Upcoming talks

How AGN (Active Galactic Nuclei) feedback operates is one of the unsolved mysteries plaguing modern day astronomy. AGN outflows could explain how this feedback operates and, to investigate this, I use the [O III ] emission line as a tracer of ionised outflows. In this talk, I will present work investigating the link between low-frequency radio emission, using the LOFAR Two-meter Sky Survey Deep Fields at 144 MHz, and [O III ] kinematics, measured from SDSS spectroscopy, for a sample of optically selected AGN . We discover that radio detected AGN are more likely to host an [O III ] outflow compared to radio non-detected AGN . We observe a stronger broad, blue-shifted component in the radio-detected AGN , implying a profound link between low-frequency radio emission and [OIII] outflows. To further link AGN outflows to low-frequency radio emission, we harness the power of widefield VLBI (Very Long Baseline Interferometry) processing and imaging by incorporating the international stations of LOFAR into the data reduction process, to obtain sub-arcsecond radio images. To conclude this talk, I will present the first 0.3” resolution image at 144 MHz of the Boötes Deep Field and early results linking high resolution radio morphologies at 144 MHz to the presence of [O III ] outflows.

Speaker: Emmy Escott (Durham)
Friday 11 April 2025, 11:30-12:30
Venue: Ryle Seminar Room, KICC + online.
Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

Thu 08 May 14:00: How common are misaligned accretion disks around black holes?

Thu, 03/04/2025 - 14:24

How common are misaligned accretion disks around black holes?

Accretion disks around black holes emit across the electromagnetic spectrum, providing a window into strong-field gravity and extreme plasma environments. By analyzing their light curves and spectra, astrophysicists aim to probe fundamental questions about relativistic dynamics and high-energy astrophysics. Traditionally, models of black hole accretion have assumed that the disk’s angular momentum is aligned with the black hole’s spin axis. However, both observations and theoretical considerations increasingly suggest that misalignment—or tilt—is common. In this talk, I will present new insights from cutting-edge radiative general relativistic magnetohydrodynamic (GRMHD) simulations of tilted accretion disks. These simulations reveal that radiative cooling can induce a dramatic nonlinear response: disk warping leads to tearing, breaking the flow into discrete, misaligned sub-disks. The resulting dynamics naturally drive disk precession, which may underlie the quasi-periodic oscillations frequently observed in X-ray binaries and active galactic nuclei. In the second part of the talk, I will question the prevailing view that accretion is primarily driven by magnetorotational instability (MRI)-induced turbulence. I will show that in tilted, warped disks, accretion can instead be mediated by large-scale hydrodynamic shocks—specifically, nozzle shocks—offering a possible explanation for rapid luminosity variability in certain active galactic nuclei.

Speaker: Matthew Liska (Georgia Tech)
Thursday 08 May 2025, 14:00-15:00
Venue: MR14 DAMTP and online.
Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

Add to your calendar or Include in your list

Thu 10 Apr 11:30: Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows KICC Special Seminar

Mon, 31/03/2025 - 14:10

Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows

Broad absorption line (BAL) quasars provide striking evidence of energetic winds driven by accreting supermassive black holes. These outflows are thought to play a crucial role in regulating black hole growth and the host star formation rate, as well as shaping the evolution of galaxies; however, their physical properties—such as radius and energetics—remain poorly constrained. Our group has developed SimBAL, a spectral synthesis tool that enables detailed, physically motivated modeling of BAL quasar spectra. It has allowed us to perform a detailed spectral analysis of a large sample of BAL quasars for the first time and to characterize multi-phase outflows in a quasar discovered at the Epoch of Reionization. I will demonstrate SimBAL’s unique strengths by discussing the results from several projects and how our group has taken a systematic approach to investigate the physics of black hole winds. Lastly, I will introduce the 4MOST–Gaia Purely Astrometric Quasar Survey, an upcoming spectroscopic survey uniquely designed to deliver the first large-scale, color-independent quasar reference sample.

KICC Special Seminar

Speaker: Hyunseop (Joseph) Choi (Université de Montréal)
Thursday 10 April 2025, 11:30-12:00
Venue: Ryle Meeting Room, KICC.
Series: Kavli Institute for Cosmology Seminars; organiser: Steven Brereton.

Add to your calendar or Include in your list

Thu 10 Apr 11:30: Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows KICC Special Seminar

Mon, 31/03/2025 - 08:53

Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows

Broad absorption line (BAL) quasars provide striking evidence of energetic winds driven by accreting supermassive black holes. These outflows are thought to play a crucial role in regulating black hole growth and the host star formation rate, as well as shaping the evolution of galaxies; however, their physical properties—such as radius and energetics—remain poorly constrained. Our group has developed SimBAL, a spectral synthesis tool that enables detailed, physically motivated modeling of BAL quasar spectra. It has allowed us to perform a detailed spectral analysis of a large sample of BAL quasars for the first time and to characterize multi-phase outflows in a quasar discovered at the Epoch of Reionization. I will demonstrate SimBAL’s unique strengths by discussing the results from several projects and how our group has taken a systematic approach to investigate the physics of black hole winds. Lastly, I will introduce the 4MOST–Gaia Purely Astrometric Quasar Survey, an upcoming spectroscopic survey uniquely designed to deliver the first large-scale, color-independent quasar reference sample.

KICC Special Seminar

Speaker: Hyunseop Choi (Université de Montréal)
Thursday 10 April 2025, 11:30-12:00
Venue: Ryle Meeting Room, KICC.
Series: Kavli Institute for Cosmology Seminars; organiser: Steven Brereton.

Add to your calendar or Include in your list

Fri 04 Apr 11:30: The first stars: window to cosmic dawn

Fri, 28/03/2025 - 18:09

The first stars: window to cosmic dawn

The era of cosmic dawn began with the first stars that formed in the Universe a mere 200 – 300 million years after the Big Bang. These stars produced the first supernovae and black holes, enriched the interstellar medium (ISM) with metals, were the building blocks of the first galaxies, and significantly contributed to cosmic reionization. However, compared to star formation and feedback in metal-rich environments today, the lack of direct observations at low metallicities as well as high redshifts has posed a significant challenge for understanding the physics behind their formation and evolution. In this talk, I will introduce POPSICLE , a new framework for high resolution simulations that caters to star formation and feedback in low metallicity ISM reminiscent of redshift > 10 galaxies. I will describe how incorporating the full spectrum of ISM physics coupled to stellar evolution is crucial to constrain the stellar initial mass function (IMF) and feedback in such environments. I will particularly focus on Population III stars, and discuss their potential as seed black holes in the early Universe. I will conclude by showcasing the capability of GPU -accelerated simulations to revolutionize our understanding of the astrophysics of cosmic dawn, and to bring theory at par with state of the art observations from JWST .