External Seminars

The following talks take place at DAMTP, the Cavendish Laboratory or the Institute of Astronomy and are not organised by this group. However, they might by related to research that is done within this group at DAMTP.

CMB Lensing: Fundamental Physics from Maps of the Invisible

Dark matter not only forms an invisible cosmic scaffolding within which galaxies form, its distribution in the universe also contains a wealth of information about neutrinos, dark energy, and physics at the earliest times. Measurements of gravitational lensing in the cosmic microwave background (CMB) allow this matter distribution to be directly seen and mapped.  In my talk, I will first discuss recent measurements of CMB lensing and their scientific implications. I will then explain why upcoming measurements of the CMB lensing signal, with experiments such as AdvancedACT and Simons Observatory, will be remarkably powerful probes of cosmology. Lensing is not only a signal, however, but also a source of noise that limits how much we can learn about the very early universe. With illustrations from recent work, I will explain why delensing Рremoving the lensing effect to reveal the primordial sky Рis crucial for the future of CMB cosmology.

Evolution of the UV luminosity function of AGN out to redshift 7

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iPhones and Dysons: using fluid dynamics to tailor technology

As technology continues to advance, new strategies that involve a range of scientific disciplines are required. Mathematicians can provide frameworks to predict operating regimes and manufacture techniques. In this talk we present two case studies: the fabrication of precision glass, for smartphones and new flexible devices; and the development of superior filters for vacuum cleaners. In each case we use asymptotic analysis to determine the fabrication protocol required to produce a desired final product.

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Weather on Brown Dwarfs: New Insights from Synoptic Spectrophotometry and Fluid Instability Models

The coolest stars and brown dwarfs exhibit chemical, spectral and variability signatures indicating the presence of photospheric condensate clouds, which in turn serve as tracers for rotational and atmospheric dynamics. However, the precise nature of these clouds – their vertical, azimuthal and temporal structure, and their composition – have remained a challenge to model and infer. In this talk, I provide a brief summary of the research to date on brown dwarf weather, then focus on two areas in which important insights have emerged. First, I show that synoptic spectrophotometry, now possible at high precision with ground-based telescopes, demonstrates that small-grain particles at high altitudes may be the primary drivers for observed variability. Second, new atmosphere models integrating fluid instabilities are now able to reproduce many spectral signatures attributed to clouds without the need for cloud opacity. I attempt to synthesize these seemingly contrary perspectives and propose ways to further test what roles clouds do or do not play in shaping the spectra of cool brown dwarfs and hot exoplanets.

IR Spectroscopic Tracers for Galaxy Evolution Studies: the Spitzer/Herschel database

The rest-frame mid- to far-IR range contains a unique suite of spectral lines and dust features that allow us to determine the physical conditions in galaxies (e.g. density, ionisation, heavy element abundances) using tracers with a feeble response to both extinction and temperature.

In this study we present a spectroscopic database of mid- to far-IR fine-structure lines observed with Spitzer/IRS and Herschel/PACS for a sample of 170 local AGN , 20 starburst galaxies, and 43 dwarf galaxies. The observations are compared to a set of Cloudy photoionisation models to estimate the physical quantities through the different diagnostic diagrams. The new [OIV]25.9um/[OIII]88um vs [NeIII]15.6um/[NeII]12.8um diagram is proposed as new IR BPT diagnostic diagram, able to separate: 1) AGN activity from any kind of star formation; and 2) low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed [OIV]25.9um/[OIII]88um ratios, which are much higher when compared to the predicted values. Finally, the ([NeIII]15.6um 12.8um)/([SIV]10.5um [SIII]18.7um) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity.

Swimming in a turbulent world

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Stop. Think. Click.

A presentation from the Head of Computer Emergency Response Team, at the University of Cambridge. Case Studies of recent information security incidents in the University of Cambridge, and how to mitigate the threat.

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Sackler Lecture 2017

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