Binary systems containing a compact object may exhibit periodic brightening episodes due to gravitational lensing of the lower-mass companion as it transits the compact object. Such self-lensing systems have been discovered before by identifying this periodic brightening in light curves. We explore the possibility of using this method to detect new compact objects with data from the Zwicky Transient Facility (ZTF). Thanks to its extensive optical variability coverage of the Northern Hemisphere sky, ZTF provides an ideal dataset for this search. We present methods used in a systematic search for self-lensing signatures in Galactic binaries, and final candidates that may exhibit these signatures. This method could become a new means of discovering noninteracting compact binaries and provide a way to estimate their masses.

Massive stars place powerful constraints on stellar evolution and are observed in a menagerie of exotic evolutionary phases. These objects play a crucial role in regulating their environments. They drive the chemical evolution of their host galaxies, and set the energy balance of their surroundings via feedback processes. Due to the importance of massive stars, placing constraints on their evolution serves as a key to understanding galactic ecosystems. Notably, stellar variability is a powerful probe of the poorly-constrained physics of massive star evolution. In particular, variability studies on ensembles of evolved massive stars can significantly constrain stellar evolution. We aim to understand the variability of hot massive stars through a census of these objects. We accomplish this using data from the Gaia mission, cross-matched with light curves from the Zwicky Transient Facility (ZTF). We expect to characterize the evolution of massive star variability timescales and amplitudes along the main sequence and beyond. Our results will place key constraints on the evolution of massive stars. 

The Circumgalactic Medium (CGM) is an extended structure surrounding galaxies, populated with hot diffuse gas and cold dense clouds of gas. The CGM acts as an intermediary between gas within galaxies (Interstellar Medium, or ISM) and gas between galaxies (Intergalactic Medium, or IGM). Insights into its properties and behavior could lead to a connection between the CGM and galaxy evolution, and the transition of a galaxy from star-forming to non-star-forming (quiescent). One standard method of observing the CGM is by measuring the absorption of light by elements in the CGM along its path to Earth, and since elements ionized to different degrees have distinct absorption signatures that can be observed, we can use them to determine the properties of the cool CGM. Our project aims to determine how the radiation from two sources of radiation—the central galaxy and the background—affect the ionization of this gas. Using observational data from the Hubble Space Telescope, we aim to constrain the dominant ionization mechanism of the cool CGM by comparing the data to physically-motivated fits and theoretical models developed by Dr. Faerman and Prof. McQuinn. Preliminary results show that by relating the density of CGM gas to the star-formation rate in the galaxy, the model is more consistent with the data, suggesting a relationship between the two properties. We are currently testing our method with one specific, well-modeled galaxy sample, and our framework allows including other existing samples as well as new, future observations. Modeling the properties of the CGM and how it interacts with galaxies will help us understand how galaxies form and evolve over cosmic times; one of the great open questions in modern astrophysics.

 The Circumgalactic Medium (CGM) refers to the vast outer regions of gas within the gravitation influence of a host galaxy. The CGM contains a significant amount of gas flowing into and out of the host galaxy; transitions such as HI and OVI are frequently observed in absorption along quasar sightlines that pierce the CGM within close projected impact parameters. Absorption feature properties such as column density and central wavelength can provide insight into the content and kinematics of the CGM. Our research team, known as the Werk SQuAD (Student Quasar Absorption Diagnosticians), is currently assessing the two-dimensional distribution of gas in the CGM around galaxies with a redshift value of less than 0.65. We use measured gas column densities from the Hubble Space Telescope’s Cosmic Origins Spectrograph quasar absorption spectra and a program called GALFIT to measure galaxy inclination and azimuthal angles, to help us understand these kinematics relative to their orientation to the background quasar. All host galaxies have redshifts measured spectroscopically by the Werk SQuAD as part of the CGM2 survey. In particular, the galaxy inclination angle, combined with the quasar azimuthal angle and absorption-line column densities provide a measure of the extent to which gas flows concentrate along the major or minor axes of galaxies (along the disk of the galaxy or flowing near or away from the galactic center). Here, we examine trends in the CGM with quasar azimuthal angles and ion column densities. Ultimately, our goal is to further understand the physical interdependence of the gas that flows through the CGM and galaxy evolution.

Active galactic nuclei (AGN) found at the center of galaxies are a compact region of space that produce significantly higher than normal luminosity. AGN are powered by the accretion of matter into a supermassive black hole and sometimes present winds called outflows. Whether outflows affect the evolution of their host galaxies is still a topic of research. Outflows with speeds of more than 10% the speed of light, called Extremely high-velocity outflows (EHVOs), have not been thoroughly explored, and due to their large energies, they might play a large role in star formation. In the 16th data release of the Sloan Digital Sky Survey, 98 new quasars with EHVOs were identified. With this new sample, I will present the results of my findings on the following questions: (1) What does the average EHVO quasar look like? (2) Do these extreme outflows vary more or less than other previously explored outflows? (3) Can we detect these EHVOs at higher speeds? To answer the first question, I will present a composite of the 16th data release EHVO cases found. To analyze if they vary more often or less than other EHVOs, I will present the results of a longitudinal variability study on the 51 cases that were observed on multiple occasions in the EHVO sample. For the last question, I will show the results of applying code our team has created to remove the Lya lines from our spectra, so the intrinsic ions (such as NV, Lya, OVI) will be easier to analyze at higher speeds.

My project studies Extremely High Velocity Outflows (EHVO) in Quasars. Quasars are particularly interesting due to the fact that they are one the most luminous cosmological objects that we have observed in the universe. They are systems at the centres of galaxies that host supermassive black holes--which have masses that range from millions to billions of solar masses--surrounded by an accretion disk of superheated plasma, gas, and dust. The phenomenon that we are studying are the EHVOs in quasars, which are gas outflows traveling at above 10% of the speed of light from the active central region. My project attempts to answer the question of whether quasars with EHVOs show distinct physical characteristics when compared to Broad Absorption Line Quasi-Stellar Objects (BALQSOs), which are quasars with outflows that show a broad absorption width but at lower outflow speeds, as well as compared to the general parent sample of quasars. We hypothesized that quasars with EHVOs show distinctive physical characteristics when compared to the other quasar categories. To study quasar physical characteristics to test our hypothesis, we used data from the Sloan Digital Sky Survey (SDSS) in the latest data release. Previously, our group has found the measurement values for all quasar samples to be overestimated. Thanks to data provided in Rankine+2020, we developed software and used the data to cross-correlate the values of physical parameters, such as bolometric luminosity (Lbol), Eddington ratio and black hole mass (Mbh). I will present the preliminary results of the analysis on EHVO quasar’s physical properties when compared to BALQSOs and the parent sample. These results suggest that quasars with EHVOs exhibit larger values of their Lbol and Eddington ratio when compared to the other two classes of quasars, while the Mbh parameter does not show significant differences.


 

Much of cosmology, including the age, shape, and evolution of the universe, depends upon the values of certain parameters. The Hubble Constant is one such parameter and is currently undergoing thorough investigation: our two primary means of measuring it yield two conflicting values. Is this merely a series of errors, or is there new physics to be uncovered? In order to eliminate measurement error as an explanation, we need to reduce uncertainty, but our current methods of measuring the movement of distant galaxies are unlikely to yield the necessary precision. Instead, we are developing a new method that may be able bypass the current reliance on a series of calibrations. Fast Radial Bursts are sufficiently point-like to detect the curvature in their wavefronts; hence the time delay registered between several satellites a sufficient distance apart can be used to determine the curvature of the pulse and hence the distance to the burst. More precise measurements of the distance to Fast Radio Bursts will lead to a better measurement of the Hubble Constant and the evolution of the dark energy. Further, using radio telescopes will require minimal advancement in precision measurement given already active GPS methods. While exploring what configuration will yield the greateat sensitivity, I have found a particular equidistant configuration of satellites that is able to maintain a consistent range of error regardless of what direction the FRB signal is coming from. Currently I am extending this search to additional satellites and numerous FRB sources to show that our model is able to achieve sub-1% precision in the Hubble Constant. If so, our model could be used to resolve the Hubble Tension, or to show that new physics such as new behaviors in dark energy is in fact present.