Abstract: Meeting ID: 932 0300 1150

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Meeting ID: 932 0300 1150
Find your local number: https://ucsd.zoom.us/u/aydAfQdjx

We are reserving our first CASS Seminar slot, Friday, October 1, 3:00 PM, for a general meet-and-greet. We will conduct this remotely (via Zoom). I encourage all of those associated with, or interested in, CASS, from any Department at UCSD or SDSU, to attend. I especially encourage new students and postdocs to attend. We will introduce ourselves and say (in a sentence or two!) what our interests are in the grand astrophysics enterprise, from elementary particle physics to biochemistry.

 Abstract: Meeting ID: 974 2591 2411
Password: 871087

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Meeting ID: 974 2591 2411
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ABSTRACT: Black holes form at the centers of galaxies in the young Universe and, over the next 13 billion years, they grow together by factors of a million or more in mass. This growth generates energy that can affect galaxy evolution, including that of the Milky Way galaxy in which we live. In this talk, I describe how recent “wedding cake” X-ray+infrared+ optical surveys of the sky have led to a quantitative description of black hole growth over the last ~12 billion years. Most Active Galactic Nuclei are heavily obscured and thus look like inactive galaxies in optical surveys, so our census effectively quadruples the amount of accretion, and thus the amount of energy deposited in AGN host galaxies. However, contrary to leading models, our data suggest that for only a minority of galaxies does merger-triggered AGN “feedback” cause rapid quenching of star formation.

 Abstract: Meeting ID: 977 6510 0998
Password: 834402

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Meeting ID: 977 6510 0998

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ABSTRACT: The shapes and abundance of dark matter halos are directly tied to the fundamental physics of dark matter particles such as its free streaming-length and self-interaction cross section, and have thus proven to be essential probes of this otherwise elusive form of matter. Traditional measurements of the shapes and abundance of dark matter halos rely on observations of stars and galaxies which form within them. Such measurements become difficult at low halo masses, as galaxy formation becomes increasingly suppressed. Thus tests of dark matter at low halo-mass scales require a tracer which does not rely on the presence of stars. We have shown that strong gravitational narrow-line lensing provides a powerful probe of the presence of low mass structure in a much larger sample of systems than was previously possible, and enables the detection of dark matter halos well into the regime where the majority of halos are expected to be dark. I will present our results placing limits on a turnover in the halo mass function and measuring the low-mass end of the halo-mass concentration relation. I will also describe our upcoming JWST program to measure cold-torus flux ratios, and conclude by looking to the future for the next generation of instruments, telescopes, and surveys which will enable us to expand the narrow-line method to an order of magnitude larger sample.

 Abstract: Meeting ID: 930 9234 0612
Password: 963869

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Meeting ID: 930 9234 0612
Find your local number: https://ucsd.zoom.us/u/ac2WWeSjcg

ABSTRACT: The long-awaited James Webb Space Telescope is planned for launch on Dec. 18, 2021. With its 6.5 m deployable primary mirror, and cameras and spectrometers covering 0.6 to 28 µm, it promises extraordinary improvements in observing capabilities. Webb will be able to observe the first objects that formed after the Big Bang, the growth of galaxies, the formation of stars and planetary systems, individual exoplanets through coronography and transit spectroscopy, and all objects in the Solar System from Mars on out. It could observe a 1 cm2 bumblebee at the distance of the Moon, in reflected sunlight and thermal emission. I will review the observatory capabilities and planned observing program, and illustrate the history of the concept from 1988 to now. The Webb is a joint project of NASA with the European and Canadian space agencies.

 Abstract: Meeting ID: 951 5072 1516
Password: 167826

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Meeting ID: 951 5072 1516
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ABSTRACT: Over last six years, the LIGO-Virgo detections of gravitational waves from compact binary mergers have underlined their promise as an independent and powerful tool to explore the Universe. Nevertheless, the electromagnetic observation of the counterparts of GW sources provides different and complementary information about the binary systems, and therefore the combination of `multimessengers' is expected to lead to significantly enhanced science outcomes. In this talk, I will discuss what we learned in cosmology, nuclear physics, and heavy-elements production from LIGO-Virgo observations. I will then discuss the future aspects and challenges in these areas.

 Abstract: Meeting ID: 934 7314 1628
Password: 114007

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Meeting ID: 934 7314 1628
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ABSTRACT: Binary stars are foundational to modern astrophysics. They underpin precision measurements of stellar structure, age, and composition; they provide the most stringent tests of general relativity, they make possible the study of faint and rare objects such as black holes and neutron stars, and they are the progenitors of gravitational wave sources. The components of binaries often interact, dramatically changing their evolution and giving rise to a spectacular zoo of astrophysical phenomenology. To understand stars -- particularly massive stars -- it is necessary to understand binaries. Large-scale stellar surveys such as Gaia, TESS, and SDSS-V are transforming the binary field, making possible both comprehensive population demographics and the discovery of rare objects. I will discuss new insights gleaned from surveys in recent years, including the creation of stripped-envelope stars following binary mass transfer, the formation of equal-mass "twin" binaries in circumbinary disks, the metallicity-dependence of the binary fraction, and the discovery of planets in binaries. I will focus in particular on the search for dormant stellar-mass black holes in binaries, discussing recent candidates and the path forward to characterizing the detached black hole population.

 Abstract: Meeting ID: 916 9624 3727
Password: 351634

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Meeting ID: 916 9624 3727
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ABSTRACT: Understanding how galaxies form and evolve has been one of the most important topics in astrophysics.

In the past two decades, astrophysicists have realized that the so-called feedback mechanisms which regulate mass and energy into and out of galaxies play a fundamental role in driving galaxy evolution.

In this talk, I will first introduce the current challenges of understanding the physics of feedback and demonstrate that the properties of gas around galaxies, the circumgalactic medium (CGM), are essential to overcome these challenges. I will present my research that probes the CGM by utilizing the power of statistical analysis applied to big datasets of large sky surveys. The results have motivated not only new theoretical investigations of galaxy evolution astrophysics but also the development of new sky surveys. Finally, I will discuss the potential of combining machine learning techniques and big data to reveal new astrophysics of galaxy evolution in the upcoming era of large sky surveys.

 Abstract: Meeting ID: 917 8770 9095

Password: 573071

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Meeting ID: 917 8770 9095
Find your local number: https://ucsd.zoom.us/u/abM2GawX0g

ABSTRACT: For planet formation to be an empirical science we need to detect planets while they are still young and feeding from their parent circumstellar discs. Direct imaging of planets provides the way forward. We review imaging observations from ultraviolet (HST) to infrared (VLT, Gemini) to millimeter (ALMA) wavelengths and what they imply about the formation of Jupiters and Super-Jupiters. Classic ideas of dynamical friction, gravitational instability, and Bondi accretion are finding new applications.

 Abstract: Meeting ID: 999 8257 6466
Password: 789831

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Meeting ID: 999 8257 6466
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ABSTRACT: What are the mysterious sources of the most energetic particles ever observed? What astrophysical sources produce very energetic neutrinos? How do particles interact at extreme energies? Building on the progress achieved by the ground-based observations we are developing space and sub-orbital missions to answer these questions. The Extreme Universe Space Observatory (EUSO) on a super pressure balloon (SPB) is designed to detect ultrahigh energy astroparticles from above. EUSO-SPB1 flew in 2017 with a fluorescence telescope. EUSO-SPB2 is being built to observe both fluorescence and Cherenkov from ultrahigh energy cosmic rays (UHECRs) and neutrinos. These sub-orbital missions lead to POEMMA, the Probe Of Extreme Multi-Messenger Astrophysics, a space mission designed to discover the sources of UHECRs and to observe neutrinos above 20 PeV from energetic transient events. POEMMA will open new Multi-Messenger windows onto the most energetic events in the Universe, enabling the study of new astrophysics and particle physics at these extreme energies.

 Abstract: Meeting ID: 930 4660 4032
Password: 049478

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Meeting ID: 930 4660 4032
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ABSTRACT: The atmospheres of exoplanets provide a unique probe to studying the chemical diversity of exoplanet systems. Established observing techniques like transmission spectroscopy can provide information about the atmospheric spectrum, which can be better constrained using a combination of both high and low resolution data. Low resolution transmission spectroscopy efforts have produced many interesting results but largely rely on pre-existing instruments that are limited in the photometric precision that can be achieved over the duration of an exoplanet transit. Here I present the High-efficiency Instrument for the Rapid Assessment of eXo-atmospheres (HIRAX) that offers a different approach to performing transmission spectroscopy by using multiple narrowband filters to simultaneously image an exoplanet transit in multiple 3Å bandpasses. The high throughput of HIRAX and its imaging-based design is expected to offer an efficient path towards a survey of alkali lines in hot Jupiter atmospheres. A three bandpass version of HIRAX was recently funded and work is underway to optimize the instrument design for transmission spectroscopy of the sodium doublet (5889.9Å and 5895.9Å) to test on the Hale telescope at Palomar. In this presentation, I will discuss the motivation for HIRAX, the current instrument design, challenges, and future science observing plans. Finally, I will provide an update on the Keck Planet Finder (KPF), which is a stabilized R~95k Doppler spectrometer for the Keck I telescope being commissioned this summer. KPF science capabilities include high resolution transmission spectroscopy, which can be used to study sodium and complement the HIRAX low resolution data.

 Abstract: Meeting ID: 952 2362 9677
Password: 351073

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Meeting ID: 952 2362 9677
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ABSTRACT: I will discuss insights from analytic and numerical models of galactic chemical evolution and observations of Milky Way elemental abundances from the Sloan Digital Sky Survey's APOGEE project. Under generic model assumptions, abundances and abundance ratios do not change continuously but approach an equilibrium in which element production from nucleosynthesis is balanced by element depletion from star formation and outflows. APOGEE observations show that the distributions of stars in (magnesium,iron,age)-space change steadily across the Milky Way disk, with features that suggest radial migration of stars and complexity in the Galactic star formation history. However, the median trends of abundance ratios are remarkably stable throughout the disk and bulge, which allows these trends to provide empirical constraints on supernova nucleosynthesis that are insensitive to uncertainties in other aspects of chemical evolution. A 2-parameter model that represents a star's abundances as the sum of a "core collapse supernova process" and a "Type Ia supernova process" can fit the ~15 elemental abundances measured by APOGEE to an accuracy of 0.01-0.03 dex for most Milky Way disk stars. The correlated star-by-star deviations from this model demonstrate the existence of multiple "hidden" dimensions of chemical enrichment, offering further insight on the physics of nucleosynthesis and the history of distinctive stellar populations.

 Abstract: Meeting ID: 947 4748 9631
Password: 471401

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Meeting ID: 947 4748 9631
Find your local number: https://ucsd.zoom.us/u/ada5Sl33Ws

ABSTRACT: Core-collapse supernova explosions (CCSN) are one possible fate of a massive star. Simulations of CCSNe rely on the properties of the massive star at core-collapse. As such, a critical component is the realization of realistic initial conditions. Multidimensional progenitor models can enable us to capture the chaotic nuclear shell burning occurring deep within the stellar interior. I will discuss ongoing efforts to progress our understanding of the nature of massive stars through next-generation hydrodynamic stellar models. In particular, I will present recent results of three-dimensional hydrodynamic massive star models including rotation evolved for the final 10 minutes before collapse. These recent results suggest that realistic 3D progenitor models can be favorable for obtaining robust models of CCSN explosions and are an important aspect of massive star explosions that must be taken into consideration. I will conclude with a brief discussion of the implications our models have for predictions of multi-messenger signals from CCSNe.

 Abstract: Meeting ID: 921 4526 8589
Password: 945763

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Meeting ID: 921 4526 8589
Find your local number: https://ucsd.zoom.us/u/abVtGkr0G

ABSTRACT: The past 25 years have revealed a diversity of exoplanets far beyond what was imagined from the limited sample in the Solar System. With new and upcoming observing facilities and a rapidly growing number of nearby planets, we are poised to bring this diversity into focus, with detailed follow-up characterization of the planets’ atmospheres. In this talk, I will discuss two frontier topics in exoplanet atmosphere studies: (1) what can we learn about giant planets' origins from their present-day atmospheres? and (2) what can we learn about habitability from “Earth cousins”, planets that are a little bigger or a little hotter than the Earth? Finally, I will conclude with my outlook on the search for biosignatures in the atmospheres of potentially inhabited planets.

 Abstract: Meeting ID: 998 7875 4586
Password: 258605

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Meeting ID: 998 7875 4586
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ABSTRACT: Since the launch of Kepler in 2009, the field of stellar astronomy has been radically changed by the advent of long-duration, high-precision optical light curves. With the TESS mission we now have space-based light curves for millions of nearby stars, which allow e.g. precise characterization of stellar rotation periods, and enormous catalogs of flares. I'll review some of the transformative discoveries this data has enabled, and highlight exciting opportunities for stellar astronomy in the coming decade.

 Abstract: Meeting ID: 981 0207 6419
Password: 547625

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Meeting ID: 981 0207 6419
Find your local number: https://ucsd.zoom.us/u/a39VMgn4g

ABSTRACT: Type Ia supernovae (SNe Ia) are thermonuclear explosions of carbon/oxygen white dwarfs (WDs). Perhaps surprisingly to researchers outside the SN subfield, fundamental questions persist regarding any further details. What is the nature of the companion(s) that trigger the explosion? What mode of burning consumes the WD? And is one model responsible for all SNe Ia, or do multiple scenarios contribute to the overall population? In this talk, I will describe our theoretical and observational work on the "Dynamically Driven Double Degenerate Double Detonation" (D6) scenario, in which the coalescence of a double WD binary leads to a converging-shock-triggered detonation in the more massive WD and a subsequent SN Ia. Our recent successes, which include the best match to the Phillips relation in the literature and the prediction and discovery of hypervelocity stars ejected from the Milky Way, provide evidence that the D6 scenario is the mechanism responsible for all non-peculiar SNe Ia.

 Abstract: Meeting ID: 969 6505 4987
Password: 704415

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Meeting ID: 969 6505 4987
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ABSTRACT: When we look up at the night sky, we see a static universe. However, observational surveys have revealed that our universe is dynamic with a myriad of transient events. One of the universe's most fascinating and fastest explosive transients to come to light over the past decade are fast radio bursts. While fast radio bursts are seemingly connected to highly-magnetized neutron stars and are among the most prolific transients to occur in nature, the precise origins of fast radio bursts remain uncertain. In this talk, I will discuss this population of transients and our quest to understand their origins, primarily through observational studies of their local and host galaxy environments. I will describe our ongoing campaigns with large ground-based telescopes and HST to build legacy samples of their environments and extract crucial information on their host stellar populations. I will also discuss upcoming upgrades to fast radio burst experiments which will provide a flood of new, well-localized discoveries in the near future.

 Abstract: Meeting ID: 945 2529 3543
Password: 294951

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Meeting ID: 945 2529 3543
Find your local number: https://ucsd.zoom.us/u/aeojJOTWu

ABSTRACT: The upcoming decades will present exciting opportunities to explore the physics of merging supermassive black holes from the multi-messenger perspective. The electromagnetic identification of dual and binary candidates with subsequent detailed follow-ups will become routine. Thus, a study of the small-scale environment hosting these events provides the necessary groundwork for future investigations. In this talk, I will highlight published results and ongoing work from our Keck OSIRIS AO LIRG Analysis survey, which probes the nuclear gas kinematics in nearby interacting galaxies and beyond in the context of gas feeding and feedback. I will also present a time-domain reverberation mapping study that examines the broad line region kinematics of accreting black holes on a much smaller scale. The power of high-resolution studies in dissecting how systems dynamically evolve will become indispensable for understanding the astrophysics of merging supermassive black holes as we enter an exciting era of astronomy with the imminence of the James Webb Space Telescope, 30-meter class telescopes, and beyond.

 Abstract: Meeting ID: 980 0578 4755
Password: 152827

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Meeting ID: 980 0578 4755
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ABSTRACT: Galaxy clusters are filled with hot, diffuse X-ray emitting plasma, with a stochastically tangled and intermittent magnetic field whose energy is close to equipartition with the energy of the turbulent motions. In the cluster cores, the temperatures remain anomalously high compared to what might be expected considering that the radiative cooling time is short relative to the Hubble time. While feedback from the central active galactic nuclei is believed to provide most of the heating, there has been a long debate as to whether conduction of heat from the bulk to the core can help the core to reach the observed temperatures, given the presence of tangled magnetic fields. To address the problem of thermal conduction in a magnetized and turbulent plasma, we have created a replica of such a system at the National Ignition Facility laser, the largest laser laboratory in the world. Our data show a reduction of local heat transport by two orders of magnitude or more. While the diffusive transport of the highest energy charged particles appears to be unaffected by the spatial intermittency of the magnetic field, the diffusion of lower energy electrons is, instead, better described in terms of percolation. This, together with a cooling instability, leads to strong temperature variations on small spatial scales, as also observed in the intergalactic plasma. We conclude the talk describing new Machine Learning techniques that can be used to infer effective transport coefficient from experimental data or simulations.

 Abstract: Meeting ID: 930 5727 4155
Password: 316009

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Meeting ID: 930 5727 4155
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ABSTRACT: Our Galaxy teems with stars and their planets. The evolution of the two are intimately linked: stellar high energy radiation is thought to drive atmospheric evolution in close-orbiting exoplanets. However, studying their evolution is challenging as most changes occur on million-to-billion year timescales. I will discuss two complementary avenues in the study of stellar and exoplanetary evolution. I will examine the evolution of spin and magnetism in M dwarf stars, the smallest and most common type of star in the Galaxy and the most promising stars for the study of temperate planets. I will then turn to the discovery and characterization of young exoplanets, which may still be in the throws of dynamical and atmospheric evolution.

 Abstract: Meeting ID: 984 3684 9881
Password: 882388

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Meeting ID: 984 3684 9881
Find your local number: https://ucsd.zoom.us/u/aBg4niMYU

ABSTRACT: Using astronomy as a backdrop, this presentation will provide an overview of federal spending for science agencies, namely NASA and NSF, from formulating budgets in the Executive Branch to crafting appropriation bills in Congress. Ambitious science policies and the desire to maintain U.S. competitiveness in research fields help drive support for science funding. However, politics, competing priorities, and fixed funding caps factor into the fight for taxpayer dollars. The objectives of the presentation are to provide a better understanding of the funding landscape that impacts science budgets, demystify the decision-making process, and offer some insight on effectively communicating with Congress on science funding.

 Abstract: Meeting ID: 980 7200 1104
Password: 963253

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Meeting ID: 980 7200 1104
Find your local number: https://ucsd.zoom.us/u/ab1PGoNvr7

ABSTRACT: The current era of astronomical observations, Solar System exploration and powerful supercomputers is bringing new insights to the origin of planetary systems. I will focus on the origin of planetesimals, primordial minor planets with sizes ~10 km. These are the least massive gravitationally bound objects in the universe, and their origin is crucial to understanding our Solar System and extrasolar planets. I will describe current ideas for how particle growth crosses the daunting ``meter size barrier” where collisions tend to be destructive and solids can drift rapidly into the host star. I will describe the Steaming Instability, a mechanism that can concentrate pebbles (large dust) to high densities in the disk midplane, triggering planetesimal formation by the gravitational collapse of these pebbles. I will describe how these theories relate to recents observations of protoplanetary disks by ALMA and to the study of the Kuiper belt by telescopes and by the New Horizons mission.

 Abstract: Meeting ID: 963 0749 3368
Password: 163874

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Meeting ID: 963 0749 3368
Find your local number: https://ucsd.zoom.us/u/adIBRhyyff

ABSTRACT: Core-collapse supernovae are among the most spectacular and efficient neutrino factories known so far. Detection of these neutrinos allows us to probe physics in extreme conditions not accessible on Earth. But so far, even with the detection of about twenty electron antineutrinos from SN 1987 A, we are yet to test even the most basic prediction about the neutrino emission, i.e., different neutrino flavors produced during the collapse share a comparable amount of the released energy. Existing detectors can register significantly more neutrinos of all flavors from the closeby core-collapse supernova and test this assumption. Unfortunately, this extreme phenomenon rarely occurs in our galaxy and its vicinity, only a few times per century.

What is more, while the multichannel detection of the next nearby supernova undoubtedly will allow us to measure and infer certain pieces of information, these will be solely about a single star. Theoretically, we expect a lot of common features, but nature may surprise us. Because of that, it is essential to observe neutrinos from multiple supernova events – the diffuse supernova neutrino background (DSNB).

The Super-Kamiokande (SK) detector achieved the most stringent upper limit on the electron antineutrino component of the DSNB. This limit is only a factor of 2-3 above most of the theoretical predictions. In addition, SK is now enriched with gadolinium which will help to reduce backgrounds for the DSNB search and most probably lead to the detection within the near future. The electron neutrino component of the DSNB has a ten times weaker upper limit than the electron antineutrino component. But with the upcoming Deep Underground Neutrino Experiment (DUNE), the limit may change into observation. As impressive as it sounds, capturing the complete picture of the core-collapse supernova landscape and investigating new astrophysics or physics requires probing DSNB in all flavors. But the upper limits on the non-electron component of the DSNB (muon and tau neutrinos and antineutrinos) are approximately a thousand times weaker than the theoretical predictions.

In this talk, I will present how the large-scale direct dark matter detectors can help significantly tighten the upper limits on the non-electron component of DSNB. In addition, I will talk about plausible beyond the Standard Model scenarios, which could alter the non-electron neutrino emission from the core-collapse supernovae.

 Abstract: Meeting ID: 997 2560 2137
Password: 511878

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Meeting ID: 997 2560 2137
Find your local number: https://ucsd.zoom.us/u/abYYKmcgwb

ABSTRACT: Since ALMA began operations in 2015, we have been availed of a plethora of resolved millimetre images of protoplanetary discs. We have realised that substructure in these discs, such as rings, spirals and gaps, are the norm rather than the exception. In this talk, I explain the state of the field and highlight recent developments, particularly the move away from using continuum images to infer the underlying properties of the disc, and instead relying on kinematic detections of substructure. In particular, I will discuss the role that gravitational instability plays in the observation of spiral features.

 Abstract: Meeting ID: 986 1521 7231
Password: 953499

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Meeting ID: 986 1521 7231
Find your local number: https://ucsd.zoom.us/u/adZa9JO972

ABSTRACT: Massive galaxies like the Milky Way and Andromeda (M31) form in part from the accretion of less massive galaxies. The chemical and dynamical properties of disrupted galaxies, in the form of streams and shells in the stellar halo, provide a record of this hierarchical assembly process. M31 is particularly crucial for modern near-field cosmology. Owing to its proximity, its stellar halo can be resolved into individual stars like the MW, yet simultaneously be observed from a global perspective like external galaxies. Moreover, achieving a complete understanding of M31's active merger history has broader significance for galaxy evolution, where its disk may have survived a major merger within the last few billion years. In this talk, I will present results from spectroscopic surveys of resolved stellar populations in M31's giant stream, shells, and phase-mixed stellar halo using the DEIMOS instrument on Keck. I will discuss the implications of chemodynamical analyses of these structures for M31's formation history, focusing on the question of a recent merger scenario. Lastly, I will address how M31 will connect the Local Group to the Local Volume in the era of the Roman Space Telescope and ELTs.