Session K02: Astrophysics

Unveiling the first seeds of supermassive black holes using cosmological simulations

Supermassive black holes are now believed to be at the centers of almost every massive galaxy in our Universe. Where and how did they form and grow to their observed masses (a million to tens of billion solar masses)? Unveiling the nature of their first "seeds" is a key science goal for current and future observational facilities such as JWST, LISA and Lynx. Predictions from cosmological hydrodynamic simulations are going to be crucial for using data from upcoming facilities to determine seeding mechanisms. However, current cosmological simulations cannot constrain seed formation because they are unable to properly resolve the seeds and their formation processes. I will talk about our recent works geared towards developing seeding prescriptions for the next generation cosmological simulations. Unlike current state of the art, these simulations would be able to distinguish between black holes originating from different seeding mechanisms. To start with, we have conducted a large systematic study using the highest resolution "zoom-in" cosmological simulations, which explores a range of black hole seeding prescriptions that depend on the gas properties within dark matter haloes. We seed black holes in nearly pristine star forming halos and investigate the impact of changing the minimum halo mass and star forming, metal poor gas mass thresholds on key observables such as black hole merger rates, masses and luminosities. The different seeding conditions leave strong and distinct imprints on the merger rates measurable by LISA. However, electromagnetic observations alone may find it difficult to discriminate between seeding channels. Finally, I will also discuss implications of our seeding models on the assembly of the highest redshift (z > 6) quasars. Overall, these results are going to provide a useful benchmark for continued development of black hole seeding prescriptions for large volume cosmological simulations.   

New Analysis of Cold Clouds in Perseus Spiral Arm

It is well known that stars form from the gravitational collapse of cold interstellar gas clouds within galaxies, but how such clouds themselves form remains up for debate. The origins and development of these clouds should therefore be investigated. Building on research by Sato (1990) and Hasegawa et al. (1983), we are investigating a section of the Perseus spiral arm. We are developing a new method of determining the abundance of cold hydrogen gas in this region, where passage through the arm may cause the clouds to evolve. Our approach compares cold atomic gas appearing as HI self-absorption (HISA), molecular gas traced by carbon monoxide (CO) emission, and thermal radiation from interstellar dust. We compare our results to Sato's and Hasegawa et al.'s to test and refine our analysis. Once our method is finalized, we will compare the gas properties (temperature, density, etc.) implied by different studies to assess how their analytic assumptions affect our knowledge of these clouds' evolutionary states and their prospects for future star formation.   

Tuning into planet formation: The tale of GJ 105.5

The Transiting Exoplanet Survey Satellite (TESS) has discovered over 5,000 planet candidates to date. One intriguing TESS sub-Neptune mass planetary candidate, GJ 105.5, has an orbital period of 15.669±0.002 days and a radius of 2.69±0.55 R_earth and orbits an adolescent K dwarf star. To both confirm the planet and constrain its mass, we obtain high-spectral resolution spectroscopy with ground-based observation with the iSHELL spectrograph at the NASA infrared telescope facility and the NEID spectrometer on the WIYN 3.5m telescope at Kitt Peak National Observatory from which we extract precise radial velocities (PRVs). Combining PRV measurements at visible and near-infrared wavelengths reduces the impact of star spots or other sources of stellar variability on the time series which can be misinterpreted as a planetary signal. In this talk, I will review the PRV method of exoplanet detection, the TESS mission, the observations obtained of this candidate planet thus far, the complex analysis needed to confirm its planetary nature, and our upcoming iSHELL and NEID observing programs. The addition of every planet with measured mass will benefit our understanding of planet formation, particularly in young systems.   

Characterizing the Shape of Solar Flares using Topological Data Analysis

Solar flares are eruptions of high energy radiation from the sun, which if powerful enough, can cause widespread blackouts and loss of communication. Prediction of these flares is essential to protect Earth’s electricity-based infrastructure.

The Atmospheric Imaging Assembly collects images of the Sun, taking images in seven different wavelengths – 94 Å, 131 Å, 171 Å, 193 Å, 211 Å, 304 Å, and 335 Å – repeating the cycle with a cadence of every 12 seconds. Flares are categorized by increasing intensity starting from A and going through B, C, M, and X classes. The Geostationary Operational Environmental Satellite has recorded solar emissions and their intensities for over a decade and using this data we are able to place flares into their classes.

Recently, there has been more interest in using Machine Learning (ML) techniques to predict occurrences of solar flares. ML based models are used to correlate various features extracted from solar flare data. We propose to apply Topological Data Analysis (TDA), a mathematical approach that studies the structures and shapes of datasets.

In this talk, we present a TDA-based approach to extract topological features of AIA images and topological features of flare intensity time series and discuss possible application for flare prediction problems.

    

Studying Variability in Blazars with Multiple Extraction Pipelines developed for the TESS Mission

Blazars are extreme examples of the Active Galactic Nuclei (AGN) phenomena. The blazar class of radio loud AGN are those oriented such that we are looking nearly down the throat of the relativistic jet, resulting in the observed emission being dominated by processes at work in the jet and being both amplified and time-compressed in our frame. The defining characteristics of blazars are a featureless or nearly featureless optical continuum, large amplitude and highly variable polarization, and large amplitude continuum variability at all wavelengths and on timescales ranging from minutes to decades. In this presentation, I compare blazar light curves produced from several different extraction pipelines to ground truth observations and to each other, with the goal of determining which pipeline most accurately corrects for background and other systematics.   

Simulations of SMBH accretion in isolated and merging galaxies with an explicit, multiphase ISM

We study gas inflows onto supermassive black holes using hydrodynamics simulations of isolated galaxies and idealized galaxy mergers with an explicit, multiphase interstellar medium (ISM). Our simulations use the recently developed ISM and stellar evolution model called Stars and MUltiphase Gas in GaLaxiEs (SMUGGLE). We implement a novel super-Lagrangian refinement scheme that increases the gas mass resolution in the immediate neighborhood of the black holes (BHs) to accurately resolve gas accretion. We do not include black hole feedback in our simulations. We find that the complex and turbulent nature of the SMUGGLE ISM leads to highly variable BH accretion. BH growth in SMUGGLE converges at gas mass resolutions ≤ 3000 M_?. We show that the low resolution simulations combined with the super-Lagrangian refinement scheme are able to produce central gas dynamics and BH accretion rates very similar to that of the uniform high resolution simulations. We further explore BH fueling by simulating galaxy mergers. The interaction between the galaxies causes an inflow of gas towards the galactic centres and results in elevated and bursty star formation. The peak gas densities near the BHs increase by orders of magnitude resulting in enhanced accretion. Our results support the idea that galaxy mergers can trigger AGN activity, although the instantaneous accretion rate depends strongly on the local ISM. We also show that the level of merger-induced enhancement of BH fueling predicted by the SMUGGLE model is much smaller compared to the predictions by simulations using an effective equation of state model of the ISM.   

GHz-Frequency Radio Surveys: The Premier Tool to Study Magnetic Activity at the Bottom of the Main Sequence

Ultracool dwarfs (UCDs) span the stellar and substellar regimes. Perhaps some of the most surprising discoveries among this class of objects are that they host strong, kG-strength magnetic fields and are powerful emitters of radio flares, despite their exoplanet-like effective temperatures and neutral atmospheres. However, many unanswered questions remain regarding their magnetic activity, including what are the characteristics of their magnetic dynamos, what is the nature of the electrodynamic engine that triggers magnetic reconnection to accelerate radio-emitting electrons, and what is the origin of the emitting plasma. Although UCD magnetic activity has been observed at radio, Hα, and X-ray wavelengths, UCD radio emissions alone can directly probe the magnetic field strengths and plasma environments of these objects. We present key results of radio surveys of UCD magnetic activity and explore the future prospects for addressing these lingering unanswered questions.