Date: Wednesday 07-Feb-2024
Speaker: Dr. Igor Andreoni - University of Maryland
Title: Uncharted territories in optical time-domain astronomy
The night sky is ever changing at all time scales. Historically, only bright transient sources that remain observable for weeks or months have been studied intensively, as opposed to faster and dimmer ones. However, we are witnessing a paradigm change with modern wide-field surveys, such as the Zwicky Transient Facility (ZTF), which enable the systematic identification of transients evolving on time scales as short as a few hours - or even several minutes. New telescopes and data processing techniques present us with unprecedented opportunities to probe the optical time domain. In this colloquium, I will show how Vera C. Rubin Observatory LSST will be used to target fast, faint, rare transients currently eluding our searches. I will then present a novel survey that I am conducting with ZTF in a newly developed observing mode, which allows us to observe bright sources with a time resolution as good as 6 milliseconds, over a 47 sq. deg. field of view. This is a remarkable change compared to the > minutes time scales that can be sampled in standard observing mode. The journey in uncharted regions of the luminosity vs time-scale parameter space of optical transients has just begun.
Date: Wednesday 14-Feb-2024
Speaker: Dr.Jinyi Yang (University of Arizona)
Title: Probing the Early Universe Using the Most Distant Quasars
Quasars at z~7 hosting highly accreting black holes are unique probes for the early Universe, including the growth of the earliest supermassive black holes (SMBHs), the assembly of their massive host galaxies, and cosmic reionization. I have been leading a distant quasar survey, which yielded the largest sample of luminous quasars at z~6.5-7.6. Pre-JWST, studies using this sample have placed stringent constraints on early SMBH growth and the intergalactic medium (IGM) evolution. The launch of JWST opens up a new era. I will introduce my recent effort to conduct high-resolution observations of a sample of ~30 luminous z~7 quasars using JWST and ALMA, in synergy with observations in other wavelengths. This dataset allows us to delve into a comprehensive study of the interactions between early SMBHs and their host galaxies at multiple scales and phases, and enables new methods to constrain the reionization physics. I will present early results, covering early SMBHs, AGN feedback, host galaxy stellar emission, and IGM evolution. These new discoveries mark the beginning of a new era towards understanding the formation of early SMBHs, the assembly of massive host galaxies, and reionization history. With the upcoming next-generation surveys and facilities, the next decade.
Date: Wednesday 21-Feb-2024
Speaker: Dr. Feige Wang (University of Arizona)
Title: Growing Early Supermassive Black Holes in a Cosmological Context
The existence of luminous quasars, powered by supermassive black holes (SMBHs) when the Universe was less than 800 million years old, challenges our understanding of SMBH formation. In the hierarchical structure formation ontext, an assortment of cosmological simulations can produce these massive SMBHs, starting with massive seeds and growing within the most biased dark matter halos situated in overdense regions. However, rigorously testing these theories remains challenging. To address this, I developed the ASPIRE program, which provides a legacy galaxy redshift survey along the line-of-sights of distant quasars with JWST slitless spectroscopic and ALMA mosaic observations. This program also involves Chandra, HST, VLA, and ground-based optical and infrared follow-up observations. In this talk, I will demonstrate our ability to finally resolve the long-standing question of whether the earliest supermassive black holes (SMBHs) reside in the most massive dark matter halos and to probe early SMBH growth in a cosmological context using ASPIRE data. Additionally, I will highlight ASPIRE as a treasury program for understanding cosmic reionization, galaxy formation, and metal enrichment in the early Universe. Finally, I will illustrate that we are entering an exciting new era in our understanding of the formation of SMBHs and galaxies in the early Universe, leveraging the unprecedented sensitivity of JWST and upcoming state-of-the-art facilities such as AXIS, Roman, Rubin, and extremely large telescopes.
Date: Wednesday 28-Feb-2024
Speaker: Dr. Adina Feinstein - University of Colorado
Title: A Tale of Planetary Adolescence and Evolution
Within the past decade, we have discovered only a dozen young (< 300 Myr) short-period exoplanets, compared to ~5,600 mature exoplanets. The radii of these young planets are larger than older planets on similar orbital periods. The leading hypothesis is that these young planets have inflated atmospheres because they are still contracting. Inflated atmospheres are more susceptible to photoevaporation -- atmospheric removal driven by high energy stellar irradiation. These effects are intensified in the earliest stages of planetary evolution, when young stars are more active and produce extreme levels of X-ray and Ultraviolet (UV) radiation on a variety of timescales. Even though it is challenging to study exoplanets around active stars, observational constraints of these targets provide crucial insights into our understanding of exoplanet formation and evolution. In this talk, I will present several benchmark studies of young stars and their planets spanning from the UV to the infrared (IR). I will present the results of several large statistical surveys of stellar flares with the Transiting Exoplanet Survey Satellite, and detailed characterization of stellar flares with the Hubble Space Telescope. I will present atmospheric follow-up characterization of young short-period exoplanets in the optical, near-IR, and IR. Finally, I will present models of flare-driven atmospheric escape, discuss the contributions of stellar flares in removing gas-dominated planetary atmospheres, and highlight future steps in understanding these challenging young systems.
Date: Wednesday 06-Mar-2024
Speaker: Dr. Michael Koss (Eureka)
Title: Merging Black Holes in Merging Galaxies: Using Multi-Wavelength Observations to Constrain the Prequel to Gravitational Waves
Massive black holes (MBHs), up to billions times more massive than the sun, lurk at the hearts of essentially all galaxies. One of the most efficient ways to grow these BHs is through mergers of galaxies, during which tidal interactions funnel large amounts of gas to the galaxies’ centers, to feed the MBHs. Eventually, the dual MBHs may collide, releasing gravitational waves and potentially forming recoiling MBHs that may escape the merger remnant. While several future GW facilities are designed to chase these enticing high-amplitude and low-frequency signals through cosmic history, most other parts of this astrophysical story are yet to be corroborated by observations, even in the nearby universe. I will present recent and on-going efforts to identify and survey the population of merging MBHs in merging galaxies, pursued with observations across the electromagnetic spectrum. I will focus on high-resolution observations using both large ground-based telescopes with “adaptive optics'' and space-borne telescopes, which have enabled the identification of dual MBHs, and their links to powerful/enhanced accretion. New and upcoming facilities, including JWST, ALMA, TMT, and Rubin, promise to find many more such systems and to eventually link the complex astrophysics to fundamental gravitational physics.
Date: Wednesday 13-Mar-2024
Speaker: Dr. Kishalay De (MIT)
Title: Uncovering dust enshrouded cataclysms toward a census of stellar and black hole evolution
Multiplicity is ubiquitous in stars and the remnants they leave behind. While eruptive mass transfer has profound impacts on their long term evolution, the resulting processes are commonly enshrouded in dust produced by mass outflows, preventing direct observational constraints at optical/X-ray/UV bands. In pursuit of a complete census of the role of accretion outbursts in stellar and black hole evolution, I will present the WISE Transients Project (WTP) -- aimed at complete characterization of the variable mid-infrared sky that identified millions of new infrared variables in 15 years of data from the NEOWISE survey. I will highlight recent and ongoing work from the dataset revealing i) a missed population of dusty stellar mergers in our Galactic backyard, ii) new insights into the fiery fates of close planetary worlds, iii) the birth of black holes from dusty eruptions of stripped stars and iv) the growth of supermassive black holes via tidal captures of stars in Galactic nuclei. I will end with an overview of the exciting upcoming decade of infrared surveys that is poised to finally reveal a complete roadmap of stellar and black hole evolution.
Date: Wednesday 27-Mar-2024
Speaker: Dr. Megan Mansfield (University of Arizona
Title: Studying exoplanet atmospheres in the era of JWST
The recent launch of JWST is revolutionizing our understanding of exoplanet atmospheres by providing observations at an unprecedented level of detail. In this talk, I will discuss two methods for studying the atmospheres of exoplanets with JWST. First, I will discuss the potential for spectroscopic eclipse mapping with JWST. Spectroscopic eclipse mapping is the only observational technique which allows for simultaneous resolution of the atmosphere in three spatial dimensions: latitude, longitude, and altitude. I will present a spectroscopic eclipse map of the hot Jupiter WASP-18b, the first such map ever produced. Second, I will present a method of using JWST to quickly determine which M dwarf planets host atmospheres through secondary eclipse observations. I will give an overview of the application of this method in the first two years of JWST science, including new, unpublished results from my own program to observe the hot terrestrial planet Gl 486b in secondary eclipse. Finally, I will briefly discuss synergies between JWST and upcoming extremely large telescopes in studying exoplanet atmospheres.
Date: Wednesday 03-Apr-2024
Speaker: Dr. Aaron Pealman ( McGill Unuversity)
Title: Fast Radio Bursts: Illuminating their Origins in the Era of Wide-Field Radio Telescopes
Fast radio bursts (FRBs) are extremely energetic, millisecond-duration radio flashes that emanate from astrophysical objects located at cosmological distances. Although the high all-sky event rate (hundreds per sky per day) of FRBs suggest that they are produced by a common phenomenon in the Universe, their precise origins are currently unknown. The radio signals from FRBs encode valuable information about the intervening material through which they propagate, making them unique probes of the diffuse matter between stars and galaxies and the distribution of ionized baryons in the cosmic web. In this talk, I will give an overview of our current understanding of the enigmatic FRB phenomenon. I will discuss recent progress in the field using the wide- field digital transit radio telescope, Canadian Hydrogen Intensity Mapping Experiment (CHIME), which is being used as part of the CHIME/FRB project to detect hundreds of new FRBs each year. I will also describe the current status of the CHIME/FRB Outriggers project, which will expand upon CHIME/FRB’s detection capabilities and enable thousands of FRBs to be pinpointed on the sky to 50 milliarcsecond precision using novel synoptic very long baseline interferometric (VLBI) techniques. I will also present new results from a simultaneous X-ray and radio observational campaign of the closest known extragalactic repeating FRB source, FRB 20200120E, which resides in a ~10 Gyr-old globular cluster within the M81 galactic system and is serving as a Rosetta Stone for understanding the nature of a possibly exotic FRB source.
Date: Wednesday 10-Apr-2024
Speaker: Dr. Charlotte Olsen (CUNY)
Title: Exploring environment and galaxy evolution with dwarf galaxy star formation histories
Our understanding of galaxy evolution is often hindered by the complexity of the processes that drive it. Star formation offers a powerful tool for tracing galaxy growth, and star formation history (SFH) reconstruction techniques make this even more powerful by allowing us to probe backwards in cosmic time. With spatial information, we can test correlations within populations, pairs, and within regions of a galaxy. When studied jointly, correlations between SFHs can provide insights into large scale environmental influences, local feedback mechanisms, and other drivers of galaxy evolution. I will discuss how this analysis has led to surprising discoveries in Local Volume dwarf galaxies as well as showing work that leverages resolved observations to trace the build up of stars within galaxies. The demonstrated versatility of SFHs as a tool for exploring galaxy evolution makes the vast amount of data from the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) the perfect laboratory for learning how galaxies interact with their environment. We are currently using the state of the art NewHorizons simulation to predict how galaxy interactions with environment may be detected in LSST.
Date: Wednesday 17-Apr-2024
Speaker: Dr. Danielle Berg (University of Texas-Austin)
Title: Observational Benchmarks of Chemical Evolution from Extreme Emission Line Galaxies
The advent of the James Webb Space Telescope has opened our first window onto detailed abundance studies of high redshift (z > 6) extreme emission line galaxies. The coming years will provide the first spectroscopic samples of these galaxies in the epoch of reionization with which we can constrain their chemical compositions and histories and resulting conditions that shaped the escape of ionizing photons. As we build our samples of high-ionization nebular emission lines and absorption profiles of outflowing gas, we can begin to understand how the time-dependent nature of elemental production affects our interpretation of different epochs of galaxies and the resulting strung-together evolutionary story. I will present recent HST and JWST observations of the dynamic ISM across multiple epochs and the lessons we are learning about chemical evolution, star formation histories, and feedback prescriptions.
Date: Wednesday 24-Apr-2024
Speaker: Dr. Christine Chen (STScI)
Title: Exploring the Environments of Young Planetary Systems
Observations of debris disks provide unique insight into the environments in which planetary systems form and evolve. Debris disks are planetary systems containing planets, planetesimals, and dust. Collisions among these bodies produce observable secondary gas and dust which act as tracers for a host of processes with in the disk. JWST is revolutionizing our understanding of debris disks through exquisitely sensitive, high angular resolution near- to mid-infrared observations. I will present highlights from Cycle 1 programs including the discovery of (1) large, recent collisions in the archetypal beta Pic debris disk, (2) water ice in exo-Kuiper Belts, and (3) hot, florescent CO gas in young (<50 Myr old) debris disks. Together, these observations illustrate that debris disks are often dynamic environments that influence their planetary inhabitants and that observations of gas and dust inform our understanding of planetary and minor bodies within them.
Date: Wednesday 01-May-2024
Speaker: Dr. Frank van den Bosch (Yale University)
Title: New Insight into Cosmology and the Galaxy-Halo Connection from Non-Linear Scales
In our LCDM paradigm, galaxies form and reside in dark matter halos. Establishing the (statistical) relation between galaxies and dark matter halos, the `Galaxy-Halo connection', therefore gives important insight into galaxy formation, and also is a gateway to using the distribution of galaxies to constrain cosmological parameters. After a brief introduction to how clustering and gravitational lensing can be used to constrain the galaxy-halo connection, I show that several independent analyses all point towards a significant tension in cosmological parameters compared to the recent CMB results from the Planck satellite. I discuss the potential impact of assembly bias, and present satellite kinematics as a complementary and competitive method to constrain the galaxy-halo connection. After a brief historical overview of the use of satellite kinematics, I present a novel analysis, and show how it improves our knowledge of the galaxy-halo connection. I end with a re-examination of the cosmological tension, this time using satellite kinematics rather than gravitational lensi
Date: Wednesday 08-May-2024
Speaker: Dr. Nikole Lewis (Cornell University)
Title: Deep Reconnaissance of Exoplanet Atmospheres with JWST
With JWST a new window into exoplanet atmospheres is now wide open. Cycle 1 JWST observations of exoplanet hosting systems have already proven the power of this observatory to provide new and transformational insights into exoplanet atmospheres. Here I will focus on key results from JWST Cycle 1 programs that aimed to perform “deep” observations of specific transiting exoplanet hosting systems to explore the physics and chemistry at work in these planetary atmospheres. The JWST Telescope Scientist Team (JWST-TST) used 133 of Cycle 1 guaranteed observing time to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS) on three archetypical planets: a hot Jupiter (WASP-17 b), a warm Neptune (HAT-P-26 b), and a temperate Earth (TRAPPIST-1e). Through both transmission and emission observations spanning 0.6-12 microns, the DREAMS survey has uncovered new and unexpected chemistry at work in these atmospheres and allowed us to explore their three-dimensional atmospheric structure. I will additionally discuss complementary observations of additional transiting exoplanet targets with JWST, such as HD189733b, and the expansion of our wavelength coverage on key targets into the ultraviolet with Hubble. In this talk I will set the stage for the transformative exoplanet science being performed with JWST by providing a look at previous state-of-the art observations with Hubble and Spitzer for these targets. I will also look forward to future observations with JWST and Hubble that will continue our reconnaissance of these foundational targets.
