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Thumbnail of Unraveling NGC 3169
Spiral galaxy NGC 3169 looks to be unraveling like a ball of cosmic yarn. It lies some 70 million light-years away, south of bright star Regulus toward the faint constellation Sextans. Wound up spiral arms are pulled out into sweeping tidal tails as NGC 3169 (left) and neighboring NGC 3166 interact gravitationally. Eventually the galaxies will merge into one, a common fate even for bright galaxies in the local universe. Drawn out stellar arcs and plumes are clear indications of the ongoing gravitational interactions across the deep and colorful galaxy group photo. The telescopic frame spans about 20 arc minutes or about 400,000 light-years at the group's estimated distance, and includes smaller, bluish NGC 3165 to the right. NGC 3169 is also known to shine across the spectrum from radio to X-rays, harboring an active galactic nucleus that is the site of a supermassive black hole.
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Professor Scott and Lisa Sommerfeldt in Missouri Independence Mission
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Alumni Adam Fennimore shares career insights for current students
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BYU's SPS is selected for Marsh Award for their outreach plan with Boys & Girls Club

Selected Publications

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By Christian D. Draper, J. Ward Moody, Stephen R. McNeil, Michael D. Joner, Rochelle Steele, and Jackson Steele
Abstract:

The population density of dwarf galaxies in low-density voids is likely determined by the dark matter halo mass function and how galaxy formation proceeds in smaller halos. This depends on the nature of dark matter itself, making the dwarf galaxy population a tracer of its properties. While dwarfs have been found in smaller, closer voids, they have proven difficult to find in larger, more distant voids through magnitude-limited spectroscopic surveys. This is because these surveys detect an overwhelmingly large number of objects behind the voids that must be verified spectroscopically, making void surveys prohibitively inefficient and expensive in terms of large-telescope time. Narrowband imaging for emission lines such as Hα reduces the number of background objects, although the overall number remains large. If imaging is done through a filter set with overlapping transmission wings, then object redshift can be estimated from photometry alone. The precision possible is an order of magnitude greater than single-band photometry, with the caveat that the captured line must be identified through other means. Broadband photometry can be used to reject enough objects with emission of an unwanted type to make obtaining spectra of the remaining objects feasible. In this study, we present an Hα survey for dwarf galaxies with Mr' fainter than −14 mag through the center 4.3 square degrees of the void FN8. Using Sloan $g^{\prime} ,r^{\prime} ,i^{\prime} $ photometry, we exclude enough [O ii] and [O iii] emitters that follow-up spectra of only a few dozen objects are required to statistically estimate the void population density.

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By Matthew A. Christian, Kent L. Gee, Jacob B. Streeter, and Alan T. Wall (et al.)
Abstract:

In a recent study of noise from a T-7A-installed GE F404 engine, microphones along a 76 m (250 ft) arc were mounted 1.8 m (5 ft) above the ground to quantify human impacts. While helpful for this purpose, the resulting multipath effects pose challenges for other acoustical analyses. For jet noise runup measurements, these effects are complicated by the fact that the noise source is extended and partially correlated, and its spatial properties are frequency dependent. Furthermore, a finite-impedance ground surface and atmospheric turbulence affect interference nulls. This study applies a ground-reflection method developed previously [Gee et al., Proc. Mtgs. Acoust. 22, 040001 (2014)] for rocket noise measurements. The model accounts for finite ground impedance, atmospheric turbulence, and extended source models that are treated as coherent and incoherent arrays of monopoles. Application to the ground runup data to correct the 76 m spectra at a range of angles suggests the incoherent line source model is more appropriate at upstream and sideline angles whereas the coherent source model is more appropriate for downstream propagation. Comparisons with near-field data and similarity spectra show that, while imperfect, this method represents an advancement in correcting jet noise spectra for ground reflection effects.

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By Samuel D. Bellows and Timothy W. Leishman
Abstract:

Acousticians typically consider the acoustic center of a source to be the point from which sound waves appear to diverge spherically. Many applications require the center's accurate determination, but its deeper significance and means of assessment have often remained ambiguous. This work revisits the acoustic center and shows how a low-frequency sound radiator with omnidirectional far-field directivity has a center defined by its dipole-to-monopole moment ratio. This definition yields conclusive results for several theoretical sources and highlights the limitations of characterizing the acoustic center only in terms of an equivalent point source.

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By Benjamin Francis and Mark K. Transtrum (et al.)
Abstract:

Superconducting radio-frequency (SRF) resonators are critical components for particle accelerator applications, such as free-electron lasers, and for emerging technologies in quantum computing. Developing advanced materials and their deposition processes to produce RF superconductors that yield n & omega; surface resistances is a key metric for the wider adoption of SRF technology. Here, ZrNb(CO) RF superconducting films with high critical temperatures (T-c) achieved for the first time under ambient pressure are reported. The attainment of a T-c near the theoretical limit for this material without applied pressure is promising for its use in practical applications. A range of T-c, likely arising from Zr doping variation, may allow a tunable superconducting coherence length that lowers the sensitivity to material defects when an ultra-low surface resistance is required. The ZrNb(CO) films are synthesized using a low-temperature (100 - 200 & DEG;C) electrochemical recipe combined with thermal annealing. The phase transformation as a function of annealing temperature and time is optimized by the evaporated Zr-Nb diffusion couples. Through phase control, one avoids hexagonal Zr phases that are equilibrium-stable but degrade T-c. X-ray and electron diffraction combined with photoelectron spectroscopy reveal a system containing cubic & beta;-ZrNb mixed with rocksalt NbC and low-dielectric-loss ZrO2. Proof-of-concept RF performance of ZrNb(CO) on an SRF sample test system is demonstrated. BCS resistance trends lower than reference Nb, while quench fields occur at approximately 35 mT. The results demonstrate the potential of ZrNb(CO) thin films for particle accelerators and other SRF applications.

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By Sharisse Poff, Daniel Tebbs, Robert C. Davis, and Shiuh–hua Wood Chiang
Abstract:

The ability to monitor a varying impedance has a range of applications, including the measurement of biological properties using bioimpedance analysis. For this type of impedance monitoring, the human heartbeat plays a role, motivating a desire to monitor pulsatile impedance changes. A four-point circuit for pulsatile impedance monitoring is designed, simulated, and built on a PCB. The circuit design is described. The circuit's ability to measure constant impedance across frequency and extract lumped element values is characterized. Using a photoresistor setup, the circuit's response to pulsatile impedance variation ranging from 500 Ω to 70 kΩ is measured and analyzed. The measured circuit settling time for an impedance change as large as 70 kΩ is 40 milliseconds, sufficient speed for heartbeat-rate pulsatile impedance monitoring.

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By G. Apolonio, A. Bugg, K. Epps, M. D. Joner, M. Spencer, and J. B. Trump (et al.)
Abstract:

We study the broadband emission of Mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, MAGIC, Fermi's Large Area Telescope (LAT), NuSTAR, Swift, GASP-WEBT, and the Owens Valley Radio Observatory. Mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. Nonetheless, significant flux variations are detected at all wave bands, with the highest occurring at X-rays and very-high-energy (VHE) γ-rays. A significant correlation (>3σ) between X-rays and VHE γ-rays is measured, supporting leptonic scenarios to explain the variable parts of the emission, also during low activity. This is further supported when we extend our data from 2008 to 2020, and identify, for the first time, significant correlations between the Swift X-Ray Telescope and Fermi-LAT. We additionally find correlations between high-energy γ-rays and radio, with the radio lagging by more than 100 days, placing the γ-ray emission zone upstream of the radio-bright regions in the jet. Furthermore, Mrk 501 showed a historically low activity in X-rays and VHE γ-rays from mid-2017 to mid-2019 with a stable VHE flux (>0.2 TeV) of 5% the emission of the Crab Nebula. The broadband spectral energy distribution (SED) of this 2 yr long low state, the potential baseline emission of Mrk 501, can be characterized with one-zone leptonic models, and with (lepto)-hadronic models fulfilling neutrino flux constraints from IceCube. We explore the time evolution of the SED toward the low state, revealing that the stable baseline emission may be ascribed to a standing shock, and the variable emission to an additional expanding or traveling shock.