We have used the Hubble STIS and FUSE archives of ultraviolet spectra of bright AGNs to identify intergalactic Lya absorbers in nearby (z ≤ 0.1) voids. From a parent sample of 651 Lyα absorbers, we identified 61 "void absorbers" located >1.4 h70-1 Mpc from the nearest L* or brighter galaxy. Searching for metal absorption in high-quality (S/N > 10) spectra at the location of three diagnostic metal lines (O VI λ1032, C IV λ1548, Si III λ1206), we detected no metal lines in any individual absorber, or in any group of absorbers using pixel co-addition techniques. The best limits on metal-line absorption in voids were set using four strong Lya absorbers with NHI > 1014 cm-2, with 3 σ equivalent-width limits ranging from 8 mÅ (O VI) to 7-15 mÅ (C IV) and 4-10 mÅ (Si III). Photoionization modeling yields metallicity limits Z < 10 -1.8±0.4 Z⊙ from nondetections of C IV and VI, some ∼6 times lower than those seen in Lyα/O VI absorbers at z < 0.1. Although the void Lyα absorbers could be pristine material, considerably deeper spectra are required to rule out a universal metallicity floor produced by bursts of early star formation, with no subsequent star formation in the voids. The most consistent conclusion derived from these low-z results and similar searches at z = 3-5 is that galaxy filaments have increased their mean IGM metallicity by factors of 30-100 since z ∼ 3.

We report the discovery of a dwarf (MB = -13.9) poststarburst galaxy coincident in recession velocity (within uncertainties) with the highest column density absorber (NHI = 1015.85 cm-2 at cz = 1586 km s-1) in the 3C 273 sight line. This galaxy is by far the closest galaxy to this absorber, projected just 71 h70-1 kpc on the sky from the sight line. The mean properties of the stellar populations in this galaxy are consistent with a massive starburst ≈3.5 Gyr ago, whose attendant supernovae, we argue, could have driven sufficient gas from this galaxy to explain the nearby absorber. Beyond its proximity on the sky and in recession velocity, the further evidence in favor of this conclusion includes both a match in the metallicities of absorber and galaxy and the fact that the absorber has an overabundance of Si/C, suggesting recent Type II supernova enrichment. Thus, this galaxy and its ejecta are in the expected intermediate stage in the fading dwarf evolutionary sequence envisioned by Babul & Rees to explain the abundance of faint blue galaxies at intermediate redshifts. While this one instance of a QSO metal-line absorber and a nearby dwarf galaxy is not proof of a trend, a similar dwarf galaxy would be too faint to be observed by galaxy surveys around more distant metal-line absorbers. Thus, we cannot exclude the possibility that dwarf galaxies are primarily responsible for weak (NHI = 1014-1017 cm-2) metal-line absorption systems in general. If a large fraction of the dwarf galaxies expected to exist at high redshift had a similar history (i.e., they had a massive starburst that removed all or most of their gas), these galaxies could account for at least several hundred high-z metal-line absorbers along the line of sight to a high-z QSO. The volume-filling factor for this gas, however, would be less than 1%.

Symbiotic stars are binaries consisting of a cool evolved G-M/S/C I-III star accreting onto a smaller companion---but the accretion disk itself is rarely detected. Accretion signatures like hard X-rays and optical/ultraviolet flickering are usually suppressed or outshone by shell burning on the accreting white dwarf, the luminous giant, and the giant's wind nebula. In Chapters 2 and 3, we present a new way to find symbiotics that is less biased against accreting-only, non-burning symbiotics with directly detectable accretion disks. Our search methodology is based on finding outliers in SkyMapper Southern Sky Survey broad-band and intermediate-band photometry, using a parameter space built from reconstructed u-g u-v snapshot colors and rapid variability between the three exposures of a 20-minute SkyMapper Main Survey filter sequence, from a sample of luminous red objects selected with 2MASS and Gaia. In a pilot survey employing this new search design, we discovered 12 new symbiotics, including four symbiotics with optical accretion disk flickering and at least two with boundary-layer hard X-rays, as well as 10 new symbiotic candidates. We also discovered optical flickering in the known symbiotic V1044 Cen (CD-36 8436). We conclude that at least 20% of the true population of symbiotics exhibits detectable optical flickering from the inner accretion disk, a substantial fraction of which would not meet the usual H-alpha equivalent width detection thresholds typically used to find symbiotics with traditional narrow-band emission line photometry surveys. There is a significant population of optically-flickering symbiotics hidden both within and beyond the known catalogs of symbiotic stars---however, the question of whether the true population of accreting-only symbiotics is larger than the population of burning symbiotics remains unanswered. We also find that our methods probe a completely different region of parameter space than recent work by the Munari et al. (2021) search for accreting-only symbiotics, while being surprisingly in harmony with the Akras et al. (2019) infrared selection criteria. As an intermediate step in our pilot survey, we explored several outlying regions in our SkyMapper parameter space with optical spectroscopy of 234 luminous red objects, which we present in a 248-page spectral atlas. Our results identify a zone of the u-g u-v snapshot color-color diagram in which virtually all objects are symbiotics. When all-sky uvg colors become available through future DRs of SkyMapper and MEPHISTO, between about 51 and 117 symbiotics missed by previous surveys (of which 11 to 17 have been reported in this work) will be discoverable using only this mostly-symbiotic zone of the color-color diagram, with a near-zero contamination rate. Main Survey filter-sequence variability is also a powerful tool for finding hidden, flickering symbiotics both inside and outside of the mostly-symbiotic color-color zone, but variability must still be used in conjunction with color; there must be enough of an accretion disk contribution to the u-band for it to exhibit detectable variability. We show that yellow post-AGB stars with strong Balmer jump absorption (along with the symbiotic Southern Crab) are outliers with large positive u-v, while some S and carbon stars are outliers with large negative u-v. We also show that it is important to correct the results of SkyMapper's catalog pipeline for variability when dealing with samples containing large-amplitude pulsating stars. In Chapters 4 and 5, we present an in-depth study of one of the few optically-flickering symbiotic stars previously known, MWC 560 (V694 Mon). The persistent outflow from MWC 560 is known to manifest as broad absorption lines (BALs), most prominently at the Balmer transitions. In Chapter 4, we report the detection of high-ionization BALs from C IV, Si IV, N V, and He II in International Ultraviolet Explorer spectra obtained on 1990 April 29-30, when an optical outburst temporarily erased the obscuring "iron curtain" of absorption troughs from Fe II and similar ions. The C IV and Si IV BALs reached maximum radial velocities at least 1000 km/s higher than contemporaneous Mg II and He II BALs; the same behaviors occur in the winds of quasars and cataclysmic variables. An iron curtain lifts to unveil high-ionization BALs during the P Cygni phase observed in some novae, suggesting by analogy a temporary switch in MWC 560 from persistent outflow to discrete mass ejection. At least three more symbiotic stars exhibit broad absorption with blue edges faster than 1500 km/s; high-ionization BALs have been reported in AS 304 (V4018 Sgr), while transient Balmer BALs have been reported in Z And and CH Cyg. These BAL-producing fast outflows can have wider opening angles than has been previously supposed. BAL symbiotics are short-timescale laboratories for their giga-scale analogs, broad absorption line quasars (BALQSOs), which display a similarly wide range of ionization states in their winds. In Chapter 5, we investigate how the accretion disc of MWC 560 is affected by its outflow. We performed optical, radio, X-ray, and ultraviolet observations of MWC 560 during its 2016 optical high state. We tracked multi-wavelength changes that signalled an abrupt increase in outflow power at the initiation of a months-long outflow fast state, just as the optical flux peaked: (1) an abrupt doubling of Balmer absorption velocities; (2) the onset of a 20 𝜇Jy/month increase in radio flux; and (3) an order-of-magnitude increase in soft X-ray flux. Juxtaposing to prior X-ray observations and their coeval optical spectra, we infer that both high-velocity and low-velocity optical outflow components must be simultaneously present to yield a large soft X-ray flux, which may originate in shocks where these fast and slow absorbers collide. Our optical and ultraviolet spectra indicate that the broad absorption-line gas was fast, stable, and dense (⪞10⁶.⁵ cm⁻³) throughout the 2016 outflow fast state, steadily feeding a lower-density (⪝10⁵.⁵ cm⁻³) region of radio-emitting gas. Persistent optical and ultraviolet flickering indicate that the accretion disc remained intact. The stability of these properties in 2016 contrasts to their instability during MWC 560's 1990 outburst, even though the disc reached a similar accretion rate. We propose that the self-regulatory effect of a steady fast outflow from the disc in 2016 prevented a catastrophic ejection of the inner disc. This behaviour in a symbiotic binary resembles disc/outflow relationships governing accretion state changes in X-ray binaries.

No description available.

No description available.

I investigate the observational signatures of the formation of dark matter cores in dwarf galaxies. I adopt the paradigm where the energy from star formation feedback is injected into the orbits of dark matter particles, forming a constant density core consistent with observations of dwarf galaxies. Using physically motivated constraints I show there is ample feedback energy available given the average stellar mass of dwarf galaxies to form cores in $10^{8}$--$10^{11}$\thinspace M$_{\odot}$ halos, and predict the maximum core size as a function of stellar mass. I describe how observational features of the old stellar content of dwarf galaxies are due to this core formation paradigm. As both dark matter and stars are collisionless fluids, the stars responsible for the feedback form in the centres of dwarf galaxies and have their orbits grown by subsequent star formation. This will naturally lead to age and metallicity gradients, with the younger and more metal rich stellar population near the dwarf centres. This process also prevents the destruction of globular clusters by driving them out of the dwarf nucleus --- the decrease in central dark matter density reduces the strength of dynamical friction --- and increases the likelihood of being stripped onto the stellar halos of larger galaxies. It also offers a model for forming multiple populations in globular clusters, with the only assumption being that the source of the polluted gas resides within the dwarf progenitor. As the orbit of a globular cluster grows, it will experience multiple accretion events with each pass through the gas-rich galaxy centre. The simple accretion model exhibits two traits revealed from observations --- a short accretion timescale and a sensitive dependence on mass --- without requiring an exotic initial stellar mass function or the initial globular cluster mass function to be 10--25 times larger than at present. / Dissertation / Doctor of Philosophy (PhD)

We use the APOSTLE suite of cosmological simulations to examine the role of the cosmic ionizing background in regulating star formation (SF) in low-mass LCDM halos. In agreement with earlier work, we find that, after reionization, SF can only proceed in halos whose mass exceeds a redshift-dependent ``critical'' virial mass determined by the structure of LCDM halos and the thermal pressure of UV-heated gas. This critical mass increases from Mcrit~10^8 Msun at z~11$ to ~10^9.7 Msun at z=0, roughly following the average mass growth history of halos in that mass range. This implies that most halos above or below critical at present have remained so since early times. In particular, the halos of most galaxies today were already above-critical (and thus forming stars) at high redshift, providing a simple explanation for the ubiquitous presence of ancient stellar populations in dwarfs, regardless of luminosity. It also implies that Mcrit today represents a ``threshold'' mass below which the fraction of ``dark'' halos increases steeply. Sub-critical halos may still host luminous galaxies if they were above-critical at some point in the past. SF ceases if a halo falls into the sub-critical regime; depending on each halo's accretion history this can occur over a wide range of times, explaining why SF in many dwarfs seems to continue well past the reionization epoch. It also suggests a tantalizing explanation for the episodic nature of SF in some dwarfs, which, in this interpretation, would be linked to temporary halo excursions above and below the critical boundary. In the simulations, Mcrit(z) cleanly separates star-forming from non-star-forming systems at all redshifts, indicating that the ionizing UV background, and not stellar feedback, is what regulates the beginning and the end of SF in the faintest dwarfs. Galaxies in sub-critical halos should make up a sizable population of faint field dwarfs, distinct from those in more massive halos because of their lack of ongoing star formation. Although few such galaxies are known at present, the discovery of this population would provide strong support for our results. / Graduate

Cardiovascular diseases (CVDs) have been recorded as the number one cause of death worldwide, accounting for 32% of total deaths annually. More than two-thirds of all CVD cases are associated with atherosclerosis, which is the accumulation of fats and other substances causing plaque formation in the interior walls of major arteries. This leads to narrowing of the lumen and hardening of the arteries, ultimately resulting in angina, heart attack and/or stroke. Studies have shown that the pathogenesis of atherosclerosis and associated CVDs is strongly linked to elevated secretion of liver-specific lipoproteins called very-low-density-lipoprotein (VLDL). VLDLs are crucial lipoproteins responsible for transportation of triacylglycerides (TAGs), chemically inert particles that are physiologically significant for their energy storing capacity, from the liver to peripheral tissues. These VLDL particles are synthesized in the lumen of the endoplasmic reticulum (ER) of hepatocytes, transported from the ER to the cis-Golgi in special transport vesicles called VLDL-transport-vesicles (VTVs) and secreted into plasma through a highly regulated secretory pathway. Previous studies from our laboratory have shown that VTV-mediated ER-to-Golgi VLDL trafficking is the rate-limiting step in overall VLDL secretion from hepatocytes into plasma. In this project, we investigated intracellular VLDL trafficking and VLDL secretion in Ames dwarf (Prop1df, df/df) mice, a mutant mouse model homozygous for a recessive mutation at Prop1 gene locus (Prop1df) having deficiency of growth hormone (GH), thyroid stimulating hormone (TSH) and prolactin (PRL). This model is characteristic of prolonged longevity (~50% longer) and improved insulin sensitivity in comparison to their wild-type (N) counterparts. Ames dwarf (df/df) mice have recently been shown to have highly reduced plasma TAG levels, associating them with reduced susceptibility to atherosclerosis and associated CVDs. The underlying mechanism responsible for reduced VLDL secretion in Ames dwarf mice is yet to be characterized. We hypothesize that VTV-mediated trafficking of VLDL is reduced in Ames dwarf mice because of reduced expression of proteins regulating VLDL and VTV formation. To test our hypothesis, we first performed VTV-budding assay using cellular fractions isolated separately from Ames dwarf (df/df) and wild-type (N) mice livers. Our results show a significant (45%) reduction in VTV-budding process in Ames dwarf (df/df) mice compared to wild-type (N). Next we performed 2-dimensional differential gel electrophoresis (2-DIGE) on VTV and whole cell lysate (WCL) samples in order to examine the differences in protein expression and to have highly specific protein separation. ExPASy database was used to analyze protein spots that allowed us in identifying proteins specifically expressed in each of the mouse groups. Employing western blotting, samples (ER, cytosol, VTV and WCL) from both sets of mice were tested for expression levels of VLDL and VTV associated proteins (ApoB100, Sec22b, CideB, MTP, Apo-A1 and Apo-AIV) with ?-actin as the loading control. Significant differences in expression level of these proteins were observed which strongly suggest that the formation of VTV from ER in male Ames dwarf (df/df) mice is reduced compared to wild-type (N). Overall, we conclude that the differential expression of proteins required for VLDL transport causes reduced VLDL secretion in male Ames dwarf (df/df) mice.

We carried out a near-infrared radial velocity search for Jupiter-mass planets around 36 late M dwarfs. This survey was the first of its kind undertaken to monitor radial velocity variability of these faint dwarfs. For this unique survey we employed the 10-m Keck II on Mauna Kea in Hawaii. With a resolution of 20,000 on the near-infrared spectrograph, NIRSPEC, we monitored these stars over four epochs in 2007. In addition to the measurement of relative radial velocity we established physical properties of these stars. The physical properties of M dwarfs we determined included the identification of neutral atomic lines, the measurement of pseudo-equivalent widths, masses, surface gravity, effective temperature, absolute radial velocities, rotational velocities and rotation periods. The identification of neutral atomic lines was carried out using the Vienna Atomic line Database. We were able to confirm these lines that were previously identified. We also found that some of the lines observed in the K-type stars, such as Mg I though weak, still persist in late M dwarfs. Using the measurement of pseudo-equivalent widths (p-EW) of 13 neutral atomic lines, we have established relations between p-EW and spectral type. Such relations serve as a tool in determining the spectral type of an unknown dwarf star by means of measuring its p-EW. We employed the mass-luminosity relation to compute the masses of M dwarfs. Our calculations indicate these dwarfs to be in the range of 0.1 to 0.07 solar masses. This suggests that some of the late M dwarfs appear to be in the Brown dwarf regime. Assuming their radii of 0.1 solar radii, we calculated their surface gravity. The mean surface gravity is, log g = 5.38. Finally their effective temperature was determined by using the spectral-type iii temperature relationship. Our calculations show effective temperatures in the range of 3000 2300 K. Comparison of these values with models in literature show a good agreement. The absolute radial and rotational velocities of our targets were also calculated. Values of rotational velocities indicate that M dwarfs are, in general, slow rotators. Using our result and that from literature, we extended our study of rotational velocities to L dwarfs. Our observations show an increase in rotational velocities from late M to L dwarfs. We also find that the mean periods of M dwarfs are less than 10 hours. In order to improve our precision in measuring relative radial velocity (RV), we employed the use of deconvolution method. With this method we were able to ameliorate relative RV precision from 300 m/s to 200 m/s. This was a substantial improvement in our ability to detect gas-giant planets. However none of the 15 dwarfs we monitored indicate a presence of companions. This null result was then used to compute the upper limit to the binary frequency and close-in Jupiter mass planetary frequency. We find the binary frequency to be 11% while the planetary frequency was 1.20%.

In this essay, I study ambivalence in Pär Lagerkvist's (1891–1974) novel The Dwarf (1944). The ambivalence is primarily expressed through Lagerkvist's use of contrasts, and enhanced by the unreliable narrator. At first glance, the contrasts might be perceived as binary oppositions, but I aim to illustrate how boundaries are dissolved, and I argue that the contrasts cannot in fact be seen as opposites. Instead, a non-binary perspective is required. Inspired primarily by Eve Kosofsky Sedgwick and Judith Butler, I use a queer reparative reading as my starting point. The analysis focuses specifically on four examples of contrasts that I claim are most prominent in the novel: love–hate, closeness–distance, superiority–inferiority, and good–evil. Although the protagonist is confused by the dissolved boundaries between these, he is the one who embodies them the most. He might seem as a hateful, inferior, and evil character who wants to maintain distance from everyone else. However, he is not inferior all the time and he also expresses more loving feelings and shows a desire to be close to others. This raises the question whether he truly is evil or if his actions are simply the result of being mistreated. Reading the novel from a non-binary perspective thus proves that we can never reach any definitive answers. Rather, we are forced to continue asking important, difficult, and sometimes uncomfortable questions.