Astrophysics and Astronomy Commons^™

Almost Dark Galaxies: The Search For Optical Counterparts, Quinton O. Singer

Macalester Journal of Physics and Astronomy

Presented in this paper are results from neutral hydrogen (HI) imaging and analysis of the "Almost Dark" galaxies AGC 219533, AGC 227982, and AGC 268363 using new, higher resolution observations from the Very Large Array (VLA). Selected from the ALFALFA survey, "Almost Dark" galaxies possess significant HI reservoirs but, when the HI data is compared to survey-depth ground-based optical imaging, their optical stellar counterparts have extremely low surface brightnesses. AGC 219533 is one such object. The other two sources, AGC 227982 and AGC 26833, were candidate dark galaxies, as no stellar counterpart was identified in initial ALFALFA optical matching, and …

Intervalley Scattering Rates In Tellurium Observed Via Time-Resolved Terahertz Spectroscopy, Joshua R. Rollag

Macalester Journal of Physics and Astronomy

We conducted time-resolved terahertz spectroscopy measurements on the elemental semiconductor tellurium. Pump-probe measurements were used to find the conductivity as a function of time in single crystalline tellurium samples. It was found that the excitation dynamics in tellurium changes for photon energies of 1.03 eV and 1.55 eV. The change in these excitation dynamics was attributed to intervalley scattering effects. A model using intervalley scattering and Auger recombination was fit to the data, giving a value of 2.28 ps for the intervalley scattering time constant in tellurium.

Transient Photoconductivity Of A Thermoelectric Nanomaterial Pedot:Pss With Tecu Nanowires, Gunnar J. Footh, Michaela S. Koller, James Heyman

Macalester Journal of Physics and Astronomy

Thermoelectric materials are able to transfer heat energy into electrical energy. They have many important applications, and an increased understanding of them would allow the scientific community to develop more efficient thermoelectrics. We provide here transient photoconductivity measurements of a thermoelectric nanomaterial - PEDOT:PSS with TeCu nanowires on quartz substrate. Increased copper concentration in nanowires decreases photoconductivity in both transmission and reflectance measurements. Fermi blocking provides a reasonable explanation for this decrease in photoconductivity, which occurs when total nanowire mass approaches ~15% copper concentration.

A Direct Comparison Of Lyman-Alpha And Neutral Hydrogen Morphologies, Kathleen Fitzgibbon, John M. Cannon

Macalester Journal of Physics and Astronomy

The Lyman-Alpha Reference Sample (LARS) and its extension (eLARS) represent an exhaustive campaign to reverse-engineer galaxies. The main goal is to understand how \lya radiation is transported within galaxies: what fraction of it escapes, and what physical properties affect the \lya morphology and radiative transport (e.g., dust and gas content, metallicity, kinematics, properties of the producing and underlying stellar populations). Two galaxies from the sample, LARS02 and LARS09, were observed using the B and C configurations of the Very Large Array to examine the neutral hydrogen emission, which can be used to determine a galaxy's neutral hydrogen (HI) structure and …

Contributing To Astropy: A Community Python Library For Astronomers, Asra Nizami

Macalester Journal of Physics and Astronomy

This paper discusses the author’s contributions to two packages affiliated with Astropy, a community Python library for astronomers. The packages the author contributed to were modeling, a sub-package within the core Astropy package, and WCSAxes, an Astropy affiliated package, outside the core package.

Energetic Behavior Of Resistive Random-Access Memory Cells, Christopher M. Bisbee

Macalester Journal of Physics and Astronomy

In order to investigate the switching characteristics of Resistive Random Access Memory cells (ReRAM) in terms of their thermodynamic free energy properties, we need to build a number of models that replicate the system. This report contains the models used to investigate filament growth patterns based on different boundary conditions applied to the electrode-filament system. Using Comsol Multiphysics software, we determined that when a fixed voltage is applied to each electrode in the electrode-filament system, we should expect filament dissolution that resets our cells into the High Resistance State (HRS). If we instead fix a set amount of charge on …

Simulating Correlated Disorder In Spin Glass, Jared D. Willard

Macalester Journal of Physics and Astronomy

Almost all materials undergo spontaneous symmetry breaking at sufficiently low

temperatures. For most magnetic materials, the spin rotational symmetry is broken

to form magnetic ordering. The discovery of metallic alloys which fail to form

conventional magnetic order has remained a puzzle for the last few decades.

Unfortunately, analytical calculations cannot provide an unbiased answer for the

problem. Furthermore, on the numerical side, Monte Carlo simulations require

extremely long equilibration times. The parallel tempering method has proven a

powerful tool to alleviate the long equilibration time. With the extensive efforts of

numerical simulation research, some of the idealized models have been …

Ultrafast Photoconductivity Measurements Of A Thermoelectric Nanocomposite: Tellurium Nanowire/Pedot:Pss, Brittany A. Ehmann

Macalester Journal of Physics and Astronomy

This project explores the conductivity properties of a novel thermoelectric hybrid material (Tellurium nanowires in a conducting polymer PEDOT:PSS) using both static and time-resolved conductivity measurements. We find that the effect of the conducting polymer PEDOT is weak and that the observed differences in conductivity measurements between the hybrid and non-hybrid material are most likely caused by the different sizes of the nanowires.

Mid-Ir Excitation Of Graphene, Andrew R. Banman, James Heyman

Macalester Journal of Physics and Astronomy

In this research we investigate how the conductivity of graphene changes in response to mid-infrared photoexcitation. Our p-type sample was formed through chemical vapor deposition. Pump/probe methodology produced the time-resolved Terahertz transmission, from which the photoconductivity was calculated. We probed the sample with energies above and below the Fermi energy, which was determined by Fourier transform infrared spectroscopy. Our results support a model in which heating of the electron gas, leading to high carrier scattering rates, is responsible for a decrease in conductivity. We observe this negative photoconductivity at all pump energies, allowing us to rule out the possibility of …

The Role Of Cold Gas In Low-Level Supermassive Black Hole Activity, Erik D. Alfvin

Macalester Journal of Physics and Astronomy

The nature of the relationship between low-level supermassive black hole activity and galactic cold gas, if any, is currently unclear. It has been hypothesized that feedback may heat or expel gas and quench star formation; alternatively, central black holes may feed at higher rates (either directly or as a secondary effect from stellar winds) in gas-rich galaxies. We use a combination of radio data from the on-going ALFALFA survey and from the literature, along with archival X-ray flux measurements from the Chandra X-ray observatory, to investigate this potential relationship. We construct a sample of 136 late-type galaxies, with MB < −18 out to 50 Mpc, that have both HI masses and sensitive X-ray coverage. Of these, 76 host a nuclear X-ray source, a 56% detection fraction. There is a highly significant correlation between LX and Mstar with a slope of 1.5±0.2, and a tentative correlation (significant at the 2.5σ level) between LX and MHI. However, a joint fit to LX as a function of both Mstar and MHI finds no significant dependence on MHI, and similarly the residuals of LX − LX(Mstar) show no trend with MHI. We conclude that the galaxy-wide cold gas content in these spirals does not strongly influence their low-level supermassive black hole activity.

Veritas Very High Energy Observations Of The Distant Blazar 1es 0647+250, Margaret R. Molter, Jon Dumm, Lucy Fortson

Macalester Journal of Physics and Astronomy

We perform an analysis of the long- and short-term variability of the very high energy (VHE; above 100 GeV) gamma-ray emission from the newly-detected distant blazar 1ES 0647+250. Both new and archival data from the VERITAS telescope were examined, and no strong evidence for integral flux variability on any timescale was found. This lack of variability is consistent with the application of current ultra-high energy cosmic ray (UHECR) models, which can produce secondary gamma-ray emission along the line of sight from the blazar; it also allows averaging over multiyear timescales without bias, aiding in the construction of spectral energy distribution …

Finesse Measurement In Fabry-Perot Interferometers, Michael C. Darrow

Macalester Journal of Physics and Astronomy

STAR (Space-time Asymmetry Research) is an experimental satellite that will measure anisotropy in the speed of light to unprecedented resolutions using two orthogonal Fabry- Perot interferometers. In order to achieve the desired level of precision, the optical cavities must have finesse values greater than 100,000. Using two test interferometers, I tested and optimized two different experimental methods for measurement of finesse: full-width half max measurement and cavity ring-down spectroscopy. Although each technique proved valid in its own right, my work suggests that cavity ring-down spectroscopy may be more applicable for the needs of STAR.

Deposition And Analysis Of Copper Indium Disulfide For Photovoltaic Applications, Frederick Wade

Macalester Journal of Physics and Astronomy

Thin Film semiconductors were created through the methods of electrochemistry to produce a copper, indium and sulfur metal alloy that could be placed on a stainless steel substrate. We observed other properties regarding the relative indium to copper relationships and both the macro and micro structure of the final product. X-­‐ray diffraction, SEM imaging, and atomic absorption spectroscopy data suggest a relatively intact metal alloy, but also an inaccurate ratio of indium to copper.

Photometric And Spectroscopic Analysis Of Young, Nearby Open Cluster Collinder 70, Clara M. Thomann

Macalester Journal of Physics and Astronomy

We present the results of a wide-field (80’ x 80’) photometric and spectroscopic survey of the young open cluster Collinder 70, which is also known as the ORI OB 1b association, centered on the central star of Orion’s belt, ε Ori (Alnilam). Seventy Coll 70 spectroscopy targets were selected from BVRIc color magnitude diagrams for observation using the CTIO HYDRA multi-object spectrograph; we aimed to identify targets exhibiting H" in emission and a strong lithium 6708Å line in absorption. About a third of our targets (23/70 stars) are consistent with being youthful members of Coll 70. Intermediate resolution (R!20000) HYDRA …

Monte Carlo Simulation For Silicon On Silane Hwcvd For Thin Film Solar Cells, Annaleigh Smith

Macalester Journal of Physics and Astronomy

Thin film solar cells offer a viable alternative to crystal silicon solar cells. They are expected to be cheaper to fabricate because they use material more efficiently, and are deposited in a process which can create larger area solar cells [1]. However, a high deposition rate is necessary for economic viability. A Monte Carlo simulation can model the molecular interactions in hot wire chemical vapor deposition and track the position and velocity distribution of molecular species in the gas [2]. Determining the flux on the substrate can help us to increase deposition rate by adjusting control parameters accordingly [3]. As …

Galaxy Merger Identification In The Goods-South Field, Erin O'Leary

Macalester Journal of Physics and Astronomy

We analyzed a catalog of 7,628 galaxies at 0 < z < 4 from CANDELS¹ in the GOODS-South² field in order to identify a sample of galaxy mergers and interactions. Galaxy mergers are believed to play a fundamental role in galaxy evolution. Developing methods to robustly and efficiently identify mergers becomes vital with our increasing ability to study mergers at higher redshifts and in larger samples. We explored merger identification based on visual morphology classification and preliminary attempts with automated quantitative methods. Using multiple detailed visual morphology classifications for each galaxy conducted by the CANDELS structure and morphology team, we created selection criteria to …

Shield: Star Formation From Wiyn And Galex Imaging, Samilee J. Moody

Macalester Journal of Physics and Astronomy

Using images from the GALEX (Galaxy Evolution Explorer) GR6 pipeline (released 2010), as well as the WIYN 3.5m Observatory, we present a survey of the twelve SHIELD galaxies in the far-ultraviolet (FUV, 1500 Å) and near-ultraviolet (NUV, 2200 Å) filters. FUV data were available for eleven of the galaxies, AGC 749237 being the exception. Aperture photometry was performed on each image to determine the AB magnitude in the FUV and NUV filters.These values were then used to calculate flux, luminosity, and star formation rates (SFRs). Similarly, Hα images of each galaxy from WIYN (omitting AGC 749241) were analyzed to determine …

Numerical Modeling Of The Finite Well With Implications For Observing Quantum Interference Between Coherent Electron Wave, Jacob M. Moen

Macalester Journal of Physics and Astronomy

We use numerical modeling in Fortran to investigate the claims of Wollenhaupt et al. (2006) and Hommelhoff et al. (2002) regarding ultra-­short electron pulses ionized via laser excitation of a tungsten nanotip. We assume that the nanotip acts as a finite one‐dimensional potential well with the depth equal to the work function of tungsten and the width of the order of the radius of curvature of the nanotip. The interactions of propagating Gaussian wave packets are modeled in order to give insight into the temporal and spatial evolution of the generated electron wave packets. Furthermore we hope to demonstrate the …

Synthesis And Characterization Of Zinc-­‐Oxide/Polystyrene Nanocomposite Thin Films, Christopher Krapu

Macalester Journal of Physics and Astronomy

Ultra-thin films containing zinc oxide and polystyrene were prepared by sol-gel mixing and spincoating onto silicon substrate. Photoluminescent measurements were recorded following irradiation at 325 nm. We observed passivation of shallow defect states around 3.1 eV bandgap via confinement. Time-resolved photoluminescence plots suggest a significant time dependence of emission intensity related to photodegradation of the polymer matrix.

Growth Kinetics Of Zno By Magnetron Sputtering For Solar Cell Application, Nadia Foo Kune

Macalester Journal of Physics and Astronomy

The goal of this work is study the mechanism of ZnO thin film deposition by rf magnetron sputtering with an argon plasma. This research will help understand the growth kinetics of the ZnO layer in relation to the growth conditions for solar cell application. We study the rate of growth, the electrical properties, the optical transmission and the zinc to oxygen ratio of each sample as a function of growth temperature. We conclude that Zn evaporation competes with incorporation into the film by combining with an arriving O atom.

Tip-Of-The-Red-Giant-Branch Detection: Estimating The Distance To Resolved Galaxies In Shield, Ian Cave

Macalester Journal of Physics and Astronomy

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) is an ongoing study of twelve galaxies with HI masses between 10⁶ and 10⁷ Solar masses, detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. One of the important characteristics of a galaxy is its distance, since knowing that value allows us to calibrate many other factors and learn more about the galaxy. This research was focused on creating a program to systematically solve for the distance to the galaxies in SHIELD. To perform this calculation, Tip-of-the-Red-Giant-Branch (TRGB) detection was chosen, which is a popular method for galaxies with …

Electrical Conductivity Of Tellurium Nanowires On Pedot:Pss, Banteaymolu Alebachew

Macalester Journal of Physics and Astronomy

The purpose of this project is to understand the electrical conductivity and infrared absorption spectrum of a hybrid material between Tellurium nanowires and a carbon polymer called PEDOT:PSS. This hybrid material shows much higher conductivity than its components and this behavior gives a great promise for thermoelectric effect. The most intriguing property of this material is observed when taking absorption spectrum from far to near infrared. The hybrid material shows a much bigger absorption edge than Te NW. This project attempts to explain this shift using the confinement energy model and Fermi blocking (due to doping). The result from these …

Sub-Sonic Open-Return Wind-Tunnel And Measurement Apparatus, Michael Adams

Macalester Journal of Physics and Astronomy

Wind tunnels are an effective tool for understanding relationships between predicted and actual behavior of air foils in laminar flow. In order to improve the ability of Macalester College staff and students to observe and experiment with the effects of laminar air flow on various objects and systems, it was necessary to construct and test a sub-sonic open return wind tunnel. The purpose of the tests was to discover whether or not the air flow through the test section of the tunnel was laminar around the object being tested and also to evaluate the quality of an apparatus constructed to …