Presentations

This is a large scale study of 1052 dark matter sub-halos in the TNG100-1 simulation from IllustrisTNG at redshift 𝑧 = 0 and within the 10^11 − 10^13.5 𝑀⊙ range. Using an asymmetry calculator and Illustris catalog data, I studied the relationship between integrated HI flux asymmetries and sub-halo mass, group halo mass, metallicity, and primordial accretion rate. There is no apparent relationship with metallicity, but there was an observed relationship between asymmetry and sub-halo mass, halo mass, and accretion rate. I also observed the progression of asymmetry over the course of the entire lifespan of four halos.

We present an analysis of the ionisation mechanisms of H𝛼 lines in a sample of Neutral Hydrogen (HI) detected galaxies with low Star Formation Rate (SFR) and compare it with that of two control samples: HI detection galaxies with High SFR and HI non-detection galaxies with Low SFR. We identify a sample of 97 galaxies for each of the sample set using integral field spectroscopy data from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) program and Wide-field Infrared Survey Explorer (WISE) Survey. Using the Baldwin–Philips–Terlevich (BPT) diagnostic diagrams, we classify the galaxies as one of Star Formation, Composite, Low-ionisation emission-line (LIER), Seyfert, Ambiguous, Other or No spaxel. We find a high fraction of LIERs in both the main sample (56%) and Low SF, HI Non-detection sample (47%) very different to the HI Detection High SFR sample (14%) . We conclude that LIERs are specific to galaxies with low SFR and not necessarily HI content. In sample of low SFR galaxies, HI detected galaxies were observed to have a greater proportion of central-LIERs (cLIER) compared to HI non-detections.

Red geysers are a specific type of quiescent galaxy, denoted by the twin jets emerging from their galactic centers. These bisymmetric jets emitted from the galaxy’s central black hole work to suppress star formation by stabilizing cool HI gas. In this paper, we explore the amount of work these winds are doing to prevent stars from developing by creating a sample of red geysers and a sample of control galaxies and stacking each to examine the average mass of HI gas in each sample. Stacking the spectra allows us to identify the mean HI content of red geysers (or to place a much stronger upper limit on the mass) even though many of the individual galaxies are HI non-detections. We find that the average red geyser has an HI gas-to-stellar mass ratio less than 0.0138 𝑀⊙, although some outlying red geysers show significantly more HI.

Astronomers are trying to discover how the neutral hydrogen in the intergalactic medium became ionized. It is thought that reionization was accomplished by galaxies in the early universe. Those galaxies are too far away for us to detect their ionizing radiation. We turn instead to galaxies much closer to us called Green Peas (GPs). GPs share a lot in common with these early universe galaxies and can help us learn how early galaxies contributed to reionization. If star clusters in these GPs are old enough to have stars that go supernova, that could be one way for ionizing or "Lyman Continuum (LyC)" radiation to escape. We looked at the ages of the star clusters in 17 different GPs using UV spectra and models to find constraints in parameters such as metallicity, age, ionization parameter, and optical depth. By finding the best fits for the models to the actual data, we can determine the ages of the star clusters in the GPs and gain insight into how LyC radiation escapes. We found that most of the GPs have star clusters old enough for supernovae and likely have one young population of stars plus a slightly older population. With our methods, we found no constraint in the ionization parameter or the optical depth for any of the galaxies, but metallicity and age were well constrained. We compared the models to optical data from the galaxies and found that the high ionization emission lines were under-predicted and the low ionization lines were over-predicted, which means ionization parameter in the best-fit was not correct. We will fit the optical and UV data simultaneously so that we can find the best-fit parameters and provide a better all-around view of these GPs and how they operate.

We examine the morphology of galaxies from the projects Galaxy Zoo 2 (GZ2), in the optical, and Galaxy Zoo: UKIDSS, in the infrared. We compare galaxy morphologies in these different filters and investigate the correlations between spiral arm winding and average central bulge size as well as the fraction of galaxies that have bars as a function of optical color. We see a lack of correlation between arm winding and central bulge size when the galaxy is viewed in both infrared and optical filters. This result is surprising as it is at odds with the Hubble Tuning Fork’s classification of galaxies. The bar fraction for galaxies in both infrared and optical appears to have similar trends, yet differs slightly from previously published work on the subject. This difference between bar fraction trends is suggested to be due to there being fewer blue and unbarred galaxies observed in both GZ2 and UKIDSS filters.

The local interstellar medium (LISM) is made of 15 separate clouds in a region of space around our Solar System that extends 15 parsecs (pc) around us. It is composed of gas and dust, and interacts with our sun’s heliosphere as it moves through space (Redfield & Linsky 2008). Astronomers have been attempting to understand what this LISM is composed of by studying sightlines within 100 pc, in order to determine its composition through its absorption features. By using the Hubble Space Telescope’s STIS observations, we studied one particular sightline 35.8 pc away (Konow et al. 2020) for its deuterium (D I) absorption. This sightline, a binary star named HD129333, had not previously been studied for ISM absorption, and its D I absorption holds implications toward our heliosphere and the ISM. Deuterium is an isotope of hydrogen, and studies of D I in the LISM are important because they can be used to help fit the important hydrogen Lyman-𝛼 line and determine the D/H ratio. This indirect method in studying hydrogen with D I is crucial to understanding the composition of the LISM and the heliosphere.

The Transiting Exoplanet Survey Satellite (TESS) mission has delivered hundreds of thou- sands of light curves from bright sources across the sky. We developed an inference framework to perform automatic anomaly detection and classification of TESS data. Our pipeline in- cludes two methods of deriving features encapsulating physical characteristics of the data. Our first dimensionality reduction method includes engineering custom features, such as statistical moments and spectral representations. Our second method employs a one-dimensional con- volutional autoencoder to learn a compressed latent space of the light curve. We use these low-dimensional representations of the TESS data to perform novelty detection as well as classification. Our method of unsupervised learning can take full advantage of TESS’ all-sky survey to produce mass classification of light curves and isolate light curves with characteristic profiles.

The escape fractions ( f𝑒𝑠𝑐 ) of potential sources of ionizing radiation in the early universe are crucial to understanding the period of reionization. The escape fractions of potential high-redshift LyC leakers cannot be directly observed. However, statistical analyses on low- redshift, star forming galaxies may help disentangle which galaxy properties can indirectly predict f𝑒𝑠𝑐 values. In my work, I run principal component regression analyses on a sample of 66 low-redshift, star-forming galaxies selected from the SDSS. Applying prediction models for f𝑒𝑠𝑐 based on features which are observable at high redshifts could reveal which sources were responsible for reionization.

Young stellar and substellar objects are often surrounded by protoplanetary disks of gas and dust. Disk mass is accreted onto its central object. The mechanisms that drive accretion should be understood over the range of masses of central objects. We study the mechanism of accretion in low-mass systems, collecting the near-infrared spectra (0.95-2.46 𝜇m) of three low-mass stars and five brown dwarfs (BDs). These observations were obtained with the Apache Point Observatory (APO) 3.5-meter telescope, which is owned and operated by the Astrophysical Research Consortium. The data was reduced with an IDL package called APOTripleSpecTool. Our aim is to find and compare accretion signatures within this range of low-mass systems and calculate their mass accretion rates. Measurements of mass accretion rates will provide a more robust understanding of how mass of the central object is related to mass accretion, as well as provide upper limits on protoplanetary disk lifetimes–which constrain whether and how exoplanets might be created–in the observed systems.

Protoplanetary disks are the dusty feeding grounds around young stars out of which planets coalesce and grow. However, their small angular sizes and dustiness present challenges for detecting and studying planets embedded within them. One means of probing the hidden properties of these disks is via spectroscopy of rovibrational emission lines of carbon monoxide (CO), whose characteristics can be an indication of an embedded planet (e.g., Brittain et al. 2014; Regály et al. 2010, 2014). We present data and analysis of a number of 12C16O 𝑣 = 1 − 0 and 𝑣 = 2 − 1 emission lines originating from the protoplanetary disks around the young stars AS 205 N and AB Aurigae with the goal of identifying variability, possibly due to planets in the disks. The data from AS 205 N clearly show emission that decreases in intensity with time. The decrease occurs primarily for molecules with lower speeds, which correspond to greater orbital distances. This phenomenon could be due either to a decrease in emitting surface area (found to be about 15%), a decrease in temperature, or some combination of the two. The emission lines from AB Aurigae showed no significant variability, but had relatively low line-to-continuum ratios.

Protoplanetary disks are flattened structures of gas and optically thick dust around young stars (<10 Myr old). Debris disks are the older, more evolved counterparts with optically thin dust levels. Recent work has shown that deviations from Keplerian rotation in the spectral line analysis of protoplanetary disks can point to the presence of exoplanets that are other- wise difficult to detect. The deviations from Keplerian rotation studied here include velocity kinks/wiggles and Doppler Flips. Doppler Flips are observable in the residuals of intensity- weighted velocity (first moment map) model fitting. The purpose of this study was to apply these methods, previously used on protoplanetary disk data, to debris disk data. We used spectral line emission data from the Atacama Large Millimeter/submillimeter Array (ALMA). We first verified the presence of velocity kinks/wiggles and Doppler Flips in the protoplanetary disk 12CO(J=2-1) emission data of HD163296 (angular resolution 0.04”, linear resolution 5 au), confirming the results of previous studies. The analysis of CI(3P1-3P0), (angular resolution 0.25”, linear resolution 14 au), and 12CO(J=3-2) emission data (angular resolution 0.13”, linear resolution 8 au), for the gas-rich debris disk 49 Ceti did not show any velocity kinks/wiggles, however disk models do indicate moderate evidence of a warp, a possibility considered in previous studies. Our analysis rules out planets orbiting 49 Ceti with semimajor axes between 60 and 260 au, and provides proof of concept for similar studies of a wider variety of debris disks in the future.

Turbulence is one of the key processes influencing planet formation, hence we are inves- tigating the mechanism driving it by studying its vertical structure. We have been working with the disk around DM Tau, since it is so far the only system where significant non-zero turbulence has been robustly detected in its upper layers using molecular line emission. To estimate turbulence near the midplane in the outer disk, we used N2H+(3-2) and DCO+(4-3) emission alongside a ray-tracing radiative transfer code with a parametric model of the disk structure and Bayesian statistics to find a best fit model. Our preliminary results show N2H+ emission inside the previously determined CO snowline. Moreover, the DCO+(4-3) emission is depleted between ∼ 104 and ∼ 156 au; which could be explained by CO freeze-out, non-thermal desorption and radial migration of dust grains.

We physically model the structure of “rubble-pile” asteroid Ryugu as a granular aggregate to set a constraint on its macroporosity. That allows us to calculate a corresponding constituent rock density to be compared to sampled meteorite densities. Models were constructed according to the power law describing Ryugu’s cumulative boulder size distribution (N=CD^alpha, where C is a constant and D is boulder diameter). With alpha values ranging from -2 to -4, the measured macroporosities range from 26% to 34%. Using a bulk density of 1.19±0.02 g/cm^3 for Ryugu, these values correspond to rock densities between 1.6 and 1.8 g/cm^3, consistent with CI meteorites, which lack chondrules. Therefore, chondrules may be less abundant in the solar system than commonly thought.

Dust-dominated debris disks are commonly found around main sequence stars, and are indicative of successful planet formation. While the mass of these disks is small compared to planets, debris dust is generally easier to detect than planets due to a larger surface area. Thus, observations of disk morphology, such as gaps and edges, can provide insight into the arrangement of planets, both seen and unseen, in the system. Millimeter wavelength observations have demonstrated that gaps are common in young protoplanetary disks, and have recently begun to be detected in older debris disks. We used an N-body code, REBOUND (Rein & Liu 2012; Rein et al. 2019), to model the interaction between putative planets and disk test particles and reproduce observational data for all debris disks with detected gaps: HD 92945, HD 15115, HD 107146, and HD 206893. Although Newton’s law of universal gravitation is easy to solve for two bodies, it can be difficult to predict the motion of three or more bodies. N-body codes integrate the equations of motion for each particle, and often make approximations to reduce complexity. There are several different proposed mechanisms in the literature for planets carving gaps in broad debris disks, including a planet embedded in the gap, an inner eccentric planet interacting with a disk of similar mass, and two inner planets in mean motion resonance. We applied each mechanism to each system in order to determine how consistently the mechanism could reproduce the observed disk structure. A planet embedded in the gap yielded results consistent with all four disks we attempted to reproduce. An inner eccentric planet with a massive disk was able to produce results comparable with HD 107146 and HD 15115. Finally, two inner planets were not able to produce a gap consistent with any of the systems.