The Antennae (22 Mpc) is one of the most well-known mergers in the nearby Universe. Its distance allow us to observe and study the gas at the scales of stellar cluster formation. It is an ideal source to understand how the galaxy dynamics in mergers trigger the formation of stars. Most of the stars in the Antennae are formed in compact and massive stellar clusters, dubbed super-star clusters (SSCs). The most massive (>106 M⊙) and youngest (<6 Myr) SSCs are located in the overlap region, where the two galaxies collide, and are associated with massive (several 108 M⊙) and super-giant (few hundred of pc) molecular complexes (SGMCs). The formation of SSCs must involve a complex interplay of merger-driven gas dynamics, turbulence fed by the galaxy interaction, and dissipation of the kinetic energy of the gas. Within SGMCs, a hierarchy of structures must be produced, including dense and compact concentrations of molecular gas massive enough to form SSCs, pre-cluster clouds (PCCs). For star formation to occur, the mechanical energy of PCCs must be radiated away to allow their self-gravity to locally win over their turbulent gas pressure. Specific tracers of turbulent dissipation are therefore key inputs to test the validity of this theoretical scenario. In my thesis, I studied the Antennae overlap region. My work is based on observations with the SINFONI spectro-imager at the VLT, which includes H2 rovibrational and Brγ line emission, and with ALMA, which includes the CO(3-2) line and dust continuum emission. Both data-sets have the needed sub-arcsecond angular resolution to resolve the scales of SSC formation. The spectral resolutions are enough to resolve motions within SGMCs. Combining CO and H2 line emission is key in my PhD work. I use CO as a tracer of the distribution and kinematics of the molecular gas, and H2 as a tracer of the rate at which the gas mechanical energy is dissipated.My thesis focuses on diverse sources in the Antennae overlap region which trace different stages of star formation: the gathering of mass necessary to form SGMCs, the formation of PCCs within SGMCs and the disruption of a parent cloud by a newly formed SSC. I show that at each stage turbulence plays a key role. I found that the kinetic energy of the galaxies is not thermalized in large scale shocks, it drives the turbulence in the molecular ISM at a much higher level than what is observed in the Milky Way. Near-IR spectral diagnostics show that, outside of SSCs embedded in their parent clouds, the H2 line emission is powered by shocks and traces the dissipation of the gas turbulent kinetic energy. I relate the H2 emission to the loss of kinetic energy required to form gravitationally bound clouds. This interpretation is supported by the discovery of a compact, bright H2 source not associated with any known SSC. It has the largest H2/CO emission ratio and is located where the data show the largest velocity gradient in the interaction region. To our knowledge, this is the first time that an extragalactic source with such characteristics is identified. We would be witnessing the formation of a cloud massive enough to form a SSC. The data also allow us to study the disruption of a parent molecular cloud by an embedded SSC. Its matter is loosely bound and its gravity would be supported by turbulence, which makes it easier for feedback to disrupt the parent cloud. I end my manuscript presenting two projects. I propose to establish additional energy dissipation tracers observable with ALMA, which gives us the high spatial and spectral resolution needed to isolate scales at which clusters form. This is a Cycle 1 proposal accepted in first priority. I also plan to expand my work to other nearby extragalactic sources by investigating the turbulence-driven formation of stars in different extragalactic sources by combining near-IR and submillimeter observations.

Using various molecular line and continuum emission criteria, we have selected a sample of six isolated, dense concentrations of molecular gas, i.e., “cores”, which are either starless (L694-2, L429, L1517B, and L1689-SMM16) or contain a protostellar Very Low Luminosity Object (VeLLO) and are currently experiencing gravitational collapse (L1014 and L1521F). Studying the molecular emission from dense gas tracers toward this sample of cores will help us gain a more detailed image of the internal physical conditions of dense cores and their evolution. We observed the cores in our sample in NH3 (1,1) and (2,2) emission using the Green Bank Telescope (GBT) and in N2H+ (1−0) emission using the Nobeyama Radio Observatory (NRO). L429 shows the most complicated structure among the cores in our sample. Also, the maxima of molecular line integrated intensities and dust continuum emission toward L429 show a significant offset. The rest of the cores in our sample are roughly round and the morphologies of line integrated intensities follow that of the corresponding continuum emission closely. Cores in our sample have gas kinetic temperatures ∼ 9 − 10 K and therefore show comparable thermal velocity dispersions. L429 and L1517B are, respectively, the most turbulent and most quiescent cores in our sample. Finally, L1521F is the most centrally concentrated core of our sample. L1689-SMM16 is the least previously studied core in our sample and had not yet been probed in molecular emission. Jeans and virial analyses made using updated measurements of core mass and size confirm that L1689-SMM16 is prestellar, i.e., gravitationally bound. It also has accumulated more mass compared to its corresponding Jeans mass in the absence of magnetic fields and therefore is a “super-Jeans” core. The high levels of X(NH3)/X(N2H+) and deuterium fractionation reinforce the idea that the core has not yet formed a protostar. Comparing the physical parameters of the core with those of a Bonnor-Ebert sphere reveals the advanced evolutionary stage of L1689-SMM16 and shows that it might be unstable to collapse. We do not detect any evidence of infall motions toward the core, however. Instead, red asymmetry in the line profiles of HCN (1−0) and HNC (1−0) indicates expansion of the outer layers of the core at a speed of ∼ 0.2 − 0.3 km s−1. For a gravitationally bound core, expansion in the outer layers might indicate that L1689-SMM16 is experiencing oscillations. Radiative transfer modelling of NH3 emission toward L694-2 and L1521F at low and high spatial resolutions show that the less evolved core, L694-2, is best described by relatively constant radial profiles of temperature and fractional NH3 abundance. On the other hand, L1521F, which contains a protostellar VeLLO, is best described by a radial abundance profile that is enhanced toward the core centre and a radial temperature profile that decreases toward the core centre. Comparison of our results with previous studies on L1544, a well-studied starless core, imply that as dense cores evolve and progress toward the moment of collapse, they become more centrally concentrated. As a result, the gas temperatures at their centres decrease, leading to increase in levels of CO depletion factor and increase in NH3 fractional abundance toward the centre. / Graduate

In this thesis I focus mainly in studying the process of star formation in both high redshift, and local star forming galaxies, by using an observational technique called integral field spectroscopy (IFS). Although these investigations are aimed at studying the star formation properties of these objects, throughout this work I will also discuss the geometric, kinematic, and chemical structures in the inter-stellar medium of these galaxies, which are intimately connected with the process of star formation itself. The studies presented here were conducted under the umbrella of two different projects. First, the HETDEX Pilot Survey for Emission Line Galaxies, where I have studied the properties of Ly-alpha emitting galaxies across the 2<z<4 range, with an emphasis in trying to understand the process by which Ly-alpha photons, produced in large quantities in the active star forming regions, are able to escape the ISM of these objects, allowing us to detect them in the Ly-alpha line. The second project from which results are presented here is the VIRUS-P Exploration of Nearby Galaxies (VENGA), an ongoing campaign to obtain spatially resolved spectroscopy over a broad wavelength range for large portions of the disks of 30 nearby spiral galaxies. In this thesis, the VENGA data is used to study the physical parameters that set the rate of star formation in the different environments present within galaxies in the local universe. / text

The clouds of gas and dust that constitute the Interstellar Medium (ISM) within the Milky Way and other galaxies can be studied through the spectral lines of the atoms and molecules. The ISM follows a lifecycle in which each of its phases can be traced through spectral lines in the Terahertz (THz) portion of the electromagnetic spectrum, loosely defined as 0.3 - 3 THz. Using the high spectral resolution afforded by heterodyne instruments, astronomers can potentially disentangle the large-scale structure and kinematics within these clouds. In order to study the ISM over large size scales, large format THz heterodyne arrays are needed. The research presented in this dissertation focuses on the development of two heterodyne array receiver systems for ISM studies, SuperCam and a Super-THz (>3 THz) receiver. SuperCam is a 64-pixel heterodyne imaging array designed for use on ground-based submillimeter telescopes to observe the astrophysically important CO J=3-2 emission line at 345 GHz. The SuperCam focal plane stacks eight, 1x8 mixer subarrays. Each pixel in the array has its own integrated superconductor-insulator-superconductor (SIS) mixer and Low Noise Amplifier (LNA). In spring 2012, SuperCam was installed on the University of Arizona Submillimeter Telescope (SMT) for its first engineering run with 32 active pixels. A second observing run in May 2013 had 52 active pixels. With the outliers removed, the median double sideband receiver temperature was 104 K. The Super-THz receiver is designed to observe the astrophysically important neutral atomic oxygen line at 4.7448 THz. The local oscillator is a third-order distributed feedback Quantum Cascade Laser operating in continuous wave mode at 4.741 THz. A quasi-optical hot electron bolometer is used as the mixer. We record a double sideband receiver noise temperature of 815 K, which is ~7 times the quantum noise limit and an Allan variance time of 15 seconds at an effective noise fluctuation bandwidth of 18 MHz. Heterodyne performance is confirmed by measuring a methanol line spectrum. By combining knowledge of large array formats from SuperCam and quasi-optical mixers, initial tests and designs are presented to expand the single pixel 4.7 THz receiver into a quasi-optical 16-pixel array.

I investigate the emission properties of the molecular interstellar medium in protoplanetary disks and galaxy mergers, though focus largely on the latter topic. I utilize both numerical models as well as observations to relate the emission characteristics to physical models for the formation and evolution of gas giant planets and galaxies. The main results of this thesis follow. (1) Gas giant protoplanets may be detectable via self-absorption signatures in molecular emission lines with sufficiently high critical density. Given the spatial resolution of e.g. ALMA, gas giant planets in formation may be directly imageable. (2) Starburst and AGN feedback-driven winds in galaxies can leave imprints on the molecular line emission properties via morphological outflows and high velocity peaks in the emission line spectra. Methods for distinguishing between high velocity peaks driven by dynamics versus those driven by winds are discussed. (3) CO line widths on average trace the virial velocity of z ∼ 6 quasar host halos. Thus, if the earliest quasars formed in ∼1013 M ⊙ halos, they are predicted to have broad molecular line widths. Selection effects may exist which tend quasars selected for optical luminosity toward molecular line widths narrower than the slightline-dependent mean. (4) Using the SMT, I observe a roughly linear relation between infrared luminosity and CO (J=3-2) luminosity in local galaxies confirming the results of recently observed L(IR)-HCN (J=1-0) relations. Subsequent modeling shows that observed SFR-molecular line luminosity relations owe to the average fraction of subthermally excited gas in galaxies, and are simply reflective of the assumed Schmidt law governing the SFR.

Moving groups are associations of stars which originated from the same star forming region. These groups are typically young (< 200 Myr) since they have not dissipated into the galactic field population. Over the last 15 years, roughly 10 such moving groups have been found with distances < 150 pc (7 with distances < 100 pc), each with a unique velocity and position. This work first investigates the likelihood to resolve star from two moving groups (AB Doradus and Beta Pictoris) using high spacial resolution optical interferrometry and found 5 AB Doradus stars and 1 Beta Pictoris star with declinations > -30 could be spacially resolved. To more deeply characterize individual groups, we used the 2.7m telescope at the McDonald Observatory to observe 10 proposed AB Doradus stars and 5 proposed Octans-Near stars (3 probable members, 2 possible) with high resolution (R ~60,000) optical spectroscopy. Each group is characterized in three ways: (1) Chemical analysis to determine the homogeneity among members, (2) Kinematic traceback to determine the origin, and (3) Isochrone fitting to determine the age. We find the 8 stars in our AB Doradus sample are chemically homogeneous with [M/H] = -0.03 ± 0.06 dex, traceback to an age of 125 Myr, and the stars in this mass range are on the main sequence. The two deviants are a metal rich, potentially younger member and a metal poor, young star likely not associated with AB Doradus. In our Octans-Near sample, we find the 3 probable members have [M/H] = -0.06 ± 0.11, the stars do not trace back to a common origin, and the probable members are on the main sequence. In addition to these tests, we found that the probable members are slightly more lithium depleted than the Pleiades, implying an age between 125 and 200 Myr. Finally, we investigate systematic trends in fundamental stellar parameters from the use of different techniques. Preliminary results find differences in temperatures between interferrometric and spectroscopic techniques to be a function of temperature with a interferrometric temperatures being cooler by an average of 36 ± 115 K. We also calculated the chemical abundances as a function of condensation temperature for our moving group sample and predict 2 stars in AB Doradus could represent the initial star forming environment and discuss the implications for planet hosting stars in nearby moving groups. This updated characterization technique allows for a deeper understanding of the moving group environment. As future, high precision instruments emerge in astronomy (Jame Webb Space Telescope, GAIA, 30m class telescopes), moving groups are ideal targets since these associations will help us understand star forming regions, stellar evolution at young ages, constrain stellar evolutionary models, and identify planetary formation and evolution mechanisms.

The construction of the James Webb Space Telescope has brought attention to infrared astronomy and cosmology. The potential information about our universe to be gained by this mission and future infrared telescopes is staggering, but infrared observation faces many obstacles. These telescopes face large amounts of noise by many phenomena, from emission off of the mirrors to the cosmic infrared background. Infrared telescopes need to be designed in such a way that noise is minimized to achieve sufficient signal to noise ratio on high redshift objects. We will investigate current and planned space and ground based telescopes, model the noise they encounter, and discover their limitations. The ultimate goal of our investigation is to compare the sensitivity of these missions in the near and mid IR and to propose new missions. Our investigation is broken down into four major sections: current missions, noise, signal, and proposed missions. In the proposed missions section we investigate historical and current infrared telescopes with attention given to their location and properties. The noise section discusses the noise that an infrared telescope will encounter and set the background limit. The signal section will look at the spectral energy distributions (SED) of a few significant objects in our universe. We will calculate the intensity of the objects at various points on Earth and in orbit. In the final section we use our findings in the signal and noise sections to model integration times (observation time) for a variety of missions to achieve a given signal to noise ratio (SNR).

A two dimensional hydrodynamic model describing the solar wind interaction with the local interstellar medium, which surrounds the solar system, is used to study the heliosphere both as a steady-state- and dynamic structure. The finite volume method used to solve the associated system of hydrodynamic equations numerically is discussed in detail. Subsequently the steady state heliosphere is studied for both the case where the solar wind and the interstellar medium are assumed to consist of protons only, as well as the case where the neutral hydrogen population in the interstellar medium is taken into account. It is shown that the heliosphere forms as three waves, propagating away from the initial point of contact between the solar wind and interstellar matter, become stationary. Two of these waves become stationary at sonic points, forming the termination shock and bow shock respectively. The third wave becomes stationary as a contact discontinuity, called the heliopause. It is shown that the position and geometry of the termination shock, heliopause and bow shock as well as the plasma flow characteristics of the heliosphere largely depend on the dynamic pressure of either the solar wind or interstellar matter. The heliosphere is modelled as a dynamic structure, including both the effects of the solar cycle and short term variations in the solar wind observed by a range of spacecraft over the past ~ 30 years. The dynamic model allows the calculation of an accurate record of the heliosphere state over the past ~ 30 years. This record is used to predict the time at which the Voyager 2 spacecraft will cross the termination shock. Voyager 1 observations of 10 MeV cosmic ray electrons are then used in conjunction with a cosmic ray modulation model to constrain the record of the heliosphere further. It is shown that the dynamic hydrodynamic model describes the heliosphere accurately within a margin of error of ±0.7 years and ±3 AU. The model predicts that Voyager 2 crossed the termination shock in 2007, corresponding to preliminary results from observations indicating that the crossing occurred in August 2007. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.

This document describes studies of two independent regions of the interstellar medium (ISM). These studies have the common element that both pertain to regions in our Galaxy that are known to be associated with present-day star formation. These studies aim to help us understand the ISM, star formation, and ultimately where we came from, since, after all, our star, the Sun, is itself the product of star formation 4.5 billion years ago. The first project measured the Zeeman Effect on the 21 cm H I absorption line in order to create a map of the line of sight magnetic fields near a star forming region called W3. From the map of the field, it was possible to create a three dimensional model of the magnetic field morphology. Also, calculating the various energies associated with W3 revealed that it is most likely in virial equilibrium, not expanding or contracting. The second project used an instrument on the Hubble Space Telescope (HST) to measure the abundance of iron in a neutral region near the Orion Nebula called Orion’s Veil. One of the goals of this project is to investigate whether solid dust grains can be destroyed by ionizing radiation by comparing the amount of solid iron in Orion’s Veil to the amount in the nearby ionized regions. By measuring the depletion of iron in the neutral Veil and comparing it to the depletion of iron the H+ regions of the Orion Nebula, it was possible to conclude that iron was not being released into the gas phase by ultraviolet photons. In addition, oscillator strengths for two Fe II transitions were measured.

RR Lyrae stars are old, iron-poor, Helium-burning variable stars. RR Lyraes are extremely useful for tracing phase-space structures and metallicities within the galaxy because they are easy to identify, have consistent luminosities, and are found in large numbers in the galactic disk, bulge, and halo. Here we present a new set of spectroscopic metallicity calibrations that use the equivalent widths of the Ca II K, Hγ, and Hδ lines to calculate metallicity values. Applied to spectroscopic survey data, these calibrations will help shed light on the evolution of the Milky Way and other galaxies.