Far-ultraviolet Imaging Rocket Experiment (FIRE) and the imaging of star-forming regions in galaxies

I designed, built, tested and launched a sounding rocket payload to study the far-ultraviolet radiation of M51 (the Whirlpool Galaxy). This instrument, the Far-ultraviolet Imaging Rocket Experiment (FIRE, all acronyms are listed in Appendix B), produced the first ever astronomical image of 900-1000 Å light. It was designed to look at star forming regions in nearby galaxies by imaging the youngest, hottest O-type stars. Quantifying and locating the star forming regions within galaxies will directly aid galactic formation models. In addition, with the combination of the GALEX two-color images, FIRE was designed to investigate the intervening dust that significantly obscures these wavelengths. Since the accurate correction for dust is vital to measurements across the ultraviolet regime, improving dust extinction models aids a wide variety of both galactic and extra-galactic observations. Finally, FIRE demonstrated the successful use of two novel technologies, a silicon carbide imaging mirror and a pure indium filter. In addition to FIRE, I also examined the absorption of neutral hydrogen in the intergalactic medium (IGM) along quasi-stellar objects (QSO) sightlines. The IGM is expected to contain a significant fraction of baryons at all epochs, but is difficult to detect and map since it is diffuse and emits radiation weakly. An ongoing IGM debate is whether clouds of gas detected through their Lyα absorption to QSOs are truly intergalactic or are extended halos of galaxies. A definitive answer would constrain estimates of baryonic density in the local universe and enhance our understanding of the formation of its structure. The CfA Great Wall of galaxies at redshifts of 0:015 \u3c z \u3c 0:03 offers an excellent locale to probe this question. This region is over-dense in galaxies and is surrounded by under-dense galactic voids, enabling us to compare absorbers\u27 nearest galactic neighbors in highly contrasting density regions. I found 167 Lyα absorbers along eleven QSO sightlines and used a galaxy database to examine the Lyα absorber-galaxy relationship. I compare these results to previous publications and determine that Lyα absorbers and galaxies cannot trace the same large-scale structures at the megaparsec scale

Why Do Only Some Galaxy Clusters Have Cool Cores?

Flux-limited X-ray samples indicate that about half of rich galaxy clusters have cool cores. Why do only some clusters have cool cores while others do not? In this paper, cosmological N-body + Eulerian hydrodynamic simulations, including radiative cooling and heating, are used to address this question as we examine the formation and evolution of cool core (CC) and non-cool core (NCC) clusters. These adaptive mesh refinement simulations produce both CC and NCC clusters in the same volume. They have a peak resolution of 15.6 h^{-1} kpc within a (256 h^{-1} Mpc)^3 box. Our simulations suggest that there are important evolutionary differences between CC clusters and their NCC counterparts. Many of the numerical CC clusters accreted mass more slowly over time and grew enhanced cool cores via hierarchical mergers; when late major mergers occurred, the CC's survived the collisions. By contrast, NCC clusters experienced major mergers early in their evolution that destroyed embryonic cool cores and produced conditions that prevented CC re-formation. As a result, our simulations predict observationally testable distinctions in the properties of CC and NCC beyond the core regions in clusters. In particular, we find differences between CC versus NCC clusters in the shapes of X-ray surface brightness profiles, between the temperatures and hardness ratios beyond the cores, between the distribution of masses, and between their supercluster environs. It also appears that CC clusters are no closer to hydrostatic equilibrium than NCC clusters, an issue important for precision cosmology measurements.Comment: 17 emulateapj pages, 17 figures, replaced with version accepted to Ap

Vibrational spectroscopy for the triage of traumatic brain injury computed tomography priority and hospital admissions

Computed tomography (CT) brain imaging is routinely used to support clinical decision-making in patients with traumatic brain injury (TBI). Only 7% of scans, however, demonstrate evidence of TBI. The other 93% of scans contribute a significant cost to the healthcare system and a radiation risk to patients. There may be better strategies to identify which patients, particularly those with mild TBI, are at risk of deterioration and require hospital admission. We introduce a blood serum liquid biopsy that utilizes attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy with machine learning algorithms as a decision-making tool to identify which patients with mild TBI will most likely present with a positive CT scan. Serum samples were obtained from patients (n = 298) patients who had acquired a TBI and were enrolled in CENTER-TBI and from asymptomatic control patients (n = 87). Injury patients (all severities) were stratified against non-injury controls. The cohort with mild TBI was further examined by stratifying those who had at least one CT abnormality against those who had no CT abnormalities. The test performed exceptionally well in classifications of patients with mild injury versus non-injury controls (sensitivity = 96.4% and specificity = 98.0%) and also provided a sensitivity of 80.2% when stratifying mild patients with at least one CT abnormality against those without. The results provided illustrate the test ability to identify four of every five CT abnormalities and show great promise to be introduced as a triage tool for CT priority in patients with mild TBI

First results from a next-generation off-plane X-ray diffraction grating

Future NASA X-ray spectroscopy missions will require high throughput, high resolution grating spectrometers. Off-plane reflection gratings are capable of meeting the performance requirements needed to realize the scientific goals of these missions. We have identified a novel grating fabrication method that utilizes common lithographic and microfabrication techniques to produce the high fidelity groove profile necessary to achieve this performance. Application of this process has produced an initial pre-master that exhibits a radial (variable line spacing along the groove dimension), high density (>6000 grooves/mm), laminar profile. This pre-master has been tested for diffraction efficiency at the BESSY II synchrotron light facility and diffracts up to 55% of incident light into usable spectral orders. Furthermore, tests of spectral resolving power show that these gratings are capable of obtaining resolutions well above 1300 (λ/Δλ) with limitations due to the test apparatus, not the gratings. Obtaining these results has provided confidence that this fabrication process is capable of producing off-plane reflection gratings for the next generation of X-ray observatories