Rozprawy doktorskie na temat „Galactic Outflow”

Active galactic nuclei (AGN) ubiquitously show outflows. It is now widely recognized that these outflows are key components in the evolution of super-massive black holes and their host galaxies. As important as these outflows are, we still lack sufficient understanding of their structure and energetics. The majority of the work presented in this thesis involved photoionization modeling of AGN outflows along with analysis of density diagnostics in order to determine the distances and energetics of observed outflows. The main findings of these analyses are that 1) outflows are often at distances of hundreds to thousands of parsecs from the central supermassive black hole and 2) quasars outflows can be sufficiently powerful to provide feedback in galactic evolution scenarios. We also find in some cases that the recombination timescales of metal ions are long compared with the flux variability timescales. The large distances we find provide a challenge to current outflow models. For example, these outflows cannot be connected with an accretion disk surrounding the supermassive black hole as assumed in some models. Furthermore, the outflows may be out of equilibrium as we find in Mrk 509. In this case, a thorough understanding of time-dependent photoionization effects is necessary. In this thesis, I include early steps toward understanding time-dependent photoionization as well as ionization studies of accretion disk winds. The main results of these theoretical studies is that 1) the appearance of multiple ionization components in an outflow can be an artifact of the incorrect assumption that the outflow is in ionization equilibrium and 2) the shielding gas required in accretion-disk-wind models should have a clear signature in UV spectra, but none has been observed to date.
Ph. D.

The evolution, dynamics and eventual fate of galaxies is largely determined by access to and distribution of their primary fuel: atomic neutral hydrogen. Neutral hydrogen is not only pervasive in the disk of galaxies such as the Milky Way, but can also be found in the hot halo surrounding galaxies. The signatures of hydrogen detected in galactic haloes are caused by three key processes: outflow, due to energetic events associated with the galactic disk; infall, due to interactions with other nearby galaxies or the intergalactic medium; and circulation within the galactic ecosystem. In this thesis, a nearby Galactic supershell GSH 006-15+7 is studied, in order to understand how supershells are able to circulate cold gas between the disk and halo. By analysing HI self-absorption in the shell wall, the spin temperature of the gas is constrained to be cold and dense. Based on the morphology of the supershell and its estimated distance, GSH 006-15+7 has a likely origin in the Sagittarius OB 1 association of young stars. There is also evidence that the shell is transitioning into a chimney structure based on fragmentation at high Galactic latitudes, with an associated ionised hydrogen feature indicating a potential position of break-out into the Milky Way halo. This result is supported by findings in optical emission lines of high energy activity. Anomalous velocity gas deviates from that expected of Galactic rotation, and as such pinpoints hydrogen that is part of the cycle of outflow, infall and circulation. The Galactic All Sky Survey (GASS) of southern-sky neutral hydrogen is used to catalogue anomalous velocity gas in the halo of the Milky Way. Both classical high-velocity clouds and anomalous velocity clouds are included in the catalogue. With their lower velocities, anomalous velocity clouds are intrinsically closer to Galactic rotation and hence can be expected to probe the bridge between the Galactic disk and the halo. The GASS catalogue features unprecedented combination of high sensitivity with high angular and spectral resolution in the southern sky, and will be useful for studies of anomalous velocity gas on various scales. Several GASS clouds are followed up, some of known origin, at high angular resolution with the Australia Telescope Compact Array in order to determine the relative influences of origin and environment in clouds showing evidence of interaction. By combining the population of GASS high-velocity clouds with a very sensitive survey of neutral hydrogen in the halo, a Milky Way halo hidden from typical surveys of neutral hydrogen due to sensitivity limits is revealed, where the brightest neutral hydrogen merges with a diffuse prevalent medium that is likely to contribute just as much gas content as the bright high-velocity clouds. These results are consistent with findings in other wavelengths indicating the presence of more hydrogen in the halo than detected in the high-velocity cloud population. If the detected diffuse gas follows predicted supernova-driven models of cooling, then these two populations of neutral hydrogen combined can potentially account for the entire Galactic star formation rate. Overall, the studies in this thesis have revealed an active and dynamic Galaxy that maintains strong connections between its disk and the surrounding halo environment, in which neutral hydrogen remains a pivotal and powerful key to unlocking its evolutionary past and star-forming future.

``Quasar-mode feedback'' occurs when momentum and energy from the environment of accreting supermassive black hole couple to the host galaxy. One mechanism for such a coupling is by high-velocity (up to $sim$ 0.2c) quasar-driven ionized outflows, appearing as blue-shifted absorption and emission lines in quasar spectra. Given enough energy and momentum, these outflows are capable of affecting the evolution of their host galaxies. This dissertation presents the studies of emission and absorption quasar outflows from different perspectives. (1). By conducting large broad absorption line (BAL) quasar surveys in both Sloan Digital Sky Survey and Very Large Telescopes (VLT), we determined various physics properties of quasar absorption outflows, e.g., the electron number density (ne), the distance of outflows to the central quasar ($R$), and the kinetic energy carried by the outflow ($dot{E}_{k}$). We demonstrated that half of the typical BAL outflows are situated at $R$ $>$ 100 pc, i.e., having the potential to affect the host galaxies. (2). Our group carried out a Hubble Space Telescope program (PI: Arav) for studying the outflows in the Extreme-UV, collaborating with Dr. Gerard Kriss from Space Telescope Science Institute (STScI). We developed a novel method to fit the multitude of quasar absorption troughs efficiently and accurately. We have identified the most energetic quasar-driven outflows on record and discovered the largest acceleration and velocity-shift for a quasar absorption outflow. (3). By using the VLT data, Xu led the project to study the relationships between BAL outflows and emission line outflows. We found possible connections between these two types of quasar outflows, e.g., the luminosity of the [oiii] ly 5007 emission profile decreases with increasing ne derived from the BAL outflow in the same quasar. These findings are consistent with BAL and emission outflows being different manifestations of the same wind, and the observed relationships are likely a reflection of the outflow density distribution.
Doctor of Philosophy
Super massive black holes (SMBHs) are believed to exist in the center of almost all massive galaxies, where the brightest accreting ones are named ``quasars''. ``Quasar-mode feedback'' occurs when momentum and energy from the environment of accreting SMBHs couple to the host galaxy. One mechanism for such a coupling is by high-velocity (up to $sim$ 0.2c) quasar-driven ionized outflows, appearing as blue-shifted absorption and emission lines in quasar spectra. Given enough energy and momentum, these outflows are capable of affecting the evolution of their host galaxies. Such quasar outflows are invoked to explain a variety of observations, e.g., the chemical enrichment of the intergalactic medium (IGM), the shape of the observed quasar luminosity function, and the self-regulation of the growth of the SMBHs. In this dissertation, I focus on studying the emission and absorption outflows observed in quasars spectra, collected with the largest telescopes and most powerful instruments in the world. (1). By conducting large broad absorption line (BAL) quasar surveys in both Sloan Digital Sky Survey and Very Large Telescopes (VLT), we determined various physics properties of quasar absorption outflows, e.g., the electron number density (ne), the distance of outflows to the central quasar ($R$), and the kinetic energy carried by the outflow ($dot{E}_{k}$). We demonstrated that half of the typical BAL outflows are situated at $R$ $>$ 100 pc, i.e., having the potential to affect the host galaxies. (2). Our group carried out a Hubble Space Telescope program (PI: Arav) for studying the outflows in the Extreme-UV, collaborating with Dr. Gerard Kriss from Space Telescope Science Institute (STScI). We developed a novel method to fit the multitude of quasar absorption troughs efficiently and accurately. We have identified the most energetic quasar-driven outflows on record and discovered the largest acceleration and velocity-shift for a quasar absorption outflow. (3). By using the VLT data, Xu led the project to study the relationships between BAL outflows and emission line outflows. We found possible connections between these two types of quasar outflows, e.g., the luminosity of the [oiii] ly 5007 emission profile decreases with increasing ne derived from the BAL outflow in the same quasar. These findings are consistent with BAL and emission outflows being different manifestations of the same wind, and the observed relationships are likely a reflection of the outflow density distribution.

In this thesis, I present 4 new, high-resolution observations of the Galactic microquasar SS 433, obtained from the Very Long Baseline Array (VLBA). I show that we can resolve the same ejecta in successive observations separated by ~ 35 d. I will demonstrate a method to uniquely determine launch vectors of the jet bolides, and I use this unprecedented baseline in time to show that the expansion rate of these bolides may reach 0.03c. I also present the first scientific results from the study of the radio jets in a unique set of historic observations of SS 433: the 39 images that comprise the 2003 VLBA movie of Mioduszewski et al. (2004). This unmatched time sampling allows us to see daily changes in the dynamics of SS 433's jets. I present evidence that these observations caught SS 433 as it transitioned from quiescence into a flare, and I show that this manifests itself as an increase in both the jet launch speed and the brightness of the jet bolides. Using these data, I examine the evolution of the particle energies, densities and magnetic fields within the bolides. We see that the estimates of the mass-loss rates via the jets cannot be reconciled with the those inferred from X-ray or optical data, if we posit equipartition of energy in synchrotron emitting plasma. The time resolution of the 2003 data allows us to observe the flux evolution of the jet bolides, and I show that the bolides undergo a power law decay as t^−2.8. Lastly, I examine X-ray monitoring data from the Swift/BAT satellite and the MAXI All-Sky- Monitor. From these lightcurves, I examine the geometry of the X-ray emission from close to the compact object itself, and I discuss SS 433's place within the current paradigm of accretion in microquasars. Throughout, we will see that it is the accessible time scales of the SS 433 phenomenon that allow us to learn about its exciting, complex physics.

This thesis presents a study of ionised outflows and multi-wavelength variability of Active Galactic Nuclei (AGN) focusing on three Seyfert-type objects: NGC 3516, Mrk 509 and ESO 113-G010. For this work I have made use of mostly XMM-Newton data, i.e. high-resolution X-ray spectra from the Reflection Grating Spectrometer (RGS) for exploring the ionised outflows, and simultaneous optical/UV/X-ray data from the Optical Monitor (OM) and the European Photon Imaging Camera (EPIC) instruments to study the intrinsic emission and variability. I have investigated the structure and geometry of the partial-covering multi-phase ionised absorber of NGC 3516. I demonstrate that the X-ray variability, originally attributed to occultation by a cloud in an accretion disc wind passing in front of the source, is rather the result of changes in the intrinsic emission of the source. From a 100-day multi-wavelength campaign on Mrk 509, I find that the character of its variability, strictly correlated in the UV and soft X-ray bands, indicates that the soft X-ray excess emission is produced by Compton reprocessing of the UV disc emission in a warm corona encasing the inner disc. I have also studied the nuclear obscuration and the role of dust in the warm absorber of ESO 113-G010. I show that the cause of significant optical/UV reddening, despite the lack of X-ray absorption from neutral gas, is most likely to be dust embedded in a weakly-ionised phase of an absorber which is conspicuous in the high-resolution X-ray spectrum of this object. I have explored the uncertainties in the irradiating spectral energy distribution due to the nuclear obscuration of the source and the effects these have on the survival of the dust, on the thermal stability of the warm absorber phases and the ionisation balance calculations required for photoionisation modelling. From my case-studies of these three objects emerges a more detailed picture of the ionised outflows phenomenon and of the environment in the vicinity of the nuclear supermassive black holes in AGN.

Active Galactic Nuclei (AGN) are axisymmetric systems to first order; their observed properties are likely strong functions of inclination with respect to our line of sight. However, except for a few special cases, the specific inclinations of individual AGN are unknown. We have developed a promising technique for determining the inclinations of nearby AGN by mapping the kinematics of their narrow-line regions (NLRs), which are easily resolved with Hubble Space Telescope (HST) [O III] imaging and long-slit spectra from the Space Telescope Imaging Spectrograph (STIS). Our studies indicate that NLR kinematics dominated by radial outflow can be fit with simple biconical outflow models that can be used to determine the inclination of the bicone axis, and hence the obscuring torus, with respect to our line of sight. We present NLR analysis of 52 Seyfert galaxies and resultant inclinations from models of 17 individual AGN with clear signatures of biconical outflow. From these AGN, we can for the first time assess the effect of inclination on other observable properties in radio-quiet AGN, including the discovery of a distinct correlation between AGN inclination and X-ray column density.

Supermassive black holes (BHs) and their host-galaxies are thought to evolve in tandem, with the energy output from the rapidly-accreting BH regulating star formation and the growth of the BH itself. The goal of better understanding this process has led to much work focussing on the properties of quasars at high redshifts, $z\gtrsim 2$, when cosmic star formation and BH accretion both peaked. At these redshifts, however, ground-based statistical studies of the quasar population generally have no access to the rest-frame optical spectral region, which is needed to measure H$\beta$-based BH masses and narrow line region outflow properties. The cornerstone of this thesis has been a new near-infrared spectroscopic catalogue providing rest-frame optical data on 434 luminous quasars at redshifts $1.5 \lesssim z \lesssim 4$. At high redshift, $z \gtrsim 2$, quasar BH masses are derived using the velocity-width of the CIV broad emission-line, based on the assumption that the observed velocity-widths arise from virial-induced motions. However, CIV exhibits significant asymmetric structure which suggests that the associated gas is not tracing virial motions. By combining near-infrared spectroscopic data (covering the hydrogen Balmer lines) with optical spectroscopy from SDSS (covering CIV), we have quantified the bias in CIV BH masses as a function of the CIV blueshift. CIV BH masses are shown to be over-estimated by almost an order of magnitude at the most extreme blueshifts. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H$\alpha$) we derive an empirical correction to all CIV BH-masses. The correction depends only on the CIV line properties and therefore enables the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars. Quasars driving powerful outflows over galactic scales is a central tenet of galaxy evolution models involving 'quasar feedback' and significant resources have been devoted to searching for observational evidence of this phenomenon. We have used [OIII] emission to probe ionised gas extended over kilo-parsec scales in luminous $z\gtrsim2$ quasars. Broad [OIII] velocity-widths and asymmetric structure indicate that strong outflows are prevalent in this population. We estimate the kinetic power of the outflows to be up to a few percent of the quasar bolometric luminosity, which is similar to the efficiencies required in recent quasar-feedback models. [OIII] emission is very weak in quasars with large CIV blueshifts, suggesting that quasar-driven winds are capable of sweeping away gas extended over kilo-parsec scales in the host galaxies. Using data from a number of recent wide-field photometric surveys, we have built a parametric SED model that is able to reproduce the median optical to infrared colours of tens of thousands of AGN at redshifts $1 < z < 3$. In individual objects, we find significant variation in the near-infrared SED, which is dominated by emission from hot dust. We find that the hot dust abundance is strongly correlated with the strength of outflows in the quasar broad line region, suggesting that the hot dust may be in a wind emerging from the outer edges of the accretion disc.

Questo lavoro di tesi si propone di esaminare la simulazione di una galassia isolata simile alla Via Lattea e, in particolare, di analizzare i processi di feedback dovuto ad esplosioni di supernove, il meccanismo responsabile della generazione di outflow gassosi dal disco. Scopo della tesi è quello di testare la validità dei risultati ottenuti dalla simulazione (generata dal recente modello di feedback SMUGGLE presente nel codice a griglia mobile AREPO) dal punto di vista della formazione stellare, del tasso di esplosioni di supernove e dei fenomeni di outflow di gas su scala galattica. Sono stati indagati vari andamenti evolutivi delle proprietà cinematiche del gas, della formazione stellare e dell'efficienza di rilascio di energia/impulso da parte delle supernove al fine di ricercare relazioni che mettano in luce lo stretto legame tra questi processi astrofisici. La simulazione è stata in grado di generare fenomeni di esplusione di gas in maniera auto-consistente e, in combinazione con l'esaurirsi del gas a causa della formazione stellare, ha condotto la galassia a regolare il suo tasso di formazione stellare e quello relativo alle esplosioni di supernove a dei livelli in accordo con le osservazioni. Inoltre la simulazione è stata in grado di riprodurre la relazione osservativa di Kennicutt-Schmidt. Infine questo lavoro di tesi ha evidenziato una possibile connessione tra la variazione del tasso di densita' superficiale di formazione stellare (SFRD) e l'ammontare di massa di gas esplusa dal disco. Ciò è stato fatto al fine di valutare l'esistenza di un possibile valore critico per la SFRD tale per cui, al di sopra di questa soglia, si possano chiaramente osservare fenomeni di espulsione di gas su scala galattica. I risultati ottenuti però non mostrano evidenze dell'esistenza di un tale valore e che ulteriori approfondimenti e simulazioni di confronto sono necessari per avvalorare questi risultati preliminari.

Dans l’Univers, on observe des galaxies lointaines ne formant plus d’étoiles, mais les astrophysiciens n’ont pas encore identifié avec certitude les phénomènes physiques à l’origine de leur “mort”. Pour apporter des éléments de réponse, je me suis penchée sur l’étude de phénomènes qui pourraient y jouer un rôle : les processus de rétroaction des étoiles et des trous noirs supermassifs actifs, la formation stellaire, et les vents galactiques. Le Chapitre 1 présente toutes les notions nécessaires à la compréhension du problème : les caractéristiques des galaxies typiques de l’Univers proche et lointain ; les vents galactiques ; la mort des galaxies; les trous noirs supermassifs actifs (noyaux actifs de galaxies, AGN) et les étoiles ; et leur rétroaction. Dans le Chapitre 2, je présente les techniques numériques utilisées : le code de simulations astrophysiques RAMSES et le code de transfert radiatif Cloudy, que j’ai utilisé pour développer une méthode de calcul de l’état d’ionisation d’une galaxie, détaillée au Chapitre 3. Le Chapitre 4 étudie le couplage entre les trous noirs actifs et les étoiles, avec le projet POGO, Origines Physiques des Vents Galactiques. Durant cette thèse, j’ai montré que les trous noirs actifs n’étaient pas en mesure de tuer subitement leur hôte, même en prenant en compte la rétroaction des étoiles, et que leur couplage peut réduire ou renforcer les vents dans les galaxies en fonction de leur masse. Le Chapitre 5 fait un état de l’art du domaine avant et pendant mon doctorat, reprend les conclusions de cette thèse et donne quelques perspectives, notamment en ce qui concerne le rôle additionnel des rayons cosmiques dans la mort des galaxies
In the Universe, we observe galaxies forming no, or almost no, stars anymore, but astrophysicists do not know yet what physical mechanisms cause their “death”. To give clues to solve the problem, I studied feedback processes from stars and active supermassive black holes, star formation and galactic outflows. Chapter 1 presents all the notions to understand the problem: the characteristics of typical galaxies in the local and distant Universe, galactic outflows, galaxy death, active supermassive black holes, stars, and their feedback processes. In Chapter 2, I describe the numerical techniques I used: the simulation code RAMSES, and the radiative transfer code Cloudy, which I used to develop a computation method to get the ionization state of an entire galaxy. This method is presented in Chapter 3. Chapter 4 studies the coupling between the feedback processes of active supermassive black holes and stars, with the POGO project, Physical Origins of Galactic Outflows. During this thesis, I showed that typical active supermassive black hole cannot suddenly kill their host, even when stellar feedback processes are accounted for, and that their coupling either reduces or enhances the mass outflow rate depending on the mass of the host. In Chapter 5, I give a state-of-the-art about active supermassive black holes before and during my thesis, sum up the conclusions of the work, and give perspectives to enlarge the scope of the study, especially regarding the additional role of cosmic rays in the death of galaxies

2008/2009
In this thesis we study the effect of galactic fountains, namely gas and flows from the disk of galaxies produced by multiple supernova explosions, on the chemical evolution of galaxies. Sequential supernova explosions create a superbubble, whereas the swept up interstellar medium is concentrated in a supershell which can break out a stratified medium, producing bipolar outflows. The gas of the supershells can fragment into clouds which eventually fall toward the disk producing so-called galactic fountains. Many works in literature have dealt with superbubble expansion in stratified media. However, very few papers in the past have taken into account the chemical evolution of the superbubble and how the supershell get polluted from the metals produced by supernova explosions. With this thesis for the first time the effect of galactic fountains we consider in a detailed chemical evolution model for the Milky Way. In the first part of our work we study the expansion law and chemical enrichment of a supershell powered by the energetic feedback of a typical Galactic OB association at various galactocentric radii. We follow the orbits of the fragments created when the supershell breaks out and we compare their kinetic and chemical properties with the available observations of high - and intermediate - velocity clouds. We use the Kompaneets (1960) approximation for the evolution of the superbubble driven by sequential supernova explosions and we compute the abundances of oxygen and iron residing in the thin cold supershell. Due to Rayleigh-Taylor instabilities we assume that supershells are fragmented and we follow the orbit of the clouds either ballistically or by means of a hybrid model considering viscous interaction between the clouds and the extra-planar gas. We find that if the initial metallicity is solar, the pollution from the dying stars of the OB association has a negligible effect on the chemical composition of the clouds. The maximum height reached by the clouds above the plane seldom exceeds 2 kpc and when averaging over different throwing angles, the landing coordinate differs from the throwing coordinate by only 1 kpc. Therefore, it is unlikely that galactic fountains can affect abundance gradients on large scales. The range of heights and [O/Fe] ratios spanned by our clouds suggest that the high velocity clouds cannot have a Galactic origin, whereas intermediate velocity clouds have kinematic properties similar to our predicted clouds but have observed overabundances of the [O/Fe] ratios that can be reproduced only with initial metallicities which are too low compared to those of the Galaxy disk. Even if it is unlikely that galactic fountains can affect abundance gradients on large scales, they can still affect the chemical enrichment of the interstellar medium (ISM) because of the time-delay due to the non-negligible time taken by fountains to orbit around and fall back into the Galaxy. This implies a delay in the mixing of metals in ISM which conflicts with the instantaneous mixing approximation usually assumed in all models in literature. We test whether relaxing this approximation in a detailed chemical evolution model can improve or worsen the agreement with observations. To do that, we investigate two possible causes for relaxing of the instantaneous mixing: i) the ``galactic fountain time delay effect'' and ii) the ``metal cooling time delay effect''. We find that the effect of galactic fountains is negligible if an average time delay of 0.1 Gyr, as suggested by our model, is assumed. Longer time delays produce differences in the results but they are not realistic. The metal cooling time delays produce strong effects on the evolution of the chemical abundances only if we adopt stellar yields depending on metallicity. If, instead, the yields computed for the solar chemical composition are adopted, negligible effects are produced, as in the case of the galactic fountain delay. The relaxation of the IMA by means of the galactic fountain model, where the delay is considered only for massive stars and only in the disk, does not affect the chemical evolution results. The combination of metal dependent yields and time delay in the chemical enrichment from all stars starting from the halo phase, instead, produces results at variance with observations.
XXII Ciclo
1979

Les recherches que j’ai menées durant ma thèse traitent de trois grands défis en formation stellaire : contraindre par les observations les phases précoces de la formation des étoiles massives – le stade préstellaire, déterminer l’origine des masses stellaires et caractériser les processus d’accrétion-éjection de la phase protostellaire.Dépasser les paradigmes actuels en formation stellaire nécessite d’étudier des régions de formations d’étoiles plus représentatives des processus typiques dans la Voie Lactée. C’est dans ce but que j’ai travaillé sur des observations ALMA de W43-MM1, un jeune proto-amas situé à 5500 pc du Soleil présentant un taux de formation stellaire élevé. J’ai d’abord identifié et caractérisé les cœurs sur la carte continuum. J’ai découvert 131 cœurs avec des tailles typiques de 2400 ua et des masses entre 1 et 100 Msol. La distribution en masse de ces cœurs (CMF) montre au-dessus de 1.6 Msol une pente de -0.96 +/- 0.13 significativement plus plate que celle de l’IMF de référence sur cet intervalle de masse, -1.35. Cela signifie une surabondance de cœurs massifs – et donc d’étoiles massives – par rapport au nombre attendu dans les modèles actuels de formation stellaire. Les explications possibles impliquent soit que la formation d’étoiles est atypique dans W43-MM1 (variabilité dans notre galaxie), soit que les étoiles massives se forment dans les amas sur des échelles de temps différentes des étoiles de type solaire (la formation d’étoiles ne serait pas un processus continu).J’ai ensuite caractérisé ces cœurs en utilisant les raies de CO(2-1) et SiO(5-4) et révélé un riche amas de flots protostellaires constitué de 46 lobes venant de 27 cœurs couvrant tout l’intervalle de masse et incluant 11 cœurs massifs (avec des masses supérieures à 16 Msol ). J’ai aussi utilisé la détection de molécules organiques complexes, des traceurs d’environnements chauds, comme un autre indicateur d’activité protostellaire. 12 des 13 cœurs massifs sont finalement apparus comme étant protostellaires, laissant un seul bon candidat cœur préstellaire massif. Ces statistiques interrogent sur l’universalité de la phase préstellaire pour les cœurs massifs et suggèrent que le modèle du cœur turbulent ne peux s’appliquer partout. Les flots protostellaires permettent aussi de reconstituer l’historique des processus d’accrétion/éjection. J’ai étudié la cinématique des nœuds constituant les jets moléculaires à haute vitesse en utilisant des diagrammes position-vitesse. J’ai montré que la complexité des structures en vitesse de ces nœuds cache une forte variabilité, et évalué le temps caractéristiques entre deux éjections à environ 500 ans. Ces échelles de temps sont similaires à celles mesurés entre deux sursauts d’accrétion pour les étoiles de type FU-Orionis
The research I have performed during my PhD addresses three major challenges of the star formation field: constraining, observationally, the earliest phases of high-mass star formation – the so-called prestellar stage, studying the origin of the stellar masses, and characterizing the process of protostellar accretion-ejection.Going beyond the current paradigms of star formation requires studying star-forming regions which are more representative of the general mode of star formation in the Milky Way. To this purpose I have used ALMA observations of W43-MM1, a young located at 5.5 kpc distance from the Sun, which presents a high star formation rate. The first step of my work has been to identify and characterize cores in the continuum image. I discovered 131 cores about 2400 AU in size which have mass between 1 and 100 Msun. I measured their mass distribution (CMF) and found a slope of -0.96 +/- 0.13 on 1.6 - 100 Msun that is markedly flatter than the reference Salpeter slope of the IMF on that range, -1.35. This means an overabundance of high-mass cores - and thus high-mass stars -compared to the number expected by the current models of star formation. Possible explanations imply either that star-formation is atypical in W43-MM1 (variably in the Milky Way) or that high-mass stars form at different time than low-mass stars in a cluster (star formation would not be a continuous process).I have characterized these cores using CO(2-1) and SiO(5-4) lines and revealed a rich cluster of 45 outflow lobes from 27 cores covering the whole mass range and including 11 high-mass cores (M>16 Msun). I have also used the detection of Complex Organic Molecules (COMs), typically detected in warm environments like hot cores, as indicator of the protostellar activity. 12 out of the 13 high-mass cores in W43-MM1 have eventually been characterized as protostellar, leaving one good high-mass prestellar core candidate. These statistics raises question about the universality of a prestellar phase for high-mass stars and suggests that the core-fed models for high-mass star formation cannot generally apply. The protostellar outflows also bring valuable information on the accretion/ejection history. I have studied the kinematics of high-velocity molecular jets that divide into knots using Position-Velocity diagrams. I have shown that the complex velocity structures of these knots hide a strong variability, and evaluated the associated timescale between two ejections to be about 500 yr. This is reminiscent of the values obtained between accretion burst in FU Orionis stars

博士
國立中央大學
天文研究所
103
In this thesis I present studies of the kinematics and the physical properties of molecular gas galactic nuclei. Two representative bar galaxies; (1) NGC 1097, (2) our own Galactic center, are studied. The nucleus of NGC 1097 consists of a molecular concentration, ~350 pc in scale, and a starburst ring, ~kpc in scale. To better depict the kinematics and the star formation of the nucleus, the SubmilliMeter Array (SMA) and the Hubble Space Telescope (HST) are used to obtain high angular resolution CO(J = 2-1) line and the Pa_alpha line images. The unprecedented high resolution reveals that the turbulent/diffuse molecular gas (V ~90 km/s) is associated with the dust lane. The less turbulent/dense molecular gas (V ~45 km/s) could be determined to be associated with the starburst ring. The variations of the physical properties of the molecular gas are associated with the large scale dynamics. However, the star formation rate is not significantly affected by such dynamics. For similar type of galaxies, this work initiated the quantitative measurements of the evolution of star formation in the kilo-parsec starburst ring. The high-J dense gas in the nuclear region of NGC 1097 are investigated with the HCN(J = 3-2) and HCO+(J = 3-2) lines observed by SMA. The purpose is to resolve and study the enhancement of the HCN abundance in the vicinity of the Seyfert 1 nucleus. In the nuclear concentration of NGC 1097, the HCN(J = 3-2) line is found to contribute 30% to the total HCN(J = 3-2) line flux. A self-consistent check of the fractional abundance enhanced by X-ray ionization chemistry of the nucleus is possible with our observation, and the results are consistent with the X-ray chemical model. In addition, the HCN(J = 3-2) and HCO+(J = 3-2) emission lines are optically thin and they show tight intensity correlation with the Spitzer 24 micron-meter emission in the starburst ring. The CO(J = 3-2) line is optically thick and shows poor correlation with the 24 micron-meter emission. This suggests that the dense molecular gas and the dust are of the same origins: the star-forming region hundred-pc scale. Next studies on the Galactic Cener (GC) are presented. I obtained the first CS(J = 4-3) and CS(J = 5-4) maps of GC with the Caltech Submillimeter Observatory (CSO). The main purpose is to study the polar arc, which is a molecular ridge near the SgrA region, with apparent non-coplanar motions and acceleration perpendicular to the Galactic disk. With the new high-J CS maps, a new component in the ridge smoothly connecting the Polar Arc and the Galactic disk is found. This new component is the brightest in the CS(J = 4-3) line. The physical conditions of this new component can be determined using the rotational diagrams and the statistical equilibrium calculation. I found the physical conditions (density, temperature) to produce highest opacity of this new component in the CS(J = 4-3) line. This suggests that this new component is intrinsically the brightest in the CS(J = 4–3) line. I also lead a project to map the entire central molecular zone (CMZ) of the GC with the CS(J = 2-1) line using the Nobeyama 45m telescope. I present the early results of the central 30 pc of the CMZ in the last part of this thesis. With the low velocity molecular gas surrounding the 20 cm radio halo, I identify a possible expanding shell with a size of ~30 pc near the SgrA complex. In addition, a possible outflow expanding/accelerating perpendicular to the Galactic plane cloud be found. The time scales of these features are 100000 years, which can not be driven by the Galactic center supernova SgrA East (~10000 years). This large scale outflow could be produced by >8 supernova explosions 100000 years ago.

碩士
國立中央大學
天文研究所
101
In the second half of 2010, Fermi satellite discovered two giant gamma ray bubbles above and below our Galactic plane in the direction of the Galactic center. The bubbles extended 50 degrees in Galactic latitude and 40 degrees in longitude. The spatial distributions correlated with the ROSAT X-ray map at 1.5 keV and the WMAP haze near the Galactic plane. Among many possible origins of the bubbles, we are particular interested in the scenario that stars are repeatedly captured by the supermassive black hole located at the Galactic center. At each capture, a huge amount of energy is release and causes a massive expansion or outflow that forms the bubbles. We adopt the astro-hydrodynamic code PLUTO to study this phenomenon. We carry out 2D (cylindrical coordinates) numerical survey on the formation and evolution of the bubbles under different conditions, such as different energy release at each capture and different time intervals between captures. We also consider the effect of different assumed scale heights of the Galactic gaseous disk. When we compare different single capture cases (with same scale height), we learn that the shape of the bubble from small energy release is rounder and extended further in the lateral direction than the one from large energy release, but the perturbation is weaker. When the energy release is large, the bubble can easily penetrate the disk, but the lateral extend is restricted to about three times the scale heights. The morphology of a single capture case and a repeated captures case with the same total energy is significantly different. The repeated captures case has lesser lateral evolution and a lot more turbulent interior. Moreover, the turbulent level increases when the interval between captures decreases. The X-ray maps from simulations show that the repeated captures cases have slightly thick lower bubble edge than the single capture cases. We also compare the maps with ROSAT data.

Galactic outflows play an important role in the formation and evolution of galaxies by regulating the star formation rate (SFR) within them and by throwing out metals into the intergalactic medium (IGM). They are key to understand the relation between the stellar and the dark matter halo mass, mass-metallicity relation of galaxies, intergalactic metal enrichment, formation of high velocity clouds and much more. Galactic outflows have been observed to be present in galaxies at all redshifts either in emission or in absorption of the stellar continuum. Outflows have been also detected in the immediate vicinity of galaxies by probing absorption lines in the spectrum of background Active Galactic Nuclei. In this thesis we explore the interactions between supernovae (SNe) driven outflows and the circumvallate medium (CGM), an extended hot gas atmosphere believed to be present in the haloes of massive (stellar mass, M? & 1010 M_) galaxies. Given the complexity of geometry and multiphase nature of outflows, we use numerical simulations to study gas interactions. Our results shine light on many interesting aspects of the galactic outflows, such as, i) the effect of the circumgalactic medium on the mass outflow rate and velocity of the outflowing gas on large scales, ii) origin of high velocity cold (_ 104 K) gas in outflows iii) origin of X-ray emission in different scenarios. We connect our numerical and analytical work with the X-ray data. We also use our numerical set up to understand the origin and nature of two giant -ray bubbles, called the Fermi Bubbles, at the centre of our Galaxy. We compare our synthetic emission models to the observed -rays, X-rays, radio and UV absorption data and constrain the energetics and age of these bubbles. Below we outline the investigations undertaken in this thesis and point out our main results. Interaction of circumgalactic medium and outflows In a standard SNe driven outflow scenario, SNe ejected gas is a continuous outflow that expands freely with or without the gravity of the galaxy (Chevalier & Clegg 1985; Sharma & Nath 2013). The multiphase nature of the outflowing gas and the resistance provided by the CGM is often neglected while estimating the total mass outflow rate from galaxies (Arribas et al. 2014; Heckman et al. 2015). In the presence of a CGM, this scenario can change completely as the wind does not remain in a steady state anymore and involves far more complexities than typically considered, such as mixing with the hot CGM. The dynamics of the cold gas is expected to be different in such a non-steady state compared to the calculations in which the cold clumps move under the effect of a steady state wind. To study these effects, we perform hydrodynamical simulations of SNe driven outflows in a Milky-Way type galaxy that includes a CGM. We assess the effects of the CGM on the outflow by varying the star formation rate. We find that the total mass outflow rate is divided almost equally in two phases that peak at _ 105 K (warm) and at _ 3_106 K (hot). This means that observations in optical/UV or X-ray only probe a fraction of the outflowing mass. We also find that the mass loading factor (_), defined as the ratio between mass outflow rate to the star formation rate, at outer radii (_ 100 kpc) of a galaxy can be much higher than the rate observed in warm gas (_ _ 0:3-0:5). We present simple scaling relations between the mass loading factor in warm gas and the total mass loading factor at the virial radius (_v) that can be used to estimate the total mass outflow rate from such galaxies. We also find that warm gas can be entrained by _ 1000 km s􀀀1 free wind to reach velocities as large as _ 700 km s􀀀1. Cold clouds also form at the interaction zone between the outflow and the CGM. Some of these clouds keep moving outwards while some of them fall back to the stellar disc due to gravity. This galactic fountain gas which falls back can lead to further star formation in the disc. X-rays from galaxies Diffuse X-ray emission in case of a standard SNe driven outflow is dominated by the central part of the wind where temperature is _ 107 K and density is & 0:1 MP cm􀀀3 . Since density at the centre of a standard SNe driven outflow is simply proportional to the star formation rate (SFR), the X-ray luminosity (LX) is expected to be proportional to the SFR2. Observations, however, indicate a linear, or even a sub linear relation between LX and SFR (Mineo et al. 2012b; Wang et al. 2016). We used analytical results and numerical simulations to understand the origin of the X-ray emission from the star forming galaxies. We find that for highly star forming galaxies with no CGM, the diffuse X-ray mainly comes from the centre of the SNe wind as expected. However, for massive galaxies with low star formation rate (. 1 M_ yr􀀀1), the emission is dominated by the contribution from the CGM. This contamination results in a flatter LX-SFR relation than typically expected from a pure SNe driven outflow. Even after we increased the contribution from the outflowing wind by enhancing the mass loading factor to its maximum value, the CGM contamination could not be ignored. We further argue that these high LX values of low star forming, massive galaxies could be inverted to study the properties of the CGM itself Multi-wavelength properties of outflow and Fermi Bubbles in our Galaxy Observations reveal two giant (_ 50_) gamma-ray bubbles, called the Fermi Bubbles (FBs) toward the centre of our Galaxy (Su et al., 2010; Ackermann et al., 2014) the origin of which is still a mystery. Observations in other wavebands such as X-ray, radio and UV (absorption lines) also revealed many other interesting features associated with the FBs. There have been a number of attempts to explain the gamma-ray brightness and spectrum by considering feedback from the Galactic centre black hole (GCBH) and cosmic ray diffusion (Guo et al., 2012; Yang et al., 2012; Zubovas & Nayakshin, 2012). The required mechanical luminosity in these models exceeds the value that is achievable with the current accretion rate by a few orders of magnitude. Star formation driven wind models have been, however, under-investigated so far with much less attention to explain the multi-wavelength features related to the FBs. To understand the origin and nature of these bubbles, we simulate SNe driven wind scenario appropriate for the Milky-Way. By using the information about morphology and X-ray emission, we find that the required star formation rate at the centre of our Galaxy is _ 0:5 M_ yr􀀀1. After comparing the synthetic microwave surface brightness from our simulation with the observed data, we constrain the magnetic field inside the bubbles to be _ 4_G. We also find that the gamma-ray morphology and spectral signatures in our simulated bubbles closely resemble the observed ones. The cold gas (< 105 K) kinematics in our simulations also have a similar behaviour, to some extent, as observed in UV absorption lines through the northern bubbles. O viii and O vii line ratio through Fermi Bubbles Most of the models of the Fermi Bubbles focus on getting a reasonable gamma-ray morphology and spectrum by varying the mechanical luminosity of the central source. Other ways to determine the origin of the FBs include probing the bubbles in X-rays to obtain information about the strength of the explosion at the Galactic centre. X-ray spectral analysis by Kataoka et al. (2013) suggests that the shock velocity is _ 300 km s􀀀1 with an age of _ 20 Myr for the bubble, whereas, by analysing the O viii and O vii line ratio Miller & Bregman (2016) obtained a shock speed of _ 500 km s􀀀1 , indicating an age of _ 4 Myr. We simulate both star formation driven and GCBH driven wind scenarios in our Galaxy with varying strength of star formation and accretion rate. We consider a self consistent gas distribution for the Milky-Way CGM that is close to the observations. We compare the synthetic O viii and O vii lines from our simulations with the observations of Miller & Bregman (2016) and find that the data indicates a shock velocity of _ 300 km s􀀀1 and a corresponding age of the bubbles to be 15-25 Myr. After considering possible electron-proton non-equilibrium in the shocked gas that can affect the observability of the X-ray lines, we rule out mechanical luminosities & 1041 erg s􀀀1 as the possible driver of the Fermi Bubbles.

The X-ray spectral variability of Active Galactic Nuclei typically follows a “softer when brighter” trend, which is believed to be originated mainly from the superposition of different spectral components, varying independently from each other, although some intrinsic variations of the continuum are also possible. We analyzed the MEXSAS sample, made up by more than 7800 observations from 2700 quasars from the fifth release of the XMM-Newton Serendipitous Source Catalogue (3XMM-SSC), cross-matched with two quasar catalogues, SDSS-DR7Q and SDSS-DR12Q. We developed a technique that is able to compute estimates of the photon index from approximate spectral fits, using the fluxes in the catalogue. Following Trevese & Vagnetti (2002), we quantify the spectral variability using β = −∆Γ/∆ log F. We find an ensemble softer when brighter trend, extending therefore this result to quasars, and the same result is found for eight single sources extracted from the catalogue, plus one (PG 1114+445) discarded because of the presence of a prominent warm absorber, although with different extent. To investigate the reason for this range of different values of beta, we investigated a sample of X-ray bright sources taken from the samples of Sobolewska & Papadakis (2009), plus M81, for which it is possible to obtain accurate photon indices. We compute both the accurate and approximate photon indices and we confront β obtained with both methods. Finally, we studied the spectra of 13 observations of PG 1114+445, finding multiple absorbers, one possibly being a highly ionized, ultra-fast outflow, with velocity of about 15% of the speed of light, which is observable in four observations.

Evolution of galaxies is a phenomenon that affects the formation and composition of galaxies, and the intergalactic medium. It is mediated by processes that establish a symbiotic relationship between a galaxy and the surrounding circum-galactic medium (CGM) by enabling the exchange of mass, momentum, energy, and metals between the two. For star-forming galaxies, one side of the exchange is driven by galactic outflows (GOs) emerging from supernovae explosions (SNes). GOs posses a complex, multiphase structure which covers several orders in magnitudes of density and temperature. A complete description of GOs should be able to capture all its characteristics and replicate its multi-wavelength observations. Due to its complicated phase structure, analytical modelling of GOs is limited in scope and therefore, significant effort in this field is devoted to the simulations of these outflows. In this thesis, we use idealised simulations of isolated galaxies to understand GOs from star-forming Milky Way (MW) -type galaxies. We consider the evolution of the outflowing gas over several Myr and focus on the properties of the extraplanar gas. We produce synthetic observations which we compare with existing X-ray and radio observations. By conducting simulations with various star formation rates, we connect the properties of the extraplanar gas with the underlying star formation occurring in the disc. We study the different thermal phases and their kinematical and dynamical properties in GOs as they travel through the CGM. To quantify the interactions taking place between the different phases, we analyse simulations of a local patch of the solar neighbourhood.

Clusters of galaxies are host to powerful Active Galactic Nuclei (AGN) that greatly affect the thermal history of clusters. By keeping X-ray emitting gas from cooling, massive, run away star formation does not occur in the brightest cluster galaxy (BCG). This is achieved through radio jets displacing large quantities of metal-rich gas and carving out cavities in the intracluster medium (ICM). This metal-rich gas was originally formed within the BCG and ejected through type Ia supernovae. The current distribution of the ejecta suggests an extra source of energy has spread the material far out into the ICM. Currently, it is unclear what mechanisms are responsible. In this thesis, I present evidence, in the form of X-ray imaging and spectra, that establishes a link between AGN and the observed distribution of metal-rich gas. First, the BCG in the Abell 1664 cluster is unusually blue and is forming stars at a rate of ~23 solar masses per year. The BCG is located within 5 kpc of the X-ray peak, where the cooling time of 3.5×10^8 yr and entropy of 10.4 keV cm^2 are consistent with other star-forming BCGs in cooling flow clusters. The cooling rate in this region is roughly consistent with the star formation rate, suggesting that the hot gas is condensing onto the BCG. We use the scaling relations of Birzan et al. (2008) to show that the AGN is underpowered compared to the central X-ray cooling luminosity by roughly a factor of three. We suggest that A1664 is experiencing rapid cooling and star formation during a low-state of an AGN feedback cycle that regulates the rates of cooling and star formation. Modeling the emission as a single temperature plasma, we find that the metallicity peaks 100 kpc from the X-ray center, resulting in a central metallicity dip. However, a multi-temperature cooling flow model improves the fit to the X-ray emission and is able to recover the expected, centrally-peaked metallicity profile. Next, using deep Chandra observations of the Hydra A galaxy cluster, we examine the metallicity structure near the central galaxy and along its powerful radio source. We show that the metallicity of the ICM is enhanced by up to 0.2 dex along the radio jets and lobes compared to the metallicity of the undisturbed gas. The enhancements extend from a radius of 20 kpc from the central galaxy to a distance of ~120 kpc. We estimate the total iron mass that has been transported out of the central galaxy to be between 2E7 and 7E7 solar masses which represents 10% - 30% of the iron mass within the central galaxy. The energy required to lift this gas is roughly 1% to 5% of the total energetic output of the AGN. Evidently, Hydra A’s powerful radio source is able to redistribute metal-enriched, low entropy gas throughout the core of the galaxy cluster. The short re-enrichment timescale < 1E9 yr implies that the metals lost from the central galaxy will be quickly replenished. Finally, we present an analysis of the spatial distribution of metal-rich gas in 29 galaxy clusters using deep observations from the Chandra X-ray Observatory. The BCGs have experienced recent active galactic nucleus activity in the forms of bright radio emission, cavities, and shock fronts embedded in the hot atmospheres. The heavy elements are distributed anisotropically and are aligned with the large-scale radio and cavity axes. They are apparently being transported from the halo of the BCG into the ICM along large-scale outflows driven by the radio jets. The radial ranges of the metal-enriched outflows are found to scale with jet power as R ~ P^0.43, with a scatter of only 0.42 dex. The heavy elements are transported beyond the extent of the inner cavities in all clusters, suggesting this is a long lasting effect sustained over multiple generations of outbursts. Black holes in BCGs will likely have difficulty ejecting metal enriched gas beyond 1 Mpc unless their masses substantially exceed 1E9 solar masses. It is likely however for these black holes to output enough energy to uplift all the peaked, metal-rich gas beyond the BCG to the currently observed widespread distribution.

The observed properties of galaxies and supermassive black holes (BH) at their centers suggest that there must be a non-gravitational feedback mechanism regulating their evolution. These are the discrepancy at low and high masses between the observed stellar mass function of galaxies and that predicted by ΛCDM models, the scaling relations between the mass of BHs and the velocity dispersion, mass and luminosity of the host galaxy spheroid and the similarity between BH growth and star formation cosmic histories. Models of galaxy formation and evolution in fact routinely include feedback from active galactic nuclei (AGN) and supernovae (SNe), which can successfully reproduce the observed properties cited above. Models consider the following two types of AGN feedback: the radiative mode (or quasar mode), that operates during a luminous AGN phase through winds powered by radiation pressure, and the kinetic (or radio) mode, in which kinetic energy is released by the AGN on longer timescales through relativistic jets, which heat the surrounding halo in galaxy clusters, thus preventing cooling and further accretion on the central galaxy, and consequently further star formation. So far, the clearest observational evidence of AGN feedback comes from the kinetic mode in massive central cluster galaxies. Radiative feedback is instead more elusive, and has been recently revealed in action only in a few luminous quasars around the peak of AGN activity history (z~2), where most powerful outflows are observed. However, it is not possible to study high-z quasar outflows on small spatial scales (<100 pc), being poorly-resolved or even unresolved in observations, due to their large distances. This can lead to systematics and uncertainties in the determination of outflow properties and forces to make some assumptions on them, which further increases the uncertainties on the outflow energetics and complicates the evaluation of the impact of outflows on host galaxies and the comparison with models. On the contrary, due to their vicinity, nearby active galaxies are ideal laboratories to explore in detail outflow properties, their formation and acceleration mechanisms, as well as the effects of AGN activity on host galaxies. This work focuses on investigating the properties of outflows in nearby Seyfert galaxies, the physical conditions of the ionized gas and the interplay between nuclear activity and star formation in the galaxy, thanks to the unprecedented combination of spatial and spectral coverage provided by the integral field spectrograph MUSE at the Very Large Telescope (VLT). We introduce our optically- and X-ray selected sample of nearby Seyferts, called MAGNUM survey. We present our MUSE emission-line flux and kinematic maps of the 10 objects we have analyzed so far, including a star-forming galaxy, NGC 6810, to study the properties of a starburst outflow for comparison as well. We map the ionized gas down to spatial scales as low as ~10 pc. We find ubiquitous ionization cones and outflows with various morphologies and extensions, from a few hundred pc to several kpc. We detect peculiar kinematic features suggestive of outflows with hollow-conical structures. We also identify enhanced linewidths perpendicular to radio jets, which point to a correlation between the presence of jets and perpendicular turbulent or outflowing gas motions. We then focus on a detailed multi-wavelength study of the ionized gas and outflow, in terms of physical properties, kinematics, and ionization mechanisms, in one specific galaxy of our sample, NGC 1365, from MUSE in optical band and Chandra satellite in X-rays. Here we map a kpc-scale biconical outflow ionized by the AGN prominent in [O III], while Hα emission traces star formation in a circumnuclear ring and along the bar of the galaxy. Soft X-rays are mostly due to thermal emission from the star-forming regions, but we manage to isolate the AGN photoionized component which matches the [O III] emission from MUSE. We map the mass outflow rate of the galactic ionized outflow, which matches that of the nuclear X-ray wind and then decreases with radius. The integrated mass outflow rate, kinetic energy rate, and outflow velocity are broadly consistent with the typical relations observed in more luminous AGN. We extend our analysis to the nearby star-forming galaxy NGC 6810, whose bipolar galactic ionized outflow we map with MUSE. We determine the dominant ionization mechanism in the outflow, its density and ionization parameter, discovering the first case of star formation occurring within an outflow in an unambiguously star-forming galaxy. We finally investigate with MUSE also the kinetic AGN feedback, by studying the ionized gas enshrouding the X-ray cavity inflated by radio jets around the massive radio-galaxy 3C 317 at the center of the local cluster Abell 2052. Thanks to MUSE capabilities, by mapping the warm gas filaments enshrouding the bubble we are able to directly measure the expansion velocity of the cavity, which usually is instead assumed or derived from indirect and model-dependent methods.

Massive stars play a key role in the evolution of the Galaxy; hence they are important objects of study in astrophysics. Although they are rare compared to low mass stars, they are the principal source of heavy elements and UV radiation, affecting the process of formation of stars and planets, and the physical, chemical, and morphological structure of galaxies. Star clusters form in dense "clumps" (~few parsecs in size) within giant molecular clouds, while individual stars form in cores (subparsec scale). An important step in the observational study of massive star formation is the identification and characterization of clumps. More detailed studies can then show how these clumps fragment into cores. Studies of clumps in our Galaxy will provide fundamental guidelines for the analysis of other galaxies, where individual clumps and cores cannot be resolved, and provide a catalog of interesting sources for observations of the Milky Way with a new generation of instruments, such as the Atacama Large Millimeter/Submillimeter Array. Large-scale blind surveys of the Galactic plane at millimeter and submillimeter wavelengths have recently been completed, allowing us to identify star forming clumps and improve our understanding of the early stages of massive stars. One of these studies, the Bolocam Galactic Plane Survey (BGPS), mapped the continuum emission at 1.1 mm over a large region of the northern Galactic plane at a resolution of 33'', identifying 8559 compact sources throughout the Galaxy. In this dissertation, I present observations of a sample of sources from the BGPS catalog, obtained with the Submillimeter High Angular Resolution Camera II (SHARC-II). I present in this work 107 continuum emission maps at 350 microns at high angular resolution (8.5'') toward clump-like sources and construct a catalog of BGPS substructures. I estimate clump properties such as temperatures and multiplicity of substructures, and compare my results with 350 microns continuum maps from the Hi-GAL survey. I also present a detailed analysis, using molecular line and dust continuum observations, of the region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm. Molecular line and millimeter continuum emission maps reveal the presence of six compact and luminous molecular clumps, with physical properties consistent with values found toward other massive star forming sources. This work includes the discovery of one of the most energetic and luminous molecular outflows known in the Galaxy, G331.512-0.103. For this high-speed outflow, I present ALMA observations that reveal a very compact, extremely young bipolar outflow and a more symmetric outflowing shocked shell surrounding a very small region of ionized gas. The source is one of the youngest examples of massive molecular outflows associated with the formation of a high-mass star.
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