We present the results of an optical spectroscopic survey of 46 heavily obscured quasar candidates. Objects are selected using their mid-infrared (mid-IR) colours and magnitudes from the Wide-Field Infrared Survey Explorer (WISE) anzd their optical magnitudes from the Sloan Digital Sky Survey. Candidate Active Galactic Nuclei (AGNs) are selected to have mid-IR colours indicative of quasar activity and lie in a region of mid-IR colour space outside previously published X-ray based selection regions. We obtain optical spectra for our sample using the Robert Stobie Spectrograph on the Southern African Large Telescope. 30 objects (65 per cent) have identifiable emission lines, allowing for the determination of spectroscopic redshifts. Other than one object at z similar to 2.6, candidates have moderate redshifts ranging from z = 0.1 to 0.8 with a median of 0.3. 21 (70 per cent) of our objects with identified redshift (46 per cent of the whole sample) are identified as AGNs through common optical diagnostics. We model the spectral energy distributions of our sample and found that all require a strong AGN component, with an average intrinsic AGN fraction at 8 mu m of 0.91. Additionally, the fits require large extinction coefficients with an average E(B - V)(AGN) = 17.8 (average A(V)(AGN) = 53.4). By focusing on the area outside traditional mid-IR photometric cuts, we are able to capture and characterize a population of deeply buried quasars that were previously unattainable through X-ray surveys alone.

We present the first discoveries from a survey of z greater than or similar to 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg(2) of sky down to z(AB) similar to 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < + 60 degrees, reaching J(VEGA) similar to 19.6 (5-sigma). The combination of these data sets allows us to discover quasars at redshift z greater than or similar to 7 and to conduct a complete census of the faint quasar population at z greater than or similar to 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z greater than or similar to 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z similar to 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 angstrom being M-1450 = -25.83 and M-1450 = -25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z greater than or similar to 6. The new z = 6.63 quasar has an absolute magnitude of M-1450 = -25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z greater than or similar to 7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield similar to 200 z similar to 6 quasars to z(AB) < 21.5, similar to 1000 z similar to 6 quasars to z(AB) < 23, and similar to 30 quasars at z > 6.5 to J(VEGA) < 19.5.

SDSS J163459.82+204936.0 is a local (z = 0.1293) infrared-luminous quasar with L-IR = 10(11.91) L-circle dot. We present a detailed multiwavelength study of both the host galaxy and the nucleus. The host galaxy, appearing as an early-type galaxy in the optical images and spectra, demonstrates violent, obscured star formation activities with SFR approximate to 140 M-circle dot yr(-1), estimated from either the polycyclic aromatic hydrocarbon emission or IR luminosity. The optical to NIR spectra exhibit a blueshifted narrow cuspy component in H beta, He I lambda lambda 5876, 10830, and other emission lines consistently with an offset velocity of approximate to 900 km s(-1), as well as additional blueshifting phenomena in high-ionization lines (e.g., a blueshifted broad component of He I lambda 10830 and the bulk blueshifting of [O III].5007), while there exist blueshifted broad absorption lines (BALs) in Na I. D and He I lambda lambda 3889, 10830, indicative of the active galactic nucleus outflows producing BALs and emission lines. Constrained mutually by the several BALs in the photoionization simulations with Cloudy, the physical properties of the absorption line outflow are derived as follows: density 10(4) < n(H) less than or similar to 10(5) cm(-3), ionization parameter 10(-1.3) less than or similar to U 10(-0.7), and column density 10(22.5) less than or similar to N-H less than or similar to 10(22.9) cm(-2), which are similar to those derived for the emission line outflows. This similarity suggests a common origin. Taking advantages of both the absorption lines and outflowing emission lines, we find that the outflow gas is located at a distance of similar to 48-65 pc from the nucleus and that the kinetic luminosity of the outflow is 10(44)-10(46) erg s(-1). J1634+2049 has a off-centered galactic ring on the scale of similar to 30. kpc that is proved to be formed by a recent head-on collision by a nearby galaxy for which we spectroscopically measure the redshift. Thus, this quasar is a valuable object in the transitional phase emerging out of dust enshrouding as depicted by the coevolution scenario invoking galaxy merger (or violent interaction) and quasar feedback. Its proximity enables our further observational investigations in detail (or tests) of the co-evolution paradigm.

We report on the diversity in quasar spectra from the Baryon Oscillation Spectroscopic Survey. After filtering the spectra to mitigate selection effects and Malmquist bias associated with a nearly flux-limited sample, we create high signal-to-noise ratio composite spectra from 58,656 quasars (2.1 <= z <= 3.5), binned by luminosity, spectral index, and redshift. With these composite spectra, we confirm the traditional Baldwin effect (BE, i. e., the anticorrelation of C IV equivalent width ( EW) and luminosity) that follows the relation W-lambda alpha L-beta w with slope beta(w) = -0.35 +/- 0.004, -0.35 +/- 0.005, and -0.41 +/- 0.005 for z. =. 2.25, 2.46, and 2.84, respectively. In addition to the redshift evolution in the slope of the BE, we find redshift evolution in average quasar spectral features at fixed luminosity. The spectroscopic signature of the redshift evolution is correlated at 98% with the signature of varying luminosity, indicating that they arise from the same physical mechanism. At a fixed luminosity, the average C IV FWHM decreases with increasing redshift and is anti-correlated with C IV EW. The spectroscopic signature associated with C IV FWHM suggests that the trends in luminosity and redshift are likely caused by a superposition of effects that are related to black hole mass and Eddington ratio. The redshift evolution is the consequence of a changing balance between these two quantities as quasars evolve toward a population with lower typical accretion rates at a given black hole mass.

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.

This dissertation examines two broad topics -- emission line properties of active galactic nuclei (AGN) and the effect of hands-on, integrated science courses on student understanding of astronomy. To investigate trends in overall properties of emission lines in AGN, we apply principal component analysis (PCA) to the fluxes in the H [beta] - (O III) region of a sample of 9046 spectroscopically-identified broad-line AGN from the Sloan Digital Sky Survey (SDSS) Data Release 5 with a redshift range of 0.1 < z < 0.56. After performing independent spectral PCA on subsets defined effectively by their (O III) equivalent width (EW), we find only the weakest (O III) objects retain the optical Fe II - (O III) anticorrelation and the correlation of EW[subscript O III] with H [beta] linewidth that have previously been found in high-luminosity AGN. The objects with strongest EW[subscript O III] do not differ from the entire data set significantly in other spectral and derived properties, such as luminosity, redshift, emission line shapes, Eddington ratio, continuum slope, and radio properties. However, our findings are consistent with previous suggestions that (O III) emission is primarily a function of covering factor of the narrow-line region. To investigate the other side of the Fe II - (O III) anticorrelation, we examine the effect of changes in the gas-phase abundance of Fe on observed variation in Fe II. Using AGN spectra from the SDSS in the redshift range of 0.2 < z < 0.35, we measure the Fe/Ne abundance of the narrow-line region (NLR) using the (Fe VII)/(Ne V) line intensity ratio. We find no significant difference in the abundance of Fe relative to Ne in the NLR as a function of Fe II/H [beta]. However, the (N II)/(S II) ratio increases by a factor of 2 with increasing Fe II strength. This indicates a trend in N/S abundance ratio, and by implication in the overall metallicity of the NLR gas, with increasing Fe II strength. We propose that the wide range of Fe II strength in AGN largely results from the selective depletion of Fe into grains in the low ionization portion of the broad-line region. We utilize photoionization models to show that the strength of the optical Fe II lines varies almost linearly with gas-phase Fe abundance, while the ultraviolet Fe II strength varies more weakly, as seen observationally. After examining the emission line properties of large samples of fairly typical AGN, we investigated the newly expanded regime of low-mass AGN (M[subscript BH] [less than or approximately equal to] 10⁶ M[subscript sun]) with respect to their emission line properties at a smaller scale. We utilize the high spectral resolution and small aperture of our Keck data of 27 low-mass AGN, taken with the Echellette Spectrograph and Imager, to isolate the NLRs of these low-mass black holes. Some of these low-luminosity objects plausibly represent examples of the low-metallicity AGN described by Groves et al. (2006), based on their (N II)/H[alpha] ratios and their consistency with the Kewley & Ellison (2008) mass-metallicity relation. We also find that these low-mass AGN have steeper UV continuum slopes than more-massive AGN based on their He II/H[beta] ratio. Overall, NLR emission lines in these low-mass AGN exhibit trends similar to those seen in AGN with higher-mass BHs, such as increasing blueshifts and broadening with increasing ionization potential. Additionally, we see evidence of an intermediate line region whose intensity correlates with L/L[subscript Edd] in these objects, as seen in higher-mass AGN. We highlight the interesting trend that, at least in these low-mass BHs, the (O III) EW is highest in symmetric NLR lines with no blue wing. This trend of increasing (O III) EW with line symmetry could be explained by a high covering factor of lower ionization gas in the NLR. We also investigate effective methods for teaching astronomy and connections between astronomical topics in student learning and understanding. After developing the curriculum for a hands-on, learner-centered astronomy course (Hands-on-Science, hereafter HoS) aimed at pre-service elementary teachers, we measure student performance in HoS compared to traditional, large lecture courses (hereafter Astro101). We utilize distractor-driven multiple choice assessments in order to quantitatively assess student understanding and evaluate the persistence or correction of common misconceptions in astronomy. We find that for the topics included in the HoS curriculum, HoS students have a higher average post-test score, and higher normalized gains, than the Astro101 students. We cannot pinpoint the exact cause of this student achievement because of the multitude of nontraditional practices incorporated into the HoS implementation. Increased time-on-task, a classroom environment structured around student discussion, or focus on conceptual understanding could each be key factors in the high achievement of HoS students. We conclude that the HoS students are better prepared in astronomy for their future careers as elementary school teachers by HoS courses than they would have been in traditional, introductory astronomy courses. When we compare directly between topics covered in both HoS and Astro101, we find that HoS students have normalized gains that are a factor of 2-4 higher than those of Astro101 students. Therefore, we conclude that curricula similar to the HoS approach would benefit Astro101 students as well, particularly for topics which are most impacted by the HoS method, such as Moon phases and seasons. Lastly, a PCA of the changes in HoS student scores reveals that there is very little systematic student variation apart from the trends apparent in the mean changes in the sample. Thus, we do not find groupings of questions that some subsets of students systematically learn more readily than others. Another way to interpret this result is that the HoS curriculum and methodology indiscriminately help all kinds of pre-service elementary teachers, despite presumptive differences in their own learning styles and strengths. / text

It is now well established that stellar winds of hot stars are fragmentary and that the X-ray emission from stellar winds has a strong contribution from shocks in winds. Chandra high spectral resolution observations of line profiles of O and B stars have shown numerous properties that had not been expected. Here we suggest explanations by considering the X-rays as arising from bow shocks that occur where the stellar wind impacts on spherical clumps in the winds. We use an accurate and stable numerical hydrodynamic code to obtain steady state physical conditions for the temperature and density structure in a bow shock. We use these solutions plus analytic approximations to interpret some major X-ray features: the simple power-law distribution of the observed emission measure derived from many hot star X-ray spectra and the wide range of ionization stages that appear to be present in X-ray sources throughout the winds. Also associated with the adiabatic cooling of the gas around a clump is a significant transverse velocity for the hot plasma flow around the clumps, and this can help to understand anomalies associated with observed line widths, and the differences in widths seen in stars with high and low mass-loss rates. The differences between bow shocks and the planar shocks that are often used for hot stars are discussed. We introduce an ‘‘on the shock’’ approximation that is useful for interpreting the X-rays and the consequences of clumps in hot star winds and elsewhere in astronomy.

No description available.

"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 ~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 ((n_e), the distance of outflows to the central quasar (𝑅), and the kinetic energy carried by the outflow (𝐸̇_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 [𝑂_III λ5007 emission profile decreases with increasing n_e 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 ~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 (n_e), the distance of outflows to the central quasar (𝑅), and the kinetic energy carried by the outflow (𝐸̇_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 [𝑂_III] λ5007 emission profile decreases with increasing n_e 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.

Quasars can affect their surrounding environment through a process known as active galactic nucleus (AGN) feedback, through which the quasar can curtail the formation of stars, regulate the evolution of its host galaxy, and affect its surrounding environment in other ways. One possible mechanism for this process is a quasar's outflow, which can be observed as blueshifted absorption troughs in the quasar's spectrum. With enough kinetic power, an outflow can contribute to AGN feedback, regulating star formation and host galaxy evolution. By analyzing spectra from the Very Large Telescope (VLT) Ultraviolet Echelle Spectrograph (UVES) and the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), we determined the physical parameters of the absorption outflows of five different quasars: including electron number density, Hydrogen column density, ionization parameter, distance from the source, and kinetic luminosity. We have found that an outflow's chemical abundance can be a determining factor of its ability to contribute to feedback effects. Particularly notable outflows include a mini broad absorption line (BAL) outflow system of SDSS J0242+0049, which we estimated to be ∼ 67 kpc away from the quasar, which is the farthest distance a mini-BAL has been found from its source. We also found a high velocity C IV BAL from the same quasar which showed noticeable signs of time variability, which suggests that the ionization of the outflow has changed over time. Another was SDSS J1321-0041 which displayed BAL troughs of C II and Si II, an unusual feature for an outflow of its type. In our analysis of the EUV500 BAL of QSO B0254-3327B, we compared it with other EUV500 outflows that have been previously studied, with a total sample of 24 outflows. In that comparison, we have found that the outflow of QSO B0254-3327B was one of the most ionized outflows in the sample. We have also found a weak negative correlation between logR and log |v|, where R is the distance of the outflow from its source, and v is the velocity of the outflow, with a Spearman rank of -0.43 and p value of 0.05, suggesting that the farther the outflow is from its source, the slower its velocity. / Doctor of Philosophy / From the prediction of their existence by general relativity, to the first direct image from the Event Horizon Telescope, black holes have been a fascinating subject for both physicists and the public alike. Most massive galaxies, including our own, are said to have a supermassive black hole (SMBH) at their center. In some galaxies, an accretion disk of orbiting matter forms around the black hole, in which gravitational energy is converted into light. This can sometimes cause the galactic nucleus to shine as bright as a star in the night sky, despite it being tens of thousands of times farther away from us than any star in our own galaxy. Such galactic nuclei are called "quasars", or "quasi-stellar objects". Some quasars show signs of outflowing gases which can absorb some of their emitted light. These are observed as blueshifted absorption troughs in quasar spectra from telescopes such as the Very Large Telescope (VLT) or the Hubble Space Telescope (HST). It is predicted that, with enough power, these outflows can contribute to a process called active galactic nucleus (AGN) feedback, through which the quasar can curtail the formation of stars, regulate the evolution of its host galaxy, and affect its surrounding environment in other ways. This dissertation discusses the study of five different quasars and their outflows observed with VLT and HST. We determined the physical parameters of the outflows such as electron number density, Hydrogen column density, ionization parameter, and distance of the outflow from its source, to ultimately find each outflow's kinetic luminosity, or kinetic power. While we found that some outflows are likely to be able to contribute to AGN feedback, there are a number of unknowns that still remain. Some interesting outflows we have found include the mini-BAL outflow of SDSS J0242+0049, which we found to be at a distance of ∼ 67 kpc (or ∼ 220, 000 lightyears) away from its source, the farthest distance observed to date. We also analyzed the extreme UV outflow of QSO B0254-3327B, which we compared to other outflows observed in a similar wavelength range. In that comparison, we found a weak negative correlation between velocity and outflow distance from the central source, suggesting that the farther away an outflow is from the quasar, the slower it becomes.