2020 REU Results
UW–Madison Astrophysics REU Program Summer 2020
Morgan Adams (Florida State University)
A new deconvolution algorithm for X-ray dust echo tomography
Mentor: Sebastian Heinz
We have developed a novel 2D-constrained Lucy-Richardson deconvolution algorithm to derive precise column density maps of dust clouds in the Milky Way from X-ray dust echoes. X-ray dust tomography employs observations of dust echoes caused by bright, variable X-ray sources and the object’s light curve to constrain dust distances and physical properties. Heinz et al. 2015 developed a 1D deconvolution algorithm that was used successfully on individual observations of echoes. The goal of this project is to extend that algorithm to perform the joint deconvolution of several profiles simultaneously in order to achieve better signal-to-noise and make use of short observations which would give no meaningful data if deconvolved individually. This work was supported by the National Science Foundation’s REU program in Astrophysics through NSF award AST-1852136 and NASA/Chandra grant GO9-20124X.
Malik Bossett (Northern Arizona University)
Analyzing the Surface Brightness of Galaxies in the Perseus Cluster
Mentor: Ralf Kotulla
Galaxy clusters are rich environments, with many galaxies clumped closely together in the largest gravitationally bound objects in the universe. They also stand out from their surroundings by having a noticeably different mix of galaxy types. Earlier research has shown that lenticular galaxies in the field show a variety of intrinsic light profiles, ranging from purely exponential profiles to puffed up profiles with excess light in the galaxy outskirts to truncated profiles showing a drop in light from their outskirts. Comparable galaxies in the Virgo cluster, however, do not show this variety, despite their more active environment. In this project we study surface brightness profiles of a large number galaxies in the Perseus galaxy cluster using very deep imaging data obtained using the Subaru HyperSuprimeCam instrument to see whether the lack of diversity found in Virgo is a more general phenomena or a Virgo-specific peculiarity. Ultimately this research will help astronomers better understand the evolution of galaxies, galactic clusters, and our own galaxy, the Milky Way. This work was supported by the National Science Foundation’s REU program in Astrophysics through NSF award AST-1852136.
Hannah Woodward (University of Virginia)
Cosmic Ray Anisotropy Over Times
Mentor: Paolo Desiati & Juan Carlos Diaz-Velez
IceCube is primarily a neutrino observatory, but it detects many more cosmic rays. Even before the detector was completed, a small anisotropy in cosmic ray arrival direction was found. This just means that cosmic rays are not arriving uniformly from every region of the sky. One way to parse out possible sources of this anisotropy is to look at data in different reference frames. These include the solar and sidereal frames, which can help us distinguish between effects due to Earth’s motion around the Sun, and effects that are more distant and ambiguous. Anisotropy in solar time is expected to be a dipole due to a Compton-Getting effect, but we found a slightly better fit when we included an additional quadrupole component. This could hint at small underlying sources, like a possible effect due to atmospheric tides. Even frames that do not correspond to a physical meaning, like the anti-sidereal and extended-sidereal frames, are useful. After incorporating the last few years of IceCube data, the anisotropic patterns that we observe are consistent with earlier findings. With fewer years included, earlier work could not determine the best fit for the extended-sidereal distribution. However, using data collected between 2011 and 2019, we found that the extended-sidereal distribution is not flat with high statistical significance. This means that anisotropy in the sidereal frame is modulating over time, which also creates a spurious solar signal that can be modeled and accounted for. Both the extended-sidereal and anti-sidereal distributions that we observe in the 2011 to 2019 data could be imprints of solar and sidereal interaction over a year. This work was supported by the National Science Foundation’s REU program in Astrophysics through NSF award AST-1852136.
Emily Geist (Juniata College)
Does the Giant HII Region SMC-N66 Leak Ionizing Photons?
Mentor: Jay Gallagher
SMC-N66 is a giant HII region associated with the NGC 346 young stellar complex in the Small Magellanic Cloud. The ionized gas in N66 has a diffuse structure with few well-defined ionization edges. Using archival HST and ground-based data, we created an Halpha emission intensity map and found a non-uniform, extended distribution that shows gaps and holes within the ionized region. Our analysis suggests that there are areas where the high-energy ionizing photons could be escaping from the nebula. Current estimates for the production of ionizing photons from massive stars relative to the ionization rate in N66 indicate that Lyman continuum photons may be escaping, although a final answer depends on better knowledge of the effects of dust extinction and the stellar Lyman continuum fluxes. This work was supported by the National Science Foundation’s REU program in Astrophysics through NSF award AST-1852136.
Carlos Ortiz-Quintana (University of PuertoRico)
Forecasting the sensitivity for low-luminosity galaxies in the Local Volume with LSST + Roman + Euclid
Mentor: Keith Bechtol
Modern ΛCDM theory predicts more dwarfs in the Local Volume than what our telescopes have found. Most of these unseen dwarfs are predicted to be ultra-faint galaxies that would be detected by their individual member stars. Thus, the most reasonable explanation for the current number of observed galaxies is the limited sensitivity of existing galaxy surveys. One possible way to detect more distant ultra-faint galaxies is to combine deep optical and near-infrared imaging to produce a more complete dataset of the sky. Hence, we used python codes as well as simulated data from the Vera Rubin Observatory and Nancy Roman Space Telescope to study the star-galaxy separation techniques that are critical for the detection of more ultra-faint galaxies; specifically, we used DESC DC2 and Roman DC2 Simulations as our main catalogs. Results show that the classification accuracy for Rubin Observatory data alone is very good for bright objects, but becomes inaccurate for dimmer ones due to the abundance of faint unresolved galaxies. We identified distinct patterns in the color-color and color-magnitude distributions of stars and galaxies. We further demonstrated a method for star-galaxy separation based on the distance from the color-color stellar locus distribution in addition to a morphological classifier, providing an adjustable classifier to have a more complete or more pure stellar sample in the Rubin data. This research demonstrated that it is possible to increase the stellar efficiency using alternative methods in addition to extendedness. Further research is needed to optimize star-galaxy classification with the combination of ground-based optical and space-based near-IR imaging.
Lily Robinthal (Evergreen State College)
Mapping the Invisible: 21-cm intensity mapping with the Tianlai Array
Mentor: Peter Timbie
21-cm intensity mapping is a new method of mapping the universe using the 21-cm spectral line of neutral hydrogen. Because hydrogen is so prevalent in the universe, this method allows astronomers to image large swaths of the universe and periods from before stars were formed in the radio region of the electromagnetic spectrum, as well as compare to optical surveys. This can ultimately be used to investigate the large-scale structure of the universe, and to study dark energy. I am modeling optical data from a spectroscopic galaxy redshift survey of the North Celestial Cap. This data will be compared to 21-cm data of the same region from the Tianlai Array, a new 21-cm survey. I am also working with data from the Arecibo Legacy Fast ALFA (ALFALFA) survey, a different 21-cm survey, which can be correlated with optical data from the Sloan Digital Sky Survey. This will give us a sense of how the optical survey of the NCC will compare to the Tianlai survey. This work was supported by the National Science Foundation’s REU program in Astrophysics through NSF award AST-1852136.
Jenniffer Profitt (Columbia University)
Protection for a New Generation of Spacecraft: Evaluating the feasibility of active shielding systems using magnetic fields
Mentor: Elena D’Onghia, Paolo Desiati
Long-term spaceflight and space-based instruments require protection from cosmic radiation, and active shielding could reduce the mass, consolidate the radiation deflection system, and provide higher efficiency than passive shielding using bulk materials. Multiple magnetic field geometries were tested and 9 proton energies (spread over a logarithmic scale) were simulated for each geometry to determine which is most efficient at protecting a small, central region of 3D space from varying levels of cosmic radiation. To determine the efficiency, proton particle trajectories for each energy from 0.1 MeV to 1 GeV were generated; the distance from each coordinate to the center was calculated for every particle in the trajectory; and from these distances, a minimum distance was determined. If this distance did not reach the target region, the shielding efficiency was incremented. The results showed that the solenoid magnetic field of 11 coils and 10 meter radius provided the weakest overall shielding; the geomagnetic dipole proved strongest for a central region of 1 meter radius and for central regions of 3 meter and 5 meter radii for low proton energies (at or below ~30 MeV); and the circular coil wire field was strongest for central regions of 3 meter and 5 meter radii for high proton energies (at or above ~100 MeV). This research is important for near-future aerospace engineering applications (especially for long-term, reusable crewed landers) as well as for providing a simulation of the behavior of cosmic rays along field lines of various magnetic field geometries.
Aliyah Postell (University of Arizona)
The NGC 1275 High Velocity System: The Verging Merge
Mentor: Jay Gallagher
In roughly 30-40 million years, the High Velocity System (HVS) of NGC 1275 will complete its collapse into the center of the Perseus cluster. As part of this infalling process, streams of dust and gas have been severed from the center of HVS. Our area of focus is the properties of these filaments. We combined new velocity measurements of one filament with data in the literature with estimates of gas masses from dark nebulae to gain insights into the properties of the HVS. The results concur with previous studies in finding that the HVS is an infalling spiral galaxy that has become a tidally-stripped “jellyfish” system. This work was supported by the National Science Foundation’s REU program in Astrophysics through NSF award AST-1852136.