Date: Wednesday 31-Jan-2024
Speaker: Namrata Roy (Johns Hopkins University)
Title: Violent feedback-driven winds from high z Radio loud AGNs revealed by JWST
Abstract: Active galactic nuclei (AGN) feedback via radio jets play a dominant role in shaping massive galaxies across cosmic time. Despite the relatively short lifetime of a powerful jet (~ 10^7 yr), its enormous energy output can significantly impact the host galaxy. These jets can trigger shocks and also drive large-scale gas outflows through an expanding over-pressured cocoon. High redshift radio galaxies (HzRGs) are particularly interesting since they host the most extreme examples with powerful outflows. However, spatially resolving these ionized outflows in sub-kpc scale is extremely challenging for HzRGs. In this talk, I will show how JWST is starting to make groundbreaking progress in feedback studies by pushing resolved optical-IR observations towards higher redshift, with better sensitivity, greater angular resolution over a large wavelength window. I will present NIRSpec IFU observations of two fascinating HzRGs (z~4), which show radio lobes and large scale outflow signatures. One object shows a clear one-sided conical shaped ionized emission, with high gas velocities (exceeding 900 km/s) and extremely broad line profiles (line width ~ 1200 km/s). The outflowing ionized nebulae spatially overlaps with the brighter radio lobe, indicating that the extraordinary gas kinematics are driven by the radio jets. The second source, on the other hand, shows a very clumpy ionized gas morphology, with several distinct velocity components extending on both sides of the central AGN core. Our analyses show that the regions with the broadest line profiles exhibits the strongest mass outflow rates in these radio-AGN systems, with their integrated outflow rates exceeding most luminous quasars across redshifts. Our work is just beginning to scrape the surface of the HzRGs and their jet-ISM interplay. More such examples will help us to place these observations in the context of low redshift well-studied sample from the nearby universe.
Date: Wednesday 07-Feb-2024
Speaker: Digvijay Wadekar (Institute of Advanced Study)
Title: New black hole mergers from a search pipeline for gravitational waves with higher-order harmonics
Abstract: Currently, around 100 binary black hole (BH) mergers have been found in the LIGO-Virgo gravitational wave (GW) data, and upcoming surveys like Cosmic Explorer have the potential to detect BH mergers up to nearly the edge of the observable Universe. Nearly all of the current and previous GW searches include GW waveforms with only the dominant quadrupole mode, i.e., omitting higher-order harmonics which are predicted by general relativity. I will first show a new efficient method to include higher-order harmonics into a GW search pipeline (without drastically increasing the computational cost or substantially degrading the search sensitivity). I will then present detections of ~10 new black hole mergers in the previous LIGO-Virgo O3 data from our new pipeline. Some of the new BH binary detections have astrophysically interesting properties such as BH masses in the IMBH and pair-instability mass gap ranges, high-redshifts (1
Date: Wednesday 14-Feb-2024
Speaker: Niall Whiteford
Title: A Game Changing Spectrum: The First Deep-Dive Retrieval Analysis of VHS 1256 b
Abstract: VHS 1256 b, the young planetary-mass and highly variable companion, was observed as part of the High Contrast Imaging of Exoplanets and Exoplanetary Systems with JWST ERS program #1386. These observations combined NIRSpec and MIRI medium resolution spectroscopy, resulting in one of the most complete and highest quality SEDs to date for a world beyond our solar system. This is the first continuous spectrum of its kind, spanning 1 – 18 microns. Consisting of nearly 19,000 datapoints, it represents an order of magnitude jump from what has previously been possible – igniting a new era of possibilities and challenges for model fitting techniques. Using the Brewster retrieval framework, we have begun to thoroughly probe the dynamic chemical and cloudy state of VHS 1256 b’s atmosphere. We have detected the presence of Forsterite clouds, a surprising preference for uniform (non-patchy) clouds and the presence of NH3 at an earlier spectral type than previously seen for VHS 1256 b’s brown dwarf cousins. Here, we outline these novel results along with the crucial lessons learned in the first exploration of such a rich and complex dataset.
Date: Wednesday 21-Feb-2024
Speaker: Lucia Perez (Flatiron Institute, Princeton University)
Title: CAMELS-SAM and beyond: cracking open the galaxy-halo connection with machine learning
Abstract: While many advanced methods for the statistical analysis of cosmological data have been developed to handle the looming breadth of new astronomical observations, a common constraint is the availability of training cosmological simulation data, especially that which includes realistic galaxy formation physics and the volume and/or resolution necessary to match observations. CAMELS-SAM and its newest updates offer crucial and unique training data sets of realistic galaxies across an enormous range of cosmologies and galaxy physics formulations. As the larger-volume ‘hump’ of the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project, CAMELS-SAM uses semi-analytic models (SAMs) of galaxy formation to flexibly and quickly generate galaxies over 1000 dark-matter only simulations of L=100 h^-1 cMpc and N=640^3. We discuss new or upcoming expansions to CAMELS-SAM: the updated galaxy catalogs using the Santa Cruz SAM with 1) up to 9 varied astrophysical parameters, with 2) complete photometry generated for all galaxies; and, 3) new galaxy catalogs with the L-Galaxies SAM. These CAMELS-SAM datasets together will offer many possibilities for the next generation of simulation-based inference on observed galaxies.
Date: Wednesday 28-Feb-2024
Speaker: Colby Merrill (Cornell University)
Title: The Age of (152830) Dinkinesh I Selam Constrained by Secular Theory
Abstract: The age of the main-belt binary asteroid system, (152830) Dinkinesh, is constrained through secular dynamics assuming the secondary, Selam, is at equilibrium. Selam’s current semi-major axis and rotation period and Dinkinesh’s current rotation period are reproduced starting from spin-up fission event initial conditions. The method presented includes the secular effects of YORP, BYORP, and tidal interactions and allows the relative strengths of these effects to be constrained. Improved equations that describe the tidal-BYORP equilibrium in binary asteroid systems will be presented. These equations are (1) a tidal-BYORP equilibrium equation that scales appropriately with secondary mass and (2) an equation for YORP-driven primary spin stability while the secondary is at equilibrium.
Date: Wednesday 06-Mar-2024
Speaker: James R. Beattie (Princeton University, University of Toronto)
Title: Unravelling the workings of the compressible turbulent dynamo
Abstract: Magnetic dynamos are a ubiquitous way of growing, maintaining and structuring magnetic fields across many scales in the Universe. Turbulent, or small-scale dynamos, which power the turbulent components of the magnetic field, provide the reservoir of magnetic energy for large-scale dynamos, which, for example, build coherent fields in accretion discs, via the electromotive force, and hence are an important component of the dynamo ecosystem. Turbulent dynamos have been largely studied both theoretically and numerically in the incompressible regime, which has only limited application in both the interstellar medium and accretion discs, where there can be strong gas density fluctuations and velocity divergence. In this talk I will highlight some of our latest results in compressible (and supersonic) turbulent dynamo calculations and theory, highlighting both the similarities and differences that the supersonic turbulent dynamo has with the incompressible dynamo. Time permitting, I will also talk about our latest calculations on the compressible Kelvin Helmholtz instability dynamo, with applications for growing magnetic fields in binary neutron star mergers.
Date: Wednesday 13-Mar-2024
Speaker: Kyle Parfrey (Princeton Plasma Physics Laboratory)
Title: Relativistic Jets from Accreting Pulsars
Abstract: Though less celebrated than their famous black-hole cousins, most classes of accreting neutron stars also produce jet-like radio emission. This may be due to the interaction of the neutron star's magnetic field with the accretion flow, with the star's rotation the ultimate energy source. I'll describe 3D general-relativistic MHD simulations of magnetized, rotating neutron stars interacting with accretion flows, which demonstrate that the ability of the star-disk interaction to open the star's magnetosphere and drive a jet depends on both the truncation radius of the magnetosphere and the relative orientation of the magnetic fields in the magnetosphere and disk. Introducing obliquity between the star's spin and magnetic axes — essential to model pulsing sources — results in lower jet-launching efficiency but also less sensitivity to the star-disk magnetic orientation. Flux opening can be associated with large eruptions of stellar magnetic flux into the disk, reminiscent of magnetically arrested black-hole systems but with some distinctive features due to the different "boundary conditions" on the central object.
Date: Wednesday 27-Mar-2024
Speaker: Jiaru Li (Northwestern University)
Title: Eccentric Protoplanetary Disks: Theory and Applications
Abstract: High-resolution images taken by ALMA have shown that protoplanetary disks commonly have substructures. The origin of these substructures is one of the most important questions in the planet formation theory. I will discuss the theory related to the eccentricity of protoplanetary disks, which is a m=1 azimuthal substructure. The first part of my talk will introduce the eccentric mode instability (EMI), which is a hydrodynamical process that allows a massive disk to naturally become eccentric due to its self-gravity and the non-adiabatic effects associated with gas cooling. Then, the second part of my talk will focus on two "applications" of disk eccentricity to the formation and dynamical evolution of exoplanets: (1) I will show that eccentric mode instability can lead to the formation of multiple gaps and rings in protoplanetary disks; (2) I will present a new mechanism for generating large planet orbital eccentricity via the resonance sweeping induced by a dispersing eccentric disk.
Date: Wednesday 03-Apr-2024
Speaker: Dongwook Lee (University of California Santa Cruz)
Title: Enhancing numerical algorithms and their applications for predictive astro-fluid dynamics simulations
Abstract: We introduce a groundbreaking advancement in computational fluid dynamics: the GP-MOOD method, a cutting-edge shock-capturing high-order algorithm. This innovative approach leverages Gaussian Processes (GP) to simulate compressible, shock-dominant fluid flows. Specifically, it incorporates the Multidimensional Optimal Order Detection (MOOD) strategy to effectively manage solutions at shocks and discontinuities. MOOD not only enhances numerical stability but also ensures precision through an adaptive shock-capturing framework. Expanding on this foundation, we delve into our pioneering integration of machine learning within the GP-MOOD framework. By employing a neural network (NN) to discern shock patterns, our NN-GP-MOOD approach achieves an unparalleled equilibrium between high-order accuracy and stability, dynamically adjusting to local flow conditions. This sophisticated strategy optimizes numerical accuracy and stability while maintaining the overall predictive capabilities in simulating shock-dominant flows.
Date: Wednesday 17-Apr-2024
Speaker: Sophie Koudmani (University of Cambridge)
Title: Modelling the supermassive black hole-galaxy connection in the multi-messenger era
Abstract: Supermassive black holes (SMBHs) reside at the centres of most massive, if not all, galaxies influencing their host galaxy’s evolution through a complex feedback cycle. Black hole feeding and feedback spans a vast range of spatial scales, from the accretion disc to the cosmic web, so that all past cosmological simulations have had to rely on simple ‘subgrid’ models for SMBH accretion and feedback, significantly limiting their predictive capabilities. Recent observational breakthroughs have challenged these models as the James Webb Space Telescope (JWST) has detected significantly more active SMBHs in the early Universe than had been predicted. The recently detected gravitational wave background from SMBH mergers also points to the need for more efficient early SMBH growth. I will delve into the latest theoretical advancements on modelling active galactic nuclei (AGN) feedback from SMBHs in galaxy formation simulations, presenting a novel unified accretion disc model for SMBHs. This model is based on results from the analytical advection-dominated inflow-outflow solution (ADIOS) and state-of-the-art GR(R)MHD simulations. Utilizing the moving mesh code AREPO, we have performed simulations of single and binary SMBHs within gaseous discs to validate our new model and assess its impact. We find that the disc state significantly affects observable luminosities, and we predict markedly different electromagnetic counterparts in SMBH binaries. Crucially, the assumed disc model shapes SMBH spin magnitudes and orientations, parameters that gravitational wave observatories like LISA and IPTA are poised to constrain. Finally, I will discuss implications for cosmological simulations and share some preliminary results on high-redshift AGN parameter explorations in cosmological boxes to explain the origin of the powerful overmassive SMBHs uncovered by JWST.
Date: Wednesday 24-Apr-2024
Speaker: Ligia Fonseca Coelho (Cornell University)
Title: Purple is the new Green: The Colors of Life as a Tool to Search for Life in the Cosmos
Abstract: Biopigments, crucial components of organisms across the tree of life, significantly influence Earth's landscapes. They protect against radiation, temperature variations, resource scarcity, and general conditions also found on other planets. These pigments also act as distinctive markers of life, displaying unique spectral features linked to specific environmental conditions. In the search for life beyond Earth, biopigments emerge as promising targets for direct biosignature detection. Current surface models primarily focus on chlorophyll-covered planets (green landscapes), neglecting the diversity of other colors on Earth and potential variations on exoplanets around different stars. To address this limitation, we developed a novel spectral catalog encompassing the colors of life associated with various environments, from irradiated to frigid conditions, across different solar systems. This comprehensive spectrum library, spanning the visible to near-infrared range, serves as a valuable resource for researchers and observers. It facilitates the training of retrieval algorithms, optimization of search strategies, and refinement of models for Earth-like planets, aiding future telescopes such as ELTs and HWO. In this research, we see the emergence of new colors indicative of life on planets with unique and varied environmental characteristics, where orange, yellow, or even purple could be the new green.
Date: Wednesday 8-May-2024
Speaker: Beverly Lowell (Northwestern University)
Title: Black hole spin-down by strongly magnetized, jetted disks.
Abstract: One in 10 active galaxies produces relativistic collimated outflows, or jets. Whereas the jets are thought to be powered by black hole spin, how the spin evolves as black holes accrete and produce the jets is poorly understood. Because the spin controls radiative and mechanical black hole feedback on the surroundings, understanding black hole spin evolution history is of paramount importance. The problem becomes particularly urgent given the new LIGO-Virgo-KAGRA constraints on the spin. Without jets, standard (weakly magnetized) luminous disks spin up their black holes to near-maximum dimensionless spin, a = 0.998. However, given sufficient large-scale vertical magnetic flux, it accumulates in the inner disk, obstructs gas infall and leads to a magnetically arrested disk (MAD) state. For a given accretion rate, MADs achieve the maximum jet power and most rapidly extract the rotational energy out of the black hole. I will present 3D general relativistic magnetohydrodynamic (GRMHD) simulations of MADs across a wide range of black hole spin and accretion rate, and model the black hole spin evolution in time. I will do this for both non-radiative and luminous disks, and utilize on-the-fly radiation transport to discern how the results depend on the Eddington ratio. I will show the surprising result that non-radiative MADs spin down their black holes to a very low equilibrium spin, a ≲ 0.1, and develop a semi-analytic model that quantitatively explains the physics behind this dramatic spin-down. I will then explain how luminous MADs also manage to spin down their black holes to a ≈ 0.3, which is still much lower than the standard expectation for luminous disks, a = 0.998. Finally, I will discuss the astrophysical implications of these results and future research directions.
