Upcoming Talks

Wed 24 Jan 13:15: The black hole mass-metallicity relation and insights into galaxy quenching

Mon, 22/01/2024 - 11:12

The black hole mass-metallicity relation and insights into galaxy quenching

Understanding the quenching of star formation in galaxies remains a central question within extragalactic astrophysics. In this talk I will explore the intricate interplay between galaxy quenching, black hole mass, and ‘starvation’. Previous research has established a strong correlation between quiescence and black hole mass, while other studies have highlighted the role of ‘starvation’—the halting of gas inflows—as a driving force in quenching, based on rapid gas depletion through star formation and chemical enrichment. This investigation bridges the gap between these findings, shedding light on the underlying mechanisms. Leveraging an extensive dataset of galaxies, this study uses random forest regression and partial correlation coefficients to uncover the fundamental relationships governing stellar metallicity with respect to other galaxy characteristics. I will show that for actively star-forming galaxies, stellar metallicity exhibits a strong dependence on stellar mass. However, intriguingly, for passive galaxies, a dramatically different narrative emerges, where the primary driver of stellar metallicity is the black hole mass. This means the integrated impact of black hole feedback emerges as the crucial determinant, cutting off gas inflows and inducing a state of ‘starvation’, ultimately leading to the observed rapid rise in stellar metallicity. This, in turn, paves the way for the transition of a galaxy from star-forming to quiescent. This finding not only deepens our understanding of galaxy evolution but also offers key insights into the intricate mechanisms shaping the fate of galaxies across cosmic epochs.

Speaker: William Baker
Wednesday 24 January 2024, 13:15-14:05
Venue: The Hoyle Lecture Theatre + Zoom .
Series: Institute of Astronomy Seminars; organiser: .

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Wed 24 Jan 14:00: On-shell techniques for the standard-model EFTs

Fri, 19/01/2024 - 10:07

On-shell techniques for the standard-model EFTs

Bypassing fields, operators and Lagrangians to target directly physical amplitudes advantageously avoids gauge and field-redefinition redundancies. Unitarity and analyticity allow for the construction of on-shell amplitudes, recursively in leg and loop numbers. After decades of developments focusing mostly on renormalisable theories, the associated on-shell amplitude techniques have recently been more extensively applied to effective field theories, including those which parameterise hypothetical heavy physics appearing beyond the standard model. The enumeration of independent operators can be substituted for that of contact-term amplitudes. In a given scattering, the possible kinematic structures can be fully characterised. Unitarity and analyticity allow for the derivation of positivity constraints, for the extraction of anomalous dimensions and of matching coefficients. This talk will cover some of these developments.

Speaker: Gauthier Durieux (Universite Catholique de Louvain)
Wednesday 24 January 2024, 14:00-15:00
Venue: MR2.
Series: Theoretical Physics Colloquium; organiser: Hannah Banks.

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Fri 02 Feb 11:30: IoA/KICC Open Day

Thu, 18/01/2024 - 21:49

IoA/KICC Open Day

Abstract not available

Speaker: Matthew Bothwell & Hannah Strathern
Friday 02 February 2024, 11:30-12:30
Venue: Ryle seminar room + online.
Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Tue 30 Jan 14:00: Transition region spectroscopy with the Hinode/EIS instrument

Wed, 17/01/2024 - 17:08

Transition region spectroscopy with the Hinode/EIS instrument

The EUV Imaging Spectrometer observes the Sun in the 170-292 Angstrom wavelength range, which is dominated by coronal emission lines that are mainly due to iron ions. Valuable science can still be obtained from transition region ions formed in the 0.1-0.8 MK temperature range, and some recent results are presented here.

Mg VII and Si VII (formed at 0.6 MK) produce a number of lines that are widely used for diagnostics of coronal loops. However, the standard reference wavelengths for the ions’ lines are clearly discrepant with the wavelengths measured from EIS , leading to erroneous Doppler velocity measurements. I demonstrate how EIS (which does not have an absolute wavelength calibration) can be used to obtain new reference wavelengths for the lines in combination with Astrophysical infrared measurements. The new wavelengths for Mg VII and Si VII will be added to the CHIANTI database. In addition, the EIS data show that the two ions are formed at almost exactly the same temperature and the Mg/Si relative abundance is enhanced over photospheric values by about 50%.

The coolest ion observed by EIS (other than He II) is O IV , formed at 0.1 MK. It has a rich spectrum in the EIS wavelength range with more than 20 emission lines, however most of the lines are so weak they cannot be measured in normal solar conditions. A flare spectrum from 9 March 2012 is presented where the lines can be measured, and new diagnostics are presented that yield an O IV temperature of log(T/K)=5.10 and a density of log(Ne/cm^-3)=12.55 for the flare ribbon. The results are interpreted in terms of ionization and flare models.

Speaker: Peter Young (NASA Goddard and Northumbria university)
Tuesday 30 January 2024, 14:00-15:00
Venue: MR5 DAMTP and online - ** CHANGED TIME AND LOCATION.
Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

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Mon 05 Feb 14:00: Dynamo action, magnetorotational instability, Alfvén waves: Theory and experiments on astrophysical magnetohydrodynamics

Wed, 17/01/2024 - 11:35

Dynamo action, magnetorotational instability, Alfvén waves: Theory and experiments on astrophysical magnetohydrodynamics

Abstract not available

Speaker: Frank Stefani (Helmholtz-Zentrum Dresden)
Monday 05 February 2024, 14:00-15:00
Venue: MR14 DAMTP and online.
Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

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Mon 10 Jun 13:00: Title to be confirmed

Wed, 17/01/2024 - 10:59

Title to be confirmed

Abstract not available

Speaker: Vincent Vennin (ENS, Paris)
Monday 10 June 2024, 13:00-14:00
Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
Series: Cosmology Lunch; organiser: Dr Dong-Gang Wang.

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Mon 12 Feb 13:00: How much (robust) cosmological information can we obtain from galaxy clustering?

Tue, 16/01/2024 - 18:52

How much (robust) cosmological information can we obtain from galaxy clustering?

All large-scale structure cosmologists are faced with the question: how do we robustly extract cosmological information, such as on dark energy, gravity, and inflation, from observed tracers such as galaxies whose astrophysics is extremely complex and incompletely understood? I will describe why guaranteeing this robustness is so difficult, and how a perturbative effective-field-theory (EFT) approach offers such a guarantee when focusing on galaxy clustering on large scales. The natural next question then is: how much cosmological information is left on these large scales if we marginalize over all the free parameters introduced in the EFT ? To answer this question, I will introduce our implementation of the EFT on a lattice as an explicit field-level forward model, which can be used both for full Bayesian inference at the field level and for likelihood-free (simulation-based) inference using summary statistics. Finally, I will show first results comparing full field-level inference and summary statistics on fully nonlinear mock tracers.