This thesis aims to improve our understanding of the early stages of massive star formation and of the physical properties of interstellar clouds. To achieve this, I have used submillimeter continuum dust emission data obtained by the Balloon-borne Large Aperture submillimeter Telescope (BLAST) in the first science flight in 2005, with a 2-m telescope operating simultaneously at 250, 350, and 500 micron. Unfortunately, BLAST produced images of about 3'3 resolution due to an uncharacterized optical problem. In Chapter~2, I discuss implementation of the Lucy-Richardson (L-R) method of deconvolution to restore BLAST images to near diffraction limited resolution. Its performance and convergence have been extensively analyzed through simulations and comparison of deconvolved images with available high-resolution maps. In Chapter~3, I study diverse phenomena in the Cygnus~X region associated with high mass star-formation. To interpret the BLAST emission more fully and place the compact sources in context, archival data cubes of 13CO line emission from KOSMA, MIPS images from the Spitzer Legacy Survey of this region, and 21-cm radio continuum emission from the Canadian Galactic Plane Survey have been used. Utilizing available ancillary multi-wavelength observations, the influence of OB stars and stellar clusters on Cygnus~X has been studied,revisiting the well-known DR HII regions and their surroundings in the light of submillimeter continuum dust emission and CO line emission. An effort has been made to assess the evolutionary sequence of the compact sources (spatial extent of about 1~pc) on the basis of L-M diagram and subsequently to relate this sequence to independent empirical evidence and theory. Using multi-resolution observations, evidence for hierarchical substructures within molecular clouds has been examined. Finally, in Chapter~4, a multi-wavelength power spectrum analysis of the large scale brightness fluctuations in the Galactic plane is presented. This analysis has been used to assess the level of cirrus noise which limits the detection of faint sources. A characteristic power law exponent of about -2.7 has been obtained for sub-regions of Aquila and Cygnus~X. The observed relative amplitudes of power spectra at different wavelengths have been related through a spectral energy distribution, thereby determining a characteristic temperature for the Galactic diffuse emission.

The lifetime of a Giant Molecular Cloud (GMC) and the total mass of stars that form within it are crucial to the understanding of star formation rates across a whole galaxy. In particular, the stars within a GMC may dictate its disruption and the quenching of further star formation. Indeed, observations show that the Milky Way contains GMCs with extensive expanding bubbles while the most massive stars are still alive. Simulating entire GMCs is challenging, due to the large variety of physics that needs to be included, and the computational power required to accurately simulate a GMC over tens of millions of years. Using the radiative-magneto-hydrodynamic code Enzo, I have run many simulations of GMCs. I obtain robust results for the fraction of gas converted into stars and the lifetimes of the GMCs: (A) In simulations with no stellar outputs (or ``feedback''), clusters form at a rate of 30% of GMC mass per free fall time; the GMCs were not disrupted but contained forming stars. (B) Including ionization gas pressure or radiation pressure into the simulations, both separately and together, the star formation was quenched at between 5% and 21% of the original GMC mass. The clouds were fully disrupted within two dynamical times after the first cluster formed. The radiation pressure contributed the most to the disruption of the GMC and fully quenched star formation even without ionization. (C) Simulations that included supernovae showed that they are not dynamically important to GMC disruption and have only minor effects on subsequent star formation. (D) The inclusion of a few micro Gauss magnetic field across the cloud slightly reduced the star formation rate but accelerated GMC disruption by reducing bubble shell disruption and leaking. These simulations show that new born stars quench further star formation and completely disrupt the parent GMC. The low star formation rate and the short lifetimes of GMCs shown here can explain the low star formation rate across the whole galaxy.

This thesis aims to improve our understanding of the early stages of massive star formation and of the physical properties of interstellar clouds. To achieve this, I have used submillimeter continuum dust emission data obtained by the Balloon-borne Large Aperture submillimeter Telescope (BLAST) in the first science flight in 2005, with a 2-m telescope operating simultaneously at 250, 350, and 500 micron. Unfortunately, BLAST produced images of about 3'3 resolution due to an uncharacterized optical problem. In Chapter~2, I discuss implementation of the Lucy-Richardson (L-R) method of deconvolution to restore BLAST images to near diffraction limited resolution. Its performance and convergence have been extensively analyzed through simulations and comparison of deconvolved images with available high-resolution maps. In Chapter~3, I study diverse phenomena in the Cygnus~X region associated with high mass star-formation. To interpret the BLAST emission more fully and place the compact sources in context, archival data cubes of 13CO line emission from KOSMA, MIPS images from the Spitzer Legacy Survey of this region, and 21-cm radio continuum emission from the Canadian Galactic Plane Survey have been used. Utilizing available ancillary multi-wavelength observations, the influence of OB stars and stellar clusters on Cygnus~X has been studied,revisiting the well-known DR HII regions and their surroundings in the light of submillimeter continuum dust emission and CO line emission. An effort has been made to assess the evolutionary sequence of the compact sources (spatial extent of about 1~pc) on the basis of L-M diagram and subsequently to relate this sequence to independent empirical evidence and theory. Using multi-resolution observations, evidence for hierarchical substructures within molecular clouds has been examined. Finally, in Chapter~4, a multi-wavelength power spectrum analysis of the large scale brightness fluctuations in the Galactic plane is presented. This analysis has been used to assess the level of cirrus noise which limits the detection of faint sources. A characteristic power law exponent of about -2.7 has been obtained for sub-regions of Aquila and Cygnus~X. The observed relative amplitudes of power spectra at different wavelengths have been related through a spectral energy distribution, thereby determining a characteristic temperature for the Galactic diffuse emission.

The lifetime of a Giant Molecular Cloud (GMC) and the total mass of stars that form within it are crucial to the understanding of star formation rates across a whole galaxy. In particular, the stars within a GMC may dictate its disruption and the quenching of further star formation. Indeed, observations show that the Milky Way contains GMCs with extensive expanding bubbles while the most massive stars are still alive. Simulating entire GMCs is challenging, due to the large variety of physics that needs to be included, and the computational power required to accurately simulate a GMC over tens of millions of years. Using the radiative-magneto-hydrodynamic code Enzo, I have run many simulations of GMCs. I obtain robust results for the fraction of gas converted into stars and the lifetimes of the GMCs: (A) In simulations with no stellar outputs (or ``feedback''), clusters form at a rate of 30% of GMC mass per free fall time; the GMCs were not disrupted but contained forming stars. (B) Including ionization gas pressure or radiation pressure into the simulations, both separately and together, the star formation was quenched at between 5% and 21% of the original GMC mass. The clouds were fully disrupted within two dynamical times after the first cluster formed. The radiation pressure contributed the most to the disruption of the GMC and fully quenched star formation even without ionization. (C) Simulations that included supernovae showed that they are not dynamically important to GMC disruption and have only minor effects on subsequent star formation. (D) The inclusion of a few micro Gauss magnetic field across the cloud slightly reduced the star formation rate but accelerated GMC disruption by reducing bubble shell disruption and leaking. These simulations show that new born stars quench further star formation and completely disrupt the parent GMC. The low star formation rate and the short lifetimes of GMCs shown here can explain the low star formation rate across the whole galaxy.

We have studied the properties of molecular clouds and the stellar population associated with 10 H II regions. We used the James Clerk Maxwell Telescope (JCMT) to make 12CO(2-1) maps in order to study the structure of the cloud and to identify the dense clumps within the cloud. In half of our sources we found that molecular gas appears to have been pushed and compressed into the shells around the expanding ionized gas and fragmented into clumps. Most of these clumps have higher temperature and density compared to the other clumps within the mapped regions. We made pointed observations in 13CO(2-1) and CS(5-4) at the peak of 12CO(2-1) within each clump to measure and calculate the physical properties of the clumps such as line width, excitation temperature, density and mass. Two gas components were selected in the cloud associated with S175 to investigate the influence of the H II region on the molecular gas: S175A is adjacent to the ionization fronts and probably affected by the expanding H II region while S175B is too distant to be affected. Contrary to our expectation S175B was a turbulent region with broadened line profiles. We made a sub-map in 12CO(3-2) using HARP at the JCMT to search for the source of turbulence and identified a proto-stellar outflow in S175B. We examined the relationship between gas parameters derived for the clumps within the entire sample. The identified clumps were found to be divided into two categories: “type I” sources in which we can find a relationship between size and line width and “type II” sources where there is no relation. We found that the power law indices for type I sources are generally larger than the previous studies. Larger line widths and consequently larger indices seems to be an initial environmental characteristic of massive star forming regions We found that mass and column density increase with line width for both type I and type II sources. We did not find any relation between the size and column density. The influence of the H II region on temperature and line widths was examined and we found that the temperature decreases with distance from the ionized fronts but no change was found for the line width. Although most of the clumps within the compressed shells around the H II region have generally larger line widths, from this test we may conclude that the internal dynamics of the cloud beyond the compressed shells is not much influenced by the expanding H II region. Finally, our near IR study of the stellar populations using 2MASS data, shows that in half of the regions the exciting star belongs to a cluster. We also found that star formation is consistent with triggering by the expansion of the ionized gas in some of sources in our sample. At least two young embedded clusters have been identified at the same position as the dense clumps within fragmented shells around H II regions. These clumps have high temperature and density and large line widths. We identify some other hot and dense clumps very similar in molecular gas properties as candidates of cluster or massive star formation. Most of the active star forming regions associated with H II regions have a population of massive newborn stars compared to a star forming cloud which is distant from the massive star and the ionized gas. We conclude that more massive stars form in the molecular cloud at the peripheries of H II regions but it is not clear f this is a result of the initial conditions that have formed the massive, exciting star of the H II region or a feedback of the massive star itself and the expanding H II region.

We have studied the properties of molecular clouds and the stellar population associated with 10 H II regions. We used the James Clerk Maxwell Telescope (JCMT) to make 12CO(2-1) maps in order to study the structure of the cloud and to identify the dense clumps within the cloud. In half of our sources we found that molecular gas appears to have been pushed and compressed into the shells around the expanding ionized gas and fragmented into clumps. Most of these clumps have higher temperature and density compared to the other clumps within the mapped regions. We made pointed observations in 13CO(2-1) and CS(5-4) at the peak of 12CO(2-1) within each clump to measure and calculate the physical properties of the clumps such as line width, excitation temperature, density and mass. Two gas components were selected in the cloud associated with S175 to investigate the influence of the H II region on the molecular gas: S175A is adjacent to the ionization fronts and probably affected by the expanding H II region while S175B is too distant to be affected. Contrary to our expectation S175B was a turbulent region with broadened line profiles. We made a sub-map in 12CO(3-2) using HARP at the JCMT to search for the source of turbulence and identified a proto-stellar outflow in S175B. We examined the relationship between gas parameters derived for the clumps within the entire sample. The identified clumps were found to be divided into two categories: “type I” sources in which we can find a relationship between size and line width and “type II” sources where there is no relation. We found that the power law indices for type I sources are generally larger than the previous studies. Larger line widths and consequently larger indices seems to be an initial environmental characteristic of massive star forming regions We found that mass and column density increase with line width for both type I and type II sources. We did not find any relation between the size and column density. The influence of the H II region on temperature and line widths was examined and we found that the temperature decreases with distance from the ionized fronts but no change was found for the line width. Although most of the clumps within the compressed shells around the H II region have generally larger line widths, from this test we may conclude that the internal dynamics of the cloud beyond the compressed shells is not much influenced by the expanding H II region. Finally, our near IR study of the stellar populations using 2MASS data, shows that in half of the regions the exciting star belongs to a cluster. We also found that star formation is consistent with triggering by the expansion of the ionized gas in some of sources in our sample. At least two young embedded clusters have been identified at the same position as the dense clumps within fragmented shells around H II regions. These clumps have high temperature and density and large line widths. We identify some other hot and dense clumps very similar in molecular gas properties as candidates of cluster or massive star formation. Most of the active star forming regions associated with H II regions have a population of massive newborn stars compared to a star forming cloud which is distant from the massive star and the ionized gas. We conclude that more massive stars form in the molecular cloud at the peripheries of H II regions but it is not clear f this is a result of the initial conditions that have formed the massive, exciting star of the H II region or a feedback of the massive star itself and the expanding H II region.

There has been many recent observations in the area of star formation. High-resolution observations of other galaxies enabled a study of extragalactic star formation in more detailed while large scale surveys of the Milky Way enabled a more comprehensive study of Galactic star formation. The main goal of this thesis is to use multi-wavelength, large-scale observations of the Milky Way to connect Galactic to extragalactic star formation and to study star formation regulation in molecular clouds. We tested the use of extragalactic star formation rate tracers on nearby molecular clouds and found that the total infrared and 24 μm luminosity underestimate star formation rates of nearby molecular clouds by a large factor, indicating a problem of using extragalactic tracers of star formation on small regions and regions with low mass or low star formation rates. We studied the relation between star formation and molecular gas distribution in a 11 square degree of the Galactic Plane on various spatial scales starting from a clump scale of around few parsecs to a scale of ≈ 200 parsec. The result shows a good correlation between molecular gas and star formation on a scale above ≈ 5 − 8′. The star formation relation that is seen on disk-averaged scales in other galaxies shows a large scatter on the small scales. We built a catalog of Galactic molecular clouds with measured star formation rates and studied the relations between properties of molecular clouds and star formation. We tested several models of star formation on the catalog of molecular clouds. We found that the dense gas mass shows significant correlations with star formation rates but the depletion time of dense gas varies with other properties of the clouds. We found that the free- fall efficiency is higher in dense gas compared to the general molecular gas of the clouds.

Stars form from collapsing massive clouds of gas and dust. The UV and optical light emitted by a forming or recently-formed star is absorbed by the surrounding cloud and is re-radiated thermally at infrared and submillimetre wavelengths. Observations in the submillimetre spectrum are uniquely sensitive to star formation in the early Universe, as the peak of the thermal emission is redshifted to submillimetre wavelengths. The coolest objects in star forming regions in our own Galaxy, including heavily-obscured proto-stars and starless gravitationally-bound clumps, are also uniquely bright in the submillimetre spectrum. The Earth's atmosphere is mostly opaque at these wavelengths, however, limiting the spectral coverage and sensitivity achievable from ground-based observatories. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) observes the sky from an altitude of 40 km, above 99.5% of the atmosphere, using a long-duration scientific balloon platform. BLAST observes at 3 broad-band wavelengths spanning 250-500 micron, taking advantage of detector technology developed for the space-based instrument SPIRE, scheduled for launch in 2008. The greatly-enhanced atmospheric transmission at float altitudes, increased detector sensitivity and large number of detector elements allow BLAST to survey much larger fields in a much smaller time than can be accomplished with ground-based instruments. It is expected that in a single 10-day flight, BLAST will detect ~10000 extragalactic sources, ~100 times the number detected in 10 years of ground-based observations, and 1000s of Galactic star-forming sources, a large fraction of which are not seen by infrared telescopes. The instrument has performed 2 scientific flights, in the summer of 2005 and winter of 2006, for a total of 16 days of observing time. This thesis discusses the design of the instrument, performance of the flights, and presents the analysis of 2 of the fields observed during the first flight. A failure in the optical system during the first flight precluded sensitive extragalactic observations, so the majority of the flight was spent observing Galactic targets. We anticipate exciting extragalactic and Galactic results from the 2006 data.

Stars form from collapsing massive clouds of gas and dust. The UV and optical light emitted by a forming or recently-formed star is absorbed by the surrounding cloud and is re-radiated thermally at infrared and submillimetre wavelengths. Observations in the submillimetre spectrum are uniquely sensitive to star formation in the early Universe, as the peak of the thermal emission is redshifted to submillimetre wavelengths. The coolest objects in star forming regions in our own Galaxy, including heavily-obscured proto-stars and starless gravitationally-bound clumps, are also uniquely bright in the submillimetre spectrum. The Earth's atmosphere is mostly opaque at these wavelengths, however, limiting the spectral coverage and sensitivity achievable from ground-based observatories. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) observes the sky from an altitude of 40 km, above 99.5% of the atmosphere, using a long-duration scientific balloon platform. BLAST observes at 3 broad-band wavelengths spanning 250-500 micron, taking advantage of detector technology developed for the space-based instrument SPIRE, scheduled for launch in 2008. The greatly-enhanced atmospheric transmission at float altitudes, increased detector sensitivity and large number of detector elements allow BLAST to survey much larger fields in a much smaller time than can be accomplished with ground-based instruments. It is expected that in a single 10-day flight, BLAST will detect ~10000 extragalactic sources, ~100 times the number detected in 10 years of ground-based observations, and 1000s of Galactic star-forming sources, a large fraction of which are not seen by infrared telescopes. The instrument has performed 2 scientific flights, in the summer of 2005 and winter of 2006, for a total of 16 days of observing time. This thesis discusses the design of the instrument, performance of the flights, and presents the analysis of 2 of the fields observed during the first flight. A failure in the optical system during the first flight precluded sensitive extragalactic observations, so the majority of the flight was spent observing Galactic targets. We anticipate exciting extragalactic and Galactic results from the 2006 data. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Star cluster formation involves the conversion of molecular gas into stars inside giant molecular clouds (GMCs). Such a process involves many dynamical evolution mechanisms, including mergers between smaller star clusters (subclusters) on which we focus in this thesis. We take results of simulations performed by Howard et al. 2018 (H18) which found that young massive cluster (YMC) formation is heavily dependant on the process of subcluster mergers, and we simulate said mergers at higher resolution. Subclusters inside such GMC simulations are modelled using the sink particle prescription which does not resolve individual star particles or gas parcels inside the subcluster they represent. We employ a more controlled method in simulating subcluster mergers to better understand the response of the stellar and gas components of a subcluster from the merger process. To do this, we take the parameters of the sink particles created in H18 and set up spheres of stars and gas. We use the AMUSE framework to couple the N-body evolution of the stars to the smoothed particle hydrodynamics (SPH) evolution of the gas such that both components of a given cluster can realistically react to each other. We model 15 of these mergers and find that once the velocity at which the two clusters collide (collisional velocity) exceeds $\approx 10$kms$^{-1}$, the resultant cluster is not monolithic (i.e. it still contains two separate stellar components) while all other simulations merge into one monolithic stellar and gas component cluster. We also find that, regardless of the collisional velocity of masses of the component clusters, all resultant clusters lose a fraction of their stellar and gas mass. This fraction is directly proportional to the collisional velocity and is a discrepancy between the sink particle prescription (where all mass is contained inside a constant sink particle accretion radius) and real cluster mergers. A further discrepancy we find is that all simulations result in a cluster whose outermost regions are expanding and that the rate of this expansion is somewhat proportional to the collisional velocity of the merger. These results point to the inaccuracy of the sink particle prescription and allow us to develop tools to improve on it in future simulations. Next, we fit commonly used analytical density profiles to both the stellar and gas component of our resultant clusters and find that, while they do not provide particularly excellent fits, they provide constraints on what is an acceptable fit. Lastly, we analyze the amount by which gas with potentially star forming densities increase due to the merger and we find that all mergers increase their star forming gas mass fraction by roughly 50 per cent implying that mergers may be an effective tool for triggering star formation. / Thesis / Master of Science (MSc)