radio. Ces jets radio peuvent intéragir avec du gaz le long de leur direction de propagation. Des telles interactions sont susceptibles de déclencher de la formation d’étoiles (formation induite par les jets). Ma thèse porte sur les interactions jet-gaz dans des radio galaxies proches. J’ai étudié l’effet du jet sur l’efficacité de la formation d’étoiles pour des interactions à des échelles globales (quelques kiloparsecs) et intermédiaires (quelques centaines de parsecs). Pour celà, j’ai observé et cartographié le gaz moléculaire, qui est un élément clé de la formation d’étoiles. Cette phase froide est observable grâce aux équipements au sol actuels de radio astronomie, comme ALMA, APEX, NOEMA et le 30m de l’IRAM. / Massive galaxies are less abundant than predicted by the standard model of galaxy formation (the Λ-CDM model). This means that galaxies form less stars than expected. To explain this behaviour, it is commonly accepted that some processes are at play and quench star formation. For massive galaxies, it is explained by the feedback of the supermassive black holes. While accreting gas, the central black hole produces energy and momentum. When gas accretion becomes important, the black hole forms an active galactic nucleus, and the energy is expected to quench star formation, via gas heating, turbulence or gas removal (negative feedback). However, evidence is found of so-called AGN positive feedback that favours star formation by compressing the gas. In particular, a fraction of the AGN population produces jets of plasma that are observed in radio emission. These radio jets may interact with gas that is located along the direction of propagation. Such interactions are invoked to trigger star formation (jet-induced star formation). My PhD focused on the jet-gas interaction for nearby radio galaxies. I explored the effect of the jet on the star formation efficiency in such interactions at global (few kiloparsecs) and intermediate (few hundreds parsecs) scales. To do so, I searched and mapped the molecular gas (via CO emission lines) that is a key ingredient for star formation. This cold gas is observable using current radio astronomy ground-based facilities, like ALMA, APEX, NOEMA and the 30m telescope.

Utilizing data from the Kepler Mission, we analyze a flickering phenomenon in the symbiotic variable star CH Cygni. We perform a spline interpolation of an averaged lightcurve and subtract the spline to acquire residual data. This allows us to analyze the deviations that are not caused by the Red Giant’s semi-regular periodic variations. We then histogram the residuals and perform moment calculations for variance, skewness, and kurtosis for the purpose of determining the nature of the flickering. Our analysis has shown that we see a much smaller scale flickering than observed in the previous literature. Our flickering scale is on the scale of fractions of a percent of the luminosity. Also, from our analysis, we are very confident that the flickering is a product of the accretion disc of the White Dwarf.

Over the past two decades, much has been learned about the atmospheric structure of the pulsating Mira-type variable stars from computer modeling and the analysis of ultraviolet and visible wavelength spectra. This talk reports on the first set of infrared spectra taken of these stars under high dispersion with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. A sample of 25 galactic Miras was observed in the 10-37 micron spectral regime anywhere from two to several times during their pulsation cycle. Many of the stars observed show marked changes in overall flux levels as a function of phase. We are able to identify many strong emission lines from neutral and singly ionized metals and emission features due to silicate and carbon dusts and molecular constituents. This work was financially supported through a NASA Spitzer grant for Program GO 50717.