No description available.

Astronomers require large amounts of spectroscopic data for faint astronomical sources if they are to successfully confront today's most important cosmological and astrophysica1 problems. However, until recently such data has been particularly difficult to acquire and the supply of telescope time available has fallen well short of demand. This thesis describes spectroscopic techniques of high efficiency that allow the data to be obtained using a minimum of telescope time. The technical aspects discussed include instrumentation, observing practices and data reduction. In particular, a new faint object spectrograph for the La Palma Observatory and an automated multi-fibre spectrograph coupler for the Anglo-Australian Telescope are described. It is now feasible for extensive spectroscopic surveys to be carried out at very faint magnitudes.

The gaseous halo surrounding a galaxy disk is often referred to as the circum-galactic medium (CGM). The boundary of the CGM is loosely defined as the virial radius of the galaxy. Recent observations and simulations have shown that the CGM is massive, multiphase, clumpy, and metal-enriched. The CGM plays an important role in galaxy formation and evolution – it serves as a massive baryonic reservoir, from which the disk accretes gas fuel to sustain the star-formation activities, and to which the disk deposits feedback material. This dissertation focuses on the gas distribution in the CGM of the Milky Way (MW) and the baryon cycle between the CGM and disk of our neighbor – the Triangulum Galaxy (M33). Observations of the MW’s CGM are unavoidably contaminated by foreground gas since we reside in the MW’s disk. Conventionally, a velocity cut at |VLSR|~100 km/s is used as a proxy for distance, with low-velocity (|VLSR|<100 km/s) gas being more nearby to the Galactic disk than high-velocity gas. Using both a MW-mass simulation and all-sky QSO observations, I show that the low-velocity gas in the MW’s CGM is as massive as their high-velocity counterpart, and that the MW most likely hosts a massive CGM reservoir as those L~L* galaxies at z~0.2. I further study how baryons are cycled between the disk and CGM by observing gas accretion in M33. Using HST/COS to observe seven UV-bright stars in M33’s disk, I find that there is a layer of metal-enriched inflow moving towards M33 at a rate of dM/dt=2.9 Msun/yr. The gas inflow may be related to galactic fountain process or debris falling back down due to the potential past M31-M33 interaction. This work is among the first to unambiguously reveal the existence of a disk-wide, ionized galactic inflow beyond the Milky Way. In addition, with the same set of HST/COS sightlines, I make a serendipitous discovery of an ionized very-high-velocity cloud towards M33.

No description available.

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.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 201-212).

Thesis (Ph. D.)--University of Chicago, Department of Astronomy and Astrophysics, June 2001. / Includes bibliographical references. Also available on the Internet.

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.

No description available.

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.