UCL Astrophysics Group


Past Seminars

Seminars 2022/2023

Term 1

26-Sept-2022: Joss Bland-Hawthorn (Sydney), The corrugated disc in the Milky Way

There has been evidence for wave-like patterns across the Milky Way disc for more than 50 years, mostly observed in cool gas and star forming regions along spiral arms. In 2018, the ESA Gaia satellite revealed similar corrugations for the first time in the stellar disc. But are these patternseven related? What excites them and what can we learn? We will attempt to provide answers based on new observations and simulations. Looking forward, a wide range of experiments based on bending and breathing modes will become possible with the new generation of Galactic experiments.

03-Oct-2022: Will Dunn (UCL), A Seminar in 2 Parts: 1. Using X-ray Observatories to Study High Energy Astrophysics at Planets; 2. Orbyts – Our Multi-Award-Winning Research-with-Schools Programme 

Part 1I’ll introduce X-ray emissions from the outer planets mainly focusing on Jupiter but including a brief review of last year’s discovery that Uranus generates X-ray emissions. The Jovian system is a treasure trove of X-ray sources: diverse and dynamic atmospheric and auroral emissions, diffuse radiation belt and Io torus emissions, and plasma-surface interactions with Jupiter's moons. The system is a rich natural laboratory for astronomical X-rays with each region showcasing its own X-ray production processes: scattering and fluorescence of solar corona emissions; charge exchange emissions from energetic ions; Inverse-Compton, thermal and non-thermal bremsstrahlung emissions from relativistic electrons; and fingerprint fluorescence lines indicative of elemental composition and the potential for life on the Galilean satellites. For the high energy astrophysics domain, perhaps Jupiter's greatest attribute is the opportunity to connect observed X-ray emissions with in-situ plasma and magnetic field measurements of the precise physical processes that lead to them - irreplaceable ground truths for systems that cannot be visited in-situ. Such simultaneous studies have revealed that Jupiter's spectacular soft X-ray flares and pulsations are produced by wave-particle interactions, while the bremsstrahlung aurorae vary with magnetodisk reconnection and dipolarisation. While many remote signatures remain to be linked with their source processes, the future is bright, with synergistic Chandra, NuSTAR, XMM-Newton and Juno in-situ measurements continuing to provide revolutionary insights in the coming years, while JUICE and Europa missions with Athena will enable a new legacy. However, to truly characterise some emissions (e.g. mapping Galilean satellite elemental composition) in-situ X-ray instrumentation is a necessity. Recent advances enable compact, lightweight, X-ray instrumentation perfectly suited for Jupiter science. I’ll close the first half of the talk by reviewing a feasible, low-risk concept that we submitted to the NASA Heliophysics decadal this month, COMPASS, which would paradigm-shift our understanding of the system and provide a stepping stone from planetary science to astrophysics.Part 2“Orbyts has surpassed anything I could have imagined - not only have our students been consistently blown away by the science of other planets, it has helped them better understand the value of their own one. Orbyts is definitely one of the coolest things I've been exposed to in my 15 year career.”“It’s clear to me that the Orbyts project has been the most successful project we have been fortunate to work with and its importance cannot be overstated.”So what is Orbyts, how is it having such a profound impact and what makes teachers think it’s so cool?Orbyts is a movement organised by our colleagues in P & A that creates partnerships between scientists and schools. This provides school students with relatable science role models while empowering them to conduct original research projects. This structure of regular interventions, inspirational role models and active ownership of research is proving to be transformative; dispelling harmful stereotypes and profoundly shifting perceptions of science and scientists. It is particularly impactful for groups historically excluded from science. For example, our partner schools report 100% increases in girls uptake of A-level physics, following participation in an Orbyts project at GCSE.Last year, our fantastic planetary researchers partnered with school students to support research-with-schools projects on: exoplanets, star formation, galaxies, aurorae, AI and machine learning, plasma physics, comets, space weather and AGN.  I’ll showcase a whistle-stop tour through some of these projects, where possible letting recorded presentations by the schools do the talking.I’ll overview the process of creating projects, the general structure and timeline of them and what our evaluation data shows about the value of different aspects of the programme on students, teachers and researchers. I’ll also speak briefly on the best practice seminars/workshops on inclusivity, teaching, communication and management training that we offer for interested researchers and on how we pay PhD students for their time producing and delivering projects.  We are constantly seeking to improve the programme and to collaborate and partner with new people to improve the scienceexperiences of everyone involved – we hugely welcome any contact about Orbyts.

10-Oct-2022: Noam Soker (Technion, Israel), The role of jets in exploding supernovae and in shaping their remnants

I will present new results on the role of jets in exploding core collapse supernovae and in shaping their ejecta. I will discuss the role of jets in powering peculiar supernovae in particular superluminous supernovae and other energetic transients. The imprints of jets in supernova remnants have many similarities with morphologies of planetary nebulae that are known to be shaped by jets, teaching us on the importance of jets in the final phases of stellar evolution.

17-Oct-2022: Cesar Bertucci (Buenos Aires), Extreme space weather at Saturn and Titan as seen from the Cassini spacecraft

Titan is Saturn’s largest moon and the only in the Solar System to possess a dense atmosphere. Unlike its parent planet, Titan does not possess a significant intrinsic magnetic field and therefore the moon’s atmosphere is directly exposed to the plasma environment. As a result of the exchange of energy and momentum between Titan’s atmosphere and the ambient plasma, an ‘induced magnetosphere’ will form around the moon. But most important, Titan’s atmospheric plasma will be accelerated and escape into space.  With an orbital radius of nearly 20 Saturnian radii, Titan usually sits inside Saturn’s rotating magnetosphere. However, during periods of high solar wind pressure, Titan can be exceptionally found outside Saturn’s magnetopause and bow shock.  In this seminar we present observations by the Cassini spacecraft (in orbit around Saturn between 2004 and 2017) that illustrate how the Titan Saturn magnetospheric system reacts to the impact by a series of interplanetary coronal mass ejections (ICME) around December 2013. This is new evidence that provides relevant context information to Cassini’s unique observations of Titan in the supersonic solar wind during the spacecraft’s 96th flyby (Bertucci et al., 2015) and a new look to the way solar energetic events such as ICMEs behave in the outer solar system.

24-Oct-2022: Ed Gillen (QMUL), Probing the early evolution of stellar and planetary systems

Stars and planets both evolve dramatically during their first several hundred million years, which has important implications for the subsequent diversity and habitability of planetary systems. Young stellar associations, open clusters and co-moving groups are fruitful astrophysical laboratories because their members share broad coevality, composition and location. Combining information from groups at different ages offers a powerful tool to understand the early evolution of stellar and planetary systems. Recent photometric surveys have provided key advances in this area, first with the Kepler/K2 mission and now with the Transiting Exoplanet Survey Satellite (TESS) and the Next-Generation Transit Survey (NGTS). I will discuss various avenues to probe the early evolution of stars and planets, beginning with recent successful searches for young transiting planets, which also led to serendipitous discoveries of young transiting brown dwarfs and eclipsing binaries. I will then present recent work on the early evolution of stellar rotation before concluding with a brief look at how early stellar flare activity might influence subsequent planet habitability. 

31-Oct-2022: James Kirk (Imperial), Understanding the population of exoplanets via observations of their atmospheres

The exoplanet population is incredibly diverse and in stark contrast to the planets in our solar system. My research focusses on improving our understanding of this diversity via observations of transiting exoplanet atmospheres. In this talk, I will present the first results from JWST’s Early Release Science programme that is using all four instruments to obtain a comprehensive and exquisite spectrum of the highly inflated Saturn-mass exoplanet WASP-39b. I will compare the results we are getting from JWST with my previous studies of this planet using data from Hubble, Spitzer and my LRG-BEASTS programme. LRG-BEASTS, or the Low Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy, is measuring the optical spectra of 29 transiting exoplanets to determine how exoplanet spectra vary with temperature (750 to 2500K) and mass (0.1 to 3.2 Jupiter masses). Finally, I will present results from my Keck programmes that are measuring the atmospheric loss of exoplanets via high spectral resolution observations of neutral helium at 1.08 microns. I will place my results into the emerging field of helium transmission spectroscopy and discuss how helium can advance our understanding of atmospheric loss and its role in shaping the exoplanet population.

07-Nov-2022: Anthony Brown (Leiden), The Gaia mission, Gaia DR3, and science highlights from the Gaia data releases

The European Space Agency's Gaia space mission, launched in 2013, is designed to measure the brightnesses, colors, positions, distances, and motions (in three dimensions) of almost two billion of the Milky Way's hundred billion stars. These measurements are yielding new insights about the internal structure and formation history of the Milky Way, thanks in part to a series of increasingly comprehensive data releases that any member of the astronomical community can access. In this talk, I will introduce the Gaia mission and summarize the latest data release, Gaia DR3. This discussion will be complemented by highlights of the science results from the Gaia data releases, showcasing among others the impact of Gaia on solar system studies, the Milky Way's accretion and recent dynamical histories, and understanding matter in extreme states.

21-Nov-2022: Ignacio Ferreras (IAC, Tenerife), The information content of galaxy spectra

Most of the observable space in astrophysics comes as photons. Spectra therefore represent an optimal source of information, as the flux is being classified with respect to wavelength. In extragalactic astrophysics, the most “visible” component, i.e. stars, output most of their radiant energy in the rest-frame NUV-optical-NIR window, and mainly consist of a superposition of absorption lines overlaid on a continuum. These photons encode the properties of the photospheres of stars, covering a wide and complex range of mass, age and chemical composition. In this talk I will present an overview of the difficulties underlying the analysis of stellar populations from observable data, and explain, from an information theory approach, the caveats of traditional methods aimed at extracting formation histories from spectra.

28-Nov-2022: Alexandra Amon (Cambridge), Cosmology from weak lensing: The S8 tension

Weak lensing surveys have consistently reported low values of the clustering amplitude (S_8) compared to that predicted by Planck primary Cosmic Microwave Background. I present the constraints from the Dark Energy Survey (DES) Year 3 cosmic shear analysis from >100 million galaxies spanning >4000 square degrees, constituting the most powerful weak lensing dataset to date.  I’ll emphasise the robustness to the main systematics that weak lensing analyses are susceptible to, such as the redshift and shear calibration, as well as the modelling of astrophysical effects. Finally, I will present a potential solution to the S8 tension and the avenues underway to understand our observations.

05-Dec-2022: Jim Dunlop (Edinburgh), Galaxies in the young Universe

I will discuss recent breakthroughs in our understanding of galaxy evolution in the first billion years, including the impact of early galaxy growth on the (hydrogen) reionisation of the IGM. I will focus primarily on recent observational breakthroughs, especially with ALMA, JCMT, VISTA, Subaru, HST and now (in particular) with the James Webb Space Telescope (JWST), but will also briefly consider the connections and tensions with theoretical predictions. I will endeavour to provide a balanced overview of this rapidly moving field, while highlighting recent advances that have been led from Edinburgh. Finally, I will consider the prospects for further improvement in our knowledge of early galaxy formation over the coming years.

Term 2

9-Jan-2023: Anke Arentsen (Cambridge), Galactic Archaeology with the oldest stars in the Milky Way

The oldest, most metal-poor stars we find in the Milky Way today were born in pristine environments in the early Universe. They contain unique clues about the First Stars and the early formation and evolution of our Galaxy. Most metal-poor stars are found in the Galactic halo, but the central halo overlapping with the Galactic bulge has often been avoided — it is challenging to identify metal-poor stars in this dusty, crowded area of the sky. In this talk, I will introduce the Pristine Inner Galaxy Survey (PIGS) which has reached unprecedented efficiency in finding very metal-poor stars in the Galactic bulge region. I will present recent PIGS results on the chemistry and the kinematics of the metal-poor inner Galaxy, and discuss what they can teach us about this ancient component of the Milky Way.

23-Jan-2023: Ana Lopez-Sepulcre (Grenoble), Organic molecules in protostars: lessons learnt from spectral observations

The gas associated with the early stages of star formation contains traces of a large variety of molecular species, many of which are organic in nature. Interestingly, we observe a substantial chemical diversity among protostars, with some objects being enriched in what astrochemists label interstellar complex organic molecules (iCOMs), such as methyl formate (HCOOCH3) and formamide (NH2CHO), while others are overabundant in unsaturated carbon chains such as C4H. What is the cause of this diversity? And where should we place the proto-solar-system in this chemical context: was it rich in iCOMs, or in carbon chains, or in both? Thanks to the development of sensitive broadband (sub-)millimetre instrumentation, both in single-dish telescopes and interferometers, we are currently witnessing big steps forward in this area. At the same time, new observational and theoretical challenges are arising which make us look to the future with hopeful eyes. I will summarise what we have learnt, in the past decade or so, about the molecular contents in solar-mass protostellar sources, and suggest a few guidelines to stimulate progress in the field.

30-Jan-2023: Ziri Younsi (MSSL, UCL), Studying Black Holes on Event Horizon Scales

Black holes possess gravitational fields so intense that nothing, not even light, can escape their event horizons, rendering them "invisible". For over a century, black holes were conjectured to exist, yet direct observational confirmation of their existence remained elusive. However, in 2019 the Event Horizon Telescope (EHT) Collaboration (EHTC) published the first ever "image" of a supermassive black hole. In 2022 the EHTC subsequently published the first image of the Milky Way supermassive black hole. In this talk I will present an overview of the physics of black holes and radiation processes on event horizon-scales, together with an introduction to the EHT array and the wider EHTC. I will discuss how these and other complimentary observations can provide important new insights into both the fundamental properties of black holes and the physical processes occurring in their surrounding environments. Finally, I will discuss some of the exciting future prospects for horizon-scale studies of black holes.

6-Feb-2023: Mehrnoosh Tahani (Stanford), Novel views of three-dimensional interstellar magnetic fields

Recent observations, particularly those obtained by the Gaia mission, have greatly enhanced our understanding of the three-dimensional (3D) structure and evolution of the interstellar medium (ISM). The ISM evolution cannot be fully understood without observing interstellar magnetic fields. Magnetic fields influence the galaxy evolution and the formation of clouds, stars, and planets. However, their role is poorly understood, mainly due to significant limitations in observing 3D magnetic fields. To map the 3D magnetic fields, I first developed a novel technique, based on Faraday rotation measurements, to detect the line-of-sight component of magnetic fields of star-forming clouds. We examined the technique on four regions of Orion A, Orion B, California and found it to be in good agreement with the limited Zeeman measurements available in the same regions. I then incorporated our line-of-sight and Planck’s plane-of-sky magnetic field observations, along with models and statistical tools, to examine the 3D magnetic field morphology associated with these clouds. Finally, we used Galactic magnetic field models to reconstruct the complete 3D magnetic field morphologies, including their direction (associated with the Orion A and Perseus clouds). These 3D studies provide novel constraints on theories for the formation and evolution of star-forming clouds. In this talk, I will discuss these 3D observing techniques, our results and their connection to larger ISM magnetic fields, and future directions.

13-Feb-2023: Roland Bacon, WST (Lyon) - The Wide Field Spectroscopic Telescope

The WST project aim to study and built an innovative 10-m class wide-field spectroscopic survey telescope (WST) in the southern hemisphere with simultaneous operation of a large field-of-view (5 sq. degree) and high multiplex (20,000) multi-object spectrograph facility with both medium and high resolution modes (MOS), and a giant panoramic integral field spectrograph (IFS). The ambitious WST top-level requirements place it far ahead of existing and planned facilities. In just its first 5 years of operation, the MOS will target 250 million galaxies and 25 million stars at medium resolution + 2 million stars at high resolution, and 4 billion spectra with the IFS.  WST will achieve transformative results in most areas of astrophysics. The combination of MOS and IFS spectroscopic surveys is one of the key aspects of the project. It is very attractive because of the high complementarity between the two approaches. I will detail this innovative point using the example of the MOS and MUSE surveys performed in the CFS region. The project aims to be the next major post-ELT project. It is supported by a large consortium of very experienced institutes plus ESO, representing 9 European countries and Australia.

20-Feb-2023: Nikos Nikolaou (UCL), Machine Learning for Scientific Applications

The use of Machine Learning methods for speeding up scientific discovery is now widespread, opening up new opportunities across scientific domains. But with new opportunities come new challenges in terms of training, evaluating, adopting and -ultimately- drawing scientific insights from ML models. In this talk we will overview some of the key aspects that need to be taken into consideration when applying machine learning models in scientific contexts. We will discuss select topics related to the evaluation of ML algorithms and models, uncertainty estimation, encoding of domain knowledge into the models, model interpretability, causal inference and more. We will relate these to examples from scientific applications, primarily in Exoplanetary Science.

27-Feb-2023: Chiaki Kobayashi (Hertfordshire), The Origin of Elements and Their Evolution in Galaxies

Stars are fossils that retain the history of their host galaxies. Elements heavier than helium are created inside stars and are ejected when they die. Elements heavier than iron (such as gold) are also produced by neutron star mergers. From the spatial distribution of elements in galaxies, it is therefore possible to constrain star formation and chemical enrichment histories of the galaxies. This approach, Galactic Archaeology, has been popularly used for our Milky Way Galaxy with a vast amount of data from Gaia and multi-object spectrographs. This approach can also be applied to external galaxies thanks to integral field units. Theoretical predictions are also available including detailed chemical enrichment into hydrodynamical simulations from cosmological initial conditions. My team has been running chemodynamical simulations of a Milky Way type galaxy as well as a cosmological box, and I will show how the spatial distribution of elements evolved in the Milky Way and in galaxies with different masses, comparing to the latest observations with Gaia and JWST.

13-Mar-2023: Ing-Guey Jiang (NTHU, Taiwan), From Exoplanet Physics to Planet Formation

The field of planet formation has been boosted remarkably by the fast development of exoplanet physics which includes the continuous flow of new exoplanet detections, the observations of exoplanet atmospheres, the orbital modeling of exoplanets, and the study of extra-solar multi-planet architecture. These results will be reviewed and the connections with planet formation will be discussed.

Term 3

15-May-2023: Matthew Colless (Australian National University), Galaxy Structure and Dynamics from Integral Field Spectroscopy Surveys

The SAMI galaxy survey on the Anglo-Australian Telescope (AAT) has provided integral field spectroscopy with sufficient signal-to-noise to allow detailed analysis of the structure and dynamics for a large sample of galaxies spanning a wide range of properties in both field and cluster environments. I will discuss some recent results from SAMI, focussing on two topics: (1) kinematic decompositions of the bulge and disk components of galaxies, and the insights these provide on the processes that shape the morphology and stellar populations of galaxies, and (2) flips in the alignments between galaxy spins and the filaments of the cosmic web, and the light these shed on the processes that contribute to assembling the angular momentum of galaxies. I will conclude with an update on the Hector integral field spectrograph, recently commissioned on the AAT, and the Hector galaxy survey that has just begun and aims to extend the scope of the science addressed with SAMI.

22-May-2023: Or Graur (Portsmouth), Rage Against the Dying of the Light: old supernovae teach us new tricks

Supernovae - the explosions of stars - play a variety of roles in the workings of the Universe. Some of them are also used as tools for other experiments in astrophysics. Type Ia supernovae, specifically, are used to measure distances to faraway galaxies and, in turn, constrain cosmology. However, we still do not know exactly what types of star systems explode as these supernovae or how the explosions take place. In my talk, I will show how Hubble Space Telescope observations of Type Ia supernovae years after their explosion shed new light on the physics of their explosions and progenitors.

12-Jun-2023: Veerle Sterken (ETH Zurich), Cosmic dust in- and outside of the solar system

Interstellar dust from the local interstellar cloud moves through the heliosphere due to the relative motion of the solar system with respect to its immediate interstellar surroundings. Once in the solar system, its properties can be measured in situ by cosmic dust detectors on spacecraft, or they can be captured and brought back to the Earth for further laboratory analysis. Inside the solar system, dust from comets, dust ejected from (atmosphereless) planetary surfaces or dust coming from subsurface oceans (e.g. Enceladus) and from volcanoes (e.g. Io), are carriers of valuable information about the history of the solar system and about the interiors of these moons today. In this talk, we introduce the small but surprisingly rich field of in situ cosmic dust science: the science cases, measurement techniques, calibrations, and simulations. We show how in situ dust science and heliospheric sciences go hand in hand, and we finish with a discussion on current and near-future missions and mission concepts for dust research.

Seminars 2021/2022

Term 1

4-Oct-2021: Kate Pattle (UCL), Magnetic fields and the evolution of star-forming regions

In this talk I will discuss the role played by magnetic fields in the evolution of star-forming filaments in nearby molecular clouds.  I will particularly discuss recent observations made using the James Clerk Maxwell Telescope's (JCMT's) POL-2 polarimeter, including by the JCMT BISTRO (B-Fields in Star-Forming Region Observations) Survey.   I will present observations of several nearby molecular clouds, discussing commonalities between these regions and the search for a characteristic size or density scale at which magnetic fields lose their dynamic importance in the evolution of star-forming regions to gravitational instability.  I will also discuss the first hints that we are getting about the effects of stellar feedback on magnetic fields in dense star-forming gas.

11-Oct-2021: Roberto Trotta (Imperial/SISSA), StratLearn: A general-purpose method for supervised learning under covariate shift with applications to observational cosmology

Supervised machine learning will be central in the analysis of upcoming large-scale sky surveys. However, selection bias for astronomical objects yields labelled training data that are not representative of the unlabelled target data distribution. This affects the predictive performance with unreliable target predictions and poor generalization.

I will present StratLearn, a novel and statistically principled method to improve supervised learning under such covariate shift conditions, based on propensity score stratification. In StratLearn, learners are trained on subgroups ("strata") of the data conditional on the propensity scores, leading to improved covariate balance and much-reduced bias in the model fit.

This general-purpose method has promising applications in observational cosmology, improving upon existing conditional density estimation of galaxy redshift from Sloan Data Sky Survey (SDSS) data; in the classification of Supernovae (SNe) type Ia from photometric data, it obtains the best reported AUC on the "SNe photometric classification challenge". If time allows, I'll discuss the embedding of such a classification into a full analysis of SNe data to estimate cosmological parameters.

18-Oct-2021: John Coxon (Southampton), The distribution of Birkeland currents in time and space

The magnetosphere is the region of space in which physical interactions are dominated by Earth’s magnetic field. The solar wind interacts with the magnetopause, which is the edge of the magnetosphere. Birkeland currents communicates these interactions and impacts between the magnetopause and the rest of the magnetosphere, and these currents flow along Earth’s magnetic field lines. It is these currents that electrodynamically link the magnetopause with the planet’s atmosphere, and this is a key part of the mechanism responsible for space weather impacting us on the Earth’s surface.

I use observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to investigate the Birkeland currents at the Earth’s poles and the timescales of those currents. I will show work demonstrating that the Birkeland currents display different behaviour in the Northern and Southern Hemispheres. Then, I will move onto discussing the morphology of Birkeland currents during substorms and the timescales of currents’ reaction to the magnetic field carried by the solar wind (the Interplanetary Magnetic Field), which allows me to discern the way in which key space weather phenomena affect us on the ground. Finally, I will discuss how AMPERE data are distributed and use this to predict the location and likelihood of extreme current flows affecting Earth.

25-Oct-2021: Sthabile Kolwa (Johannesburg), The link between cold molecular gas depletion and AGN feedback in distant radio galaxies

Radio galaxies are the massive elliptical hosts of radio-loud active galactic nuclei (AGN) which emit powerful radio jets known to impact the dynamical state of halo gas surrounding these galaxies via AGN feedback processes. The circumgalactic medium (CGM) is the region of a galaxy’s halo that connects its interstellar medium (ISM) to the intergalactic medium (IGM). Through the CGM, filamentary gas accretion from the cosmic web can occur in addition to outflows of gas from the galaxy’s ISM. In seeking to further understand the AGN and host galaxy connection, we can place observational constraints on the properties of gas within the extended halos of radio-loud AGN host galaxies where the AGN are considered to have a tremendous impact on the ISM and extended halo gas.

In this talk, I will provide an overview of what we already know about the structure of the multi-phase CGM in high-z radio galaxies and go on to present new results from ALMA+MUSE data which allow us to trace the cold molecular and warm ionised gas components of the CGM, respectively. My talk will focus primarily on the inferred properties of molecular gas traced via neutral carbon emission observed by ALMA in seven radio galaxies at z=2.9–4.1. Combining these results with the known star-formation rates of the galaxies, we approximate their star-forming efficiencies and gas fractions. In doing so, we find that radio-loud AGN hosts tend to have low gas fractions and high star-forming efficiencies relative to normal star-forming galaxies. I will discuss the implications of our findings on the general understanding of AGN feedback may occur in radio galaxies within the early Universe.

1-Nov-2021: Katy Clough (Oxford / QMUL), Black holes as probes of light dark matter environments

With no discovery of WIMPs to date, attention is turning towards lighter mass (sub eV) candidates for dark matter such as axion-like-particles. I will discuss their wave-like behaviour, and how this may manifest in signatures from such light particles in strong gravity environments. In particular, I will discuss the dynamical friction experienced by black holes moving through such matter, which causes a dephasing in the gravitational wave signal of LISA binaries. The effect is very small for average galactic dark matter densities, so detection will be challenging, but gravitational effects like these may be the only way to confirm the nature of dark matter, in the absence of any couplings to standard model particles.

22-Nov-2021: James Cho (CCA), Dynamics of Exoplanet Atmospheres

With thousands of exoplanets now detected, accurate characterization of their atmospheres – in particular, their composition, weather, and climate – has become the next critical step in understanding them. The characterization is not only crucial for understanding current observations, but also for ultimately assessing whether planets can harbour life. In this talk, how atmospheric physics and numerical simulations are used to address these complex problems and what we currently understand about the problems are presented. The presentation will focus on the structure and evolution of ‘exo-storms’ and waves, as well as the variability they induce, which could be observed in current and future missions.

Term 2

17-Jan-2022: Geraint Jones (MSSL), The Comet Interceptor Mission

In 2019, the European Space Agency selected the three-spacecraft Comet Interceptor as a new mission. The project’s primary goal after launch in 2029, with Ariel, is to characterise, for the first time, a long-period comet, preferably approaching the Sun for the first time. This planned flyby promises to provide us with valuable data to complement information gathered by all previous comet missions; all past projects have studied comets that have been altered by passing near the Sun many times. The mission will comprise a main spacecraft and two smaller probes, one of which will be provided by the Japanese space agency, JAXA. We’ll explore the challenges of planning a mission to an unknown target, and the exciting measurements that the mission team plan to make. The mission website is at www.cometinterceptor.space

24-Jan-2022: Azadeh Fattahi (Durham), The build-up of the Milky Way's halo

The hierarchical nature of galaxy formation in the standard model of cosmology (LCDM) predicts a diffuse stellar halo component around Milky Way-mass galaxies, formed from the accretion and disruption of dwarf galaxies. Using cosmological hydrodynamical simulations, I will discuss the radial build up of stellar halos from the accreted dwarfs and will connect these results with recent findings from the Gaia mission related to the major event in the formation history of the Milky Way (Gaia-Enceladus-Sausage). I will discuss whether this event is unusual and whether it has any implications for dark matter distribution and dark matter direct detection experiments.

31-Jan-2022: Rhea-Silvia Remus (USM), The Young and the Wild: What happens to Protoclusters forming at z = 4?

Recent observations have revealed clustered galaxies with extremely high star formation rates at redshifts up to z=7 and higher, which are discussed to be the progenitors of today's most massive galaxies, the BCGs. Using the power of one of the largest hydrodynamical cosmological simulations, Magneticum Pathfinder, I study the evolution and build-up of BCGs and their associated cluster halos since z=7, answering the question how (and if) the extremely star-forming galaxies observed over a wide range of cosmological epochs are linked to present-day BCGs. I will show how the star formation rates at high redshifts are connected to the local positions in the cosmic web; tracing those high redshift systems forward in time, I will show that none of the typical mass indicators at such high redshift are proper tracers to predict the present-day virial mass. Instead, I will present one exception that provides a hint at a more massive outcome of the system at z=0. Finally, I will demonstrate how the massive disk-like galaxies observed at z=2 are connected to present-day BCGs, highlighting the importance of the star-formation epoch for the build-up of the BCGs and their (gaseous) halos.

7-Feb-2022: Paola Pinilla (MPIA/MSSL), First steps of planet formation in the ALMA and JWST era

In this new era of powerful telescopes such as ALMA and JWST, we are now able to study the birth of planets in disks around young stars, in more detail than ever before. New observations are revealing fascinating structures in protoplanetary disks that are transforming our understanding of the formation and evolution of planetary systems. In this talk, I will explain theoretical models of dust evolution in protoplanetary disks and I will compare these theoretical predictions with current multi-wavelength disk observations. This link between models and observations is providing significant insights about how different physical conditions play a crucial role in the formation of the first planetesimals, and is extending our understanding of how initial conditions of protoplanetary disks are reflected in the large diversity of extrasolar systems observed up today.

14-Mar-2022: Jo Maniscalco (In2Science), Improving social mobility through STEM: how you can help youngsters onto the ladder with In2scienceUK

In2scienceUK aims to promote social mobility through improving access to careers in science, technology, engineering and maths for Year 12 students from low-income and disadvantaged backgrounds. This talk will give an introduction to social mobility in the UK and the STEM sector. You'll also hear about the work that In2scienceUK is doing through leveraging the passion of STEM professionals and researchers to host 1 or 2 week work experience placements, and how you can get involved. Apart from being a formative research and learning experience for students, volunteering with In2scienceUK is also an excellent opportunity for volunteer hosts to demonstrate public engagement and supervision, and have fun whilst doing so! Join us to find out more.

Term 3

25-Apr-2022: Helena Bates (NHM), The Winchcombe meteorite

Meteorites offer us a unique opportunity to investigate material from space. Most meteorites come from asteroids, which represent the building blocks of planets, so by studying these rocks we can probe the conditions of our solar system before planets formed. However, meteorites are rare, and often just by sitting on the ground for prolonged periods of time they can be altered beyond recognition. But as luck would have it, in February 2021, a bright meteor was observed over Winchcombe, Gloucestershire, and a meteorite was subsequently recovered from the local area. This was the first recovered UK meteorite fall in 30 years, and I was in the lucky position of being the curator of the national meteorite collection during this event. I will share my experiences of trawling through fields to find samples, documenting every tiny piece that was recovered, and then being part of the consortium first studying them.

9-May-2022: Annagrazia Puglisi (Durham), The rise and fall of star-forming activity in galaxies at cosmic noon

Star-forming galaxies follow a tight correlation in the stellar mass versus star formation rate plane. This so-called “main sequence” is interpreted as evidence that star formation primarily proceeds on long time-scales within extended, clumpy disks across cosmic time, and stochastic processes such as mergers contribute marginally to galaxy growth.  Yet, many questions remain open. For example, it is unclear what are the evolutionary pathways of galaxies in the main-sequence plane, what triggers the high star formation rates observed in starburst galaxies, and what causes galaxies to stop forming stars. I will present our recent efforts in studying galaxies on and above the main sequence at z>1 from an observational perspective, using in particular near-IR spectroscopy and ALMA to measure star formation rates and molecular gas properties. I will discuss these observational results, and their implications for our understanding of star formation and quenching at an epoch when galaxies where forming most of their mass.

16-May-2022: Alan Heavens (Imperial), Field-level inference: the future for cosmology?

Analysis of cosmological survey data is challenging for a host of reasons; post-CMB the fields are not gaussian random fields, and we don’t have a good handle on their statistical properties, so how can we do science?   We can make summary statistics (power spectra, correlation functions etc) and assume their distributions, or more ambitiously build a complete Bayesian hierarchical model for the data.  In this talk I will show how our two BHM programmes, Almanac and BORG-WL, use the full cosmic shear field data in tomographic bins to deliver accurate and precise inference of cosmological parameters, with tests on simulated data giving errors on the matter density a factor 5 smaller than traditional two-point summary statistics.

23-May-2022: Lionel London (KCL), A spheroidal picture for gravitational waves from binary black holes

Central to gravitational wave detection and the inference of source parameters is the representation of gravitational radiation in terms of multipole moments. By construction, these functions of time or frequency allow the radiation's angular dependence to be given by spin weighted harmonic functions. This leaves the radiation itself to be represented as a sum over harmonic functions, whereby each term is weighted by a different multipole moment. The choice of representation, namely the choice of which harmonic functions to use, is not unique. Only the radiation's spin weight must be respected. And while there are multiple appropriate spin weighted functions, only one set of harmonic functions corresponds to the physical system's natural modes. In this talk I will discuss recent and ongoing work regarding a new set of functions that are naturally suited to the modes of astrophysical gravitationally radiating systems. I will outline the mathematical nature of these functions, and comment on their potential use in gravitational wave theory and data analysis.

30-May-2022: Tom Haworth (QMUL), Planet formation in stellar clusters

Star forming regions are hostile environments, with high stellar number densities and strong radiation fields. In addition to feedback from massive stars affecting the evolution of the star forming region itself, it can also affect the evolution of circumstellar discs, which could have implications for planet formation. In this talk I will review recent evidence for the environment influencing disc evolution and discuss some unsolved problems and future prospects.

Seminars 2020/2021

Term 1

21-Sep-2020: Franck Marchis (SETI), First Results with a Network of Small Digital & Smart Telescopes: Citizen Science for Astronomy

Unistellar is building the largest network of compact, easy-to-use, smart and digital telescopes called the Enhanced Vision telescope (or eVscope) with the goal of bringing back to the people the joy of exploring the universe by observing deep sky objects from their home. The SETI Institute is a scientific partner of the project which will develop the scientific applications of this network. To date, ~2000 eVscopes have been shipped and by December the network will be larger than 5,000 eVscopes from citizen astronomers located in Europe, America, Australia, Japan and other places. We are currently developing pilot programs to test the capabilities of the eVscope network to conduct meaningful scientific studies, such as asteroid occultations, transiting exoplanets, Planetary Defense, and the study of comets. First scientific results collected with citizen astronomers in Europe and North America will be presented, this includes the detections of TESS Objects of Interest (TOIs), as well as successful detection of asteroid occultations and lightcurve of main-belt asteroids and near-earth asteroids. Today 10Tb of scientific data have been already collected from hundreds of active citizen astronomers.

We will also discuss the potential of the eVscope at schools (e.g. community colleges in the US) as a tool to learn about astronomy and data processing while bringing space to the classrooms. We will also describe programs with informal education centers (national parks, museums, youth associations) that could become a tool to connect the young generation to astronomy, educate them on the importance of the dark sky and finally demystify science by allowing all of us to participate in the scientific conversation.

28-Sep-2020: Mihkel Kama (UCL), Unlocking the meaning of planetary composition

JWST and Ariel are about to revolutionise our view of the chemical composition of exoplanet atmospheres, while solar system missions are deepening our appreciation of the complex interplay of physical and chemical processes around the young Sun.  Planets build up their total budget of chemical elements as they accrete and migrate in a protoplanetary disk.  The study of the budget of chemical elements in such planet-forming disks is becoming an essential pillar of the exoplanet revolution, with progress facilitated by innovative methods, and telescopes like APEX and ALMA.  I will briefly review recent advances and open questions in disk composition studies, and outline the two complementary approaches through which we aim to advance our understanding of the origin and diversity of planets and life itself.

5-Oct-2020: Jason Sanders (UCL), Our multi-dimensional, time-evolving Galaxy

How galaxies form and evolve over cosmic time is a key question in modern astrophysics. Our current understanding is being driven by results from detailed multi-dimensional observations, both from integral field unit measurements of large samples of nearby galaxies and photometric, spectroscopic and astrometric measurements of individual stars in our own Galaxy. In the Milky Way, we have access to the rich dataset of positions, velocities, abundances and ages for millions to billions of stars. This immense data presents a significant theoretical modelling challenge but also a great opportunity of measuring the detailed dynamical evolution of a single galaxy and forming a complete picture of its history. This enterprise has been brought into focus by results from the Gaia satellite, which has revealed the intricate structure and non-equilibrium nature of our Galaxy.
I will describe recent work on characterising and modelling the evolution of the Milky Way in the era of Gaia. I will discuss new results on three key phases of the Milky Way’s history: 1. the early accretion history of our Galaxy and the impact on the young Milky Way, 2. the formation and properties of the Galactic bar using the very first panoramic view of the transverse velocities of stars in this region and 3. the quiescent late-time dynamical re-structuring of the disc through heating and migration.

12-Oct-2020: Chiara Mingarelli (UConn / Flatiron), Pulsar Timing Arrays: The Next Window to Open on the Gravitational-Wave Universe

Galaxy mergers are a standard aspect of galaxy formation and evolution, and most (likely all) large galaxies contain supermassive black holes. As part of the merging process, the supermassive black holes should in-spiral together and eventually merge, generating a background of gravitational radiation in the nanohertz to microhertz regime.  An array of precisely timed pulsars spread across the sky can form a galactic-scale gravitational wave detector in the nanohertz band. I describe the current efforts to develop and extend the pulsar timing array concept, together with the recent  NANOGrav 12.5 year "hint" of a signal, and how this can be used to constrain astrophysical phenomena at the heart of supermassive black hole mergers.

19-Oct-2020: Zama Katamzi-Joseph (SANSA), Waves in the Earth’s ionosphere

Traveling ionospheric disturbances (TIDs) are signatures of atmospheric gravity waves that commonly occur in the ionospheric F-region. In this seminar we will look at the brief history of TID studies conducted at the South African National Space Agency (SANSA) before presenting a climatology of medium scale TIDs (MSTIDs). This climatology was obtained using night-time airglow intensity measurements from an all-sky camera located at Sutherland, South Africa (32.4˚ S, 20.8˚ E; magnetic latitude 40.7˚ S). This climatology reveals that MSTIDs occur in all seasons but predominantly during the winter months, and mostly propagate in the westerly direction with speeds of 17—165 m/s. Their periods and wavelengths range are 19—70 minutes and 58—252 km, respectively. Analysis of neutral wind measurements from a co-located Fabry-Perot interferometer (FPI) showed that this favoured propagation direction was the least constricted by neutral winds.

26-Oct-2020: Keith Hawkins (UT Austin), Galactic Archaeology with Gaia and Large Spectroscopic Surveys

One of the key objectives of modern astrophysics is to understand the formation and evolution galaxies. In this regard, the Milky Way is a critical testing ground for our theories of galaxy formation. However, dissecting the assembly history of the Galaxy, requires a detailed mapping of the structural, dynamical, chemical, and age distributions of its stellar populations.  Recently, we have entered an era of large spectroscopic and astrometric surveys, which has begun to pave the way for the exciting advancements in this field. Combining data from the many multi-object spectroscopic surveys, which are already underway, and the rich dataset from Gaia will undoubtedly be the way forward in order to disentangle the full chemo-dynamical history of our Galaxy. In this talk, I will discuss my current work in Galactic archaeology and how large spectroscopic surveys have been and can be used to dissect the structure of our Galaxy. I will also explore the future of Galactic archaeology through chemical cartography.

2-Nov-2020: Ting Li (Carnegie Observatories / University of Toronto), The Southern Stellar Stream Spectroscopic Survey: Overview and Latest Science Results

The Southern Stellar Stream Spectroscopic Survey (S5) is an ongoing spectroscopic program that maps the newly discovered stellar streams with the fiber-fed AAOmega spectrograph on the Anglo-Australian Telescope (AAT). S5 is the first systematic program pursuing a complete census of known streams in the Southern Hemisphere, providing a uniquely powerful sample for understanding the building blocks of the Milky Way's stellar halo, the progenitors and formation of stellar streams, the mass and shape of the Milky Way's halo, and ultimately the nature of dark matter. The survey started in Summer 2018 and have mapped 14 streams with ~45 nights on AAT. In this talk, I will give a brief overview of the current status of the program, highlighting the latest science results from the survey, and end the talk with the public data release plan.

16-Nov-2020: Tom Charnock (IAP), Machine learning, statistics and the relation between neural networks and physics

Based on my current research into the statistical interpretation of modern machine learning methods, I will present the connection between machine learning, in particular the use of neural networks, and scientific model building. By understanding neural networks in the form of statistical models I will show why they are so adept for tackling current physical problems, but I will also highlight their limitations in terms of comprehensibility and scientific understanding and safety. From this perspective I will suggest where these modern techniques could be useful to pursue further, but overall finish on a slightly skeptical note about where these methods can take us for science. The studies presented can be viewed in the Artificial Intelligence for Particle Physics book chapter - Bayesian neural networks (https://arxiv.org/abs/2006.01490) as well as several blog posts including https://medium.com/@tom_14692/all-deep-learning-is-statistical-model-building-fc310328f07

23-Nov-2020: Sam Thompson (Cavendish Labs), Terra Hunting Experiment: Finding another Earth with HARPS3

The Terra Hunting Experiment is a 10-year radial-velocity (RV) search designed to discover Earth-mass planets on long-period, Earth-like orbits, around our nearest Solar-like stars.  To undertake this programme, we are currently building the High Accuracy Radial-velocity Planet Searcher 3 (HARPS3), an R = 115,000 echelle spectrograph, which will be operated in a robotic mode on the refurbished 2.5m Isaac Newton Telescope.  In this talk I will discuss some of the challenges we need to meet in order to push our detection threshold to 10 cm/s - the RV semi-amplitude of an Earth-like planet.  I will also present an overview of the HARPS3 instrument and describe our strategy for the Terra Hunting Experiment.

7-Dec-2020: Marcelle Soares-Santos (University of Michigan), Cosmology in the era of multi-messenger astronomy with gravitational waves

Motivated by the exciting prospect of a new wealth of information arising from the first observations of gravitational and electromagnetic radiation from the same astrophysical phenomena, the Dark Energy Survey (DES) has established a search and discovery program for the optical transients associated with LIGO/Virgo events (DESGW). Using the Dark Energy Camera (DECam), DESGW has contributed to the discovery of the optical transient associated with the neutron star merger GW170817, and produced the first cosmological measurements using gravitational wave events as standard sirens. After three successful observing campaigns, I present, in this talk, an overview of our results and their implications for the emerging field of multi-messenger cosmology with gravitational waves and optical data.

Term 2

11-Jan-2021: Seshadri Nadathur (UCL), Unveiling the dark side with cosmic voids

New galaxy surveys will soon provide us unprecedented maps of structure in the cosmic web. This data contains a wealth of information beyond what can be extracted using traditional methods based on two-point statistics and power spectra. Using cosmic voids – vast regions deficient in galaxies – is one particularly promising new technique. I will describe how they can be used to measure gravitational effects on light propagation, the growth rate of structure, and – in particular – to improve distance measurements by a factor of 2. I will show current results from the completed BOSS and eBOSS surveys, and describe the prospects with DESI and Euclid in the next few years.

18-Jan-2021: Jo Bovy (UoT), Constraining the nature of dark matter with stellar streams in the Milky Way

Stellar tidal streams originating from disrupting globular clusters in the Milky Way’s halo hold enormous promise as probes of both the large-scale structure of the Milky Way halo’s density distribution and its small-scale structure. As such, the observed density, spatial, and kinematic structure of stellar streams can provide important new constraints on the interactions and small-scale structure of dark matter. I will discuss recent progress on modeling the dynamics of stream formation and its application to fitting observed stellar stream data from photometric, spectroscopic, and astrometric observations. I will in particular focus on how the most recent photometric and astrometric data (from Gaia) helps us map the small-scale structure of streams and how this lets us answer the fundamental question: Is dark matter cold?

25-Jan-2021: Joe Silk (IAP/Oxford), The Future of Cosmology

One of the greatest challenges in cosmology is understanding the origin of the structure of the universe. The fossil radiation from the beginning of the universe, the cosmic microwave background, has provided a unique window for probing inflation and the initial conditions from which structure evolved. Large surveys of galaxies have provided complementary information that has enabled us to reach the era of precision cosmology, with parameter determination approaching percent level accuracy.  But where do we go next? Future experiments are planned with the next generation of observatories that will increase this precision by at most an order of magnitude. However, we need to do far better if there is to be a guaranteed science return that will definitively probe our cosmic origins. I shall argue that the ultimate goal for our future strategy must be astronomy from lunar-based telescopes, and I will provide several examples of what could be accomplished within the next two decades.

1-Feb-2021: Nicole Pawellek (Cambridge), Fast and Furious - Debris Discs in the beta Pic Moving Group

Only 20% of old field stars have detectable analogues to our Asteroid and Kuiper belts which are called debris discs. This leaves open the question of what disc, if any, is present around the remaining 80%. Young moving groups allow to probe this population, since discs are expected to have been brighter early on. We consider the population of F stars in the 23 Myr-old BPMG where we find that 9/12 targets possess discs. Comparing the BPMG results to disc samples from ∼45 Myr and ∼150 Myr-old moving groups, and to discs found around field stars, we find the disc incidence rate in young moving groups is comparable to that of the BPMG and significantly higher than that of field stars. We also find that the disc luminosities in the populations considered drop by two orders of magnitude within the first 100 Myr. This is much faster than expected by collisional evolution! We attribute this depletion to embedded planets which would be around 170 M_earth to cause a depletion on the appropriate timescale. However, we cannot rule out that different birth environments of nearby young clusters result in brighter debris discs than the progenitors of field stars which likely formed in a more dense environment.

8-Feb-2021: Hannah Wakeford (Bristol), Observing Alien Atmospheres

The study of exoplanets, planets that orbit stars other than the Sun, is at the forefront of the public imagination in space and an exciting field of research. The question "how do stars and planetary systems form and evolve?"" is one of the biggest in Astronomy, and is at the root of one of the most important questions in science today: "How did we get here?". To resolve these questions we need to observe, interpret, and understand the nature of planets beyond our Solar System.

In this talk I will go through the methods, observations, and the physics behind some of the interpretations we are making about the nature of these strange new worlds. As an observer I will show some of the work we have been doing measuring the transmission spectra of giant exoplanet atmospheres looking for the tale-tale absorption of water vapor and the presence of exotic clouds.  I will discuss some of the challenges associated with the measurement of atmospheric abundances, a brief look at the role clouds can play in understanding dynamics and chemistry, and what future measurements can help further constrain our understanding of planetary atmospheres.

22-Feb-2021: Claudia Gutierrez (Turku), Hydrogen-rich supernovae: understanding their explosion and progenitor properties

Hydrogen-rich supernovae (type II Supernovae; SNe II) are produced by the final explosions of massive stars (>8-10 Msun ), which retain a significant part of their hydrogen envelopes before the explosion. These SNe show a large diversity in their transient behaviour, which is likely determined by differences, not just in explosion properties, but also in the progenitor star characteristics. In this talk, I will present the current status of SNe II studies. I will focus on new results found with a sample of SNe II occurring within low-luminosity galaxies. I will also describe the challenges in the determination of the explosion and progenitor parameters for these objects.

1-Mar-2021: Gianrico Filacchione (INAF, Rome), The characterization of comet 67P/CG nucleus by means of VIS-IR imaging spectroscopy

In this seminar a review of the main results achieved by the Visible, Infrared and Thermal Imaging Spectrometer (VIRTIS) aboard ESA’s Rosetta mission [1] are given. The instrument, operating at both visible (0.23-1 µm) and infrared (1-5 µm) wavelengths, has returned spatially-resolved data of asteroids 2867 Steins and 21 Lutetia observed during two fast flybys occurred during the mission cruise phase and of 67P/Churyumov-Gerasimenko comet, Rosetta's main scientific objective, which has been continuously explored for 26 months during its perihelion passage. Once at 67P, VIRTIS has characterized the overall nucleus surface composition which appears made by an assemblage of organic matter, refractories and ices forming a very dark (albedo 0.06) surface dust layer. Thanks to the high spatial resolution achieved by VIRTIS (up to about 2.5 m/px) exposed water ice and carbon dioxide-rich ares have been identified on the surface and correlated with local morphology. Moreover, time-resolved observations have allowed to study diurnal and seasonal evolution of the surface and nearby coma particles showing temperature and composition trends with heliocentric distance. These results demonstrate how visible and infrared imaging spectroscopy techniques are capable to infer composition and physical properties of surface’s regolith and to correlate this information with morphological and geological features on maps. By resolving diagnostic bands associated to vibrational modes, inversion methods based on radiative transfer theory allow to recognize minerals, organic materials, salts, and ices of different composition, their mixing modalities (areal, intimate, intraparticle), grain size distribution, surface roughness, medium porosity, surface temperature and thermal inertia. For these reasons, VIS-IR imaging spectrometers remain a high-gain scientific payloads proficient in maximizing the scientific return from any future asteroid and cometary mission.

8-Mar-2021: Gabriela Calistro Rivera (ESO), The multiwavelength properties of red QSOs - Evidence for dusty winds as the origin of QSO reddening

An outstanding question on the nature of quasars (QSOs) is to understand what is the origin of QSO reddening. This question is motivated by the fundamental differences found in the radio properties of red QSOs as compared to blue QSOs, positioning red QSOs as a potential key population in the context of galaxy and black hole evolution. In this seminar, I will present a systematic study of the multiwavelength (radio-to-UV) properties of SDSS quasars at 0.2<z<2.5, classified into red and control QSOs and matched in redshift and luminosity.

Capitalising on rich multi-wavelength ancillary data sets, we analysed their optical spectral properties and modelled the panchromatic spectral energy distributions (SEDs) using the SED-ftting code AGNfitter. We inferred parameters driving the physics of QSO accretion, obscuration, and outflow properties, as well as interstellar medium and star formation properties of their host galaxies, in order to identify any signature that elucidate the scales in which the reddening in QSOs is originated. We discovered a higher incidence of high-velocity wind components in nuclear emission lines in red QSOs, connected to a hot-dust emission excess detected at 2-5 um that cannot be explained by torus emission models. This finding provides indirect evidence for the scenario where the presence of dusty winds at nuclear scales are potentially the physical ingredient responsible for the optical colours in red QSOs, as well as a key parameter for the regulation of accretion material in the nucleus.

22-Mar-2021: Yashar Hezafeh (Montreal), Probing the particle nature of dark matter with strong gravitational lensing

The nature of dark matter is one of the most important outstanding questions in modern cosmology and astrophysics. Uncovering the properties of the dark matterparticle could result in significant leaps in our understanding of fundamental physics and impact numerous astrophysical models. It is well understood that the microphysics of the dark matter particle impacts its clustering properties on different scales. The most widely accepted dark matter model, cold dark matter, has had tremendous success explaining the large-scale structure of the universe. However, it has faced many challenges for its predictions of the distribution of matter on small, sub-galactic scales, with some observations seemingly favoring a warm dark matter alternative. A definitive answer to this question can only be achieved by mapping the distribution of dark matter on small scales with a purely gravitational probe. Strong gravitational lensing is the only probe capable of doing this at cosmological distances. In this talk, I will discuss how the discovery of a new population of strong gravitational lenses, a new observatory, ALMA, and new advances in analysis methods are allowing us to map the distribution of darkmatter on small scales with high precision. In the coming years, thousands of new lenses from large surveys (e.g., LSST), existing and new facilities (e.g., ALMA, JWST, TMT), and new analysis methods (machine learning) will transform this field, allowing us to understand the small-scale behavior of dark matter with unprecedented accuracy and precision, opening a new window for testing dark matter models in a previously inaccessible regime.

Term 3

10-May-2021: Ferah Munshi (Oklahoma), Can we constrain dark matter at the limits of galaxy formation?

Dwarf galaxies provide a very important and intriguing laboratory for the study of dark matter physics. I will present results from extremely high resolution, fully cosmological simulations that contain many isolated dwarf galaxies [the MARVELous dwarfs] as well as satellite dwarf galaxies [the DC Justice League]. Together, they create the largest collection (211) of high-resolution simulated dwarf galaxies to date and the first collection to resolve ultra-faint dwarf galaxies in multiple environments. With this flagship suite I can statistically characterize dwarf galaxies in order to constrain dark matter physics. I will present results answering the following key question: What testable predictions can we make to constrain dark matter at the lowest dwarf masses?

17-May-2021: Sara Ellison (Victoria), Gas and star formation in the nearby universe with the ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey

Understanding the processes that regulate star formation in galaxies remains at the heart of modern extra-galactic astronomy, and debate continues as to why some galaxies exhibit powerful starbursts whilst others are largely dormant.  The key to progress in this arena lies with assembling large, diverse samples of galaxies for which we can measure all of the critical ingredients, such as the current star formation rate (SFR) and gas content.  However, it is insufficient to simply measure global galactic quantities, as we know that a given galaxy will manifest considerable internal diversity in its star formation activity.  It is therefore essential to study gas and star formation on spatially resolved scales.  The ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey combines maps of stellar properties obtained from the MaNGA (optical) integral field unit survey with ALMA CO (1-0) maps on a common kpc-scale grid, in order to tackle questions of star formation in local galaxies.  The 46 galaxies in the ALMaQUEST sample span a wide range of SFRs, including both normal star forming galaxies, as well as those both on their way to quenching, and those undergoing starbursts.  In this talk, I will present the ALMaQUEST view of understanding the interplay of gas and star formation across this broad galactic landscape.

24-May-2021: Rebecca Smethurst (Oxford), The growth of supermassive black holes in the absence of mergers and the effect on their host galaxies

The co-evolution of galaxies and their supermassive black holes (SMBHs) via mergers is a long-held paradigm that has recently been overturned. With a sample of `bulgeless’ disk-dominated galaxies Simmons, Smethurst & Lintott (2017) showed that in the absence of mergers, SMBHs can grow to 10^9 solar masses. A follow up study by Martin et al. (2018) found that in simulations, 65% of all the matter contained in SMBHs at z~0 was acquired through non-merger processes. We now present narrow band imaging of the [OIII] 5007 Å component for 12 of these `bulgeless’ disk-dominated galaxies hosting luminous, unobscured AGN with spectrally confirmed blue shifted outflows, presumed to be powered by the AGN itself. These massive galaxies’ formation histories are dominated by non-merger secular processes and thus provide a unique opportunity to study how inflows from secular processes fuel significant growth of black holes in the absence of significant mergers. We have constrained this contribution from secular processes by using the luminosity and extent of the [OIII] 5007 Å outflow in the narrow band images to measure the rate of mass loss in outflows from the central AGN of these disk-dominated galaxies. By combining these measurements with spectroscopically derived data constraining the black hole accretion rates, we have placed a limit on the total inflow rate to the centre of these galaxies. Further analysis of these systems with integral field spectroscopy techniques offers the promise of directly measuring the black hole growth that is occurring in present day systems evolving solely via secular evolution, and the impact of AGN feedback in such systems due to outflows.

Seminars 2019/2020

Term 1

30-Sep-2019: Iary Davizon (DAWN/NBI), Machine learning for skeptical astronomers

A new generation of machine learning codes is becoming ubiquitous in the literature, and seminal studies indicate they may allow us to solve long-standing astrophysical problems. However, such great expectations may not be fulfilled because of the "black box" nature of most of these algorithms, inextricable biases in their training sample, and other limitations. Sharing these concerns, we tested unsupervised "manifold learning" algorithms with a realistic mock galaxy catalog (up to z=4) derived from cosmological hydro-dynamical simulations. I will present the results we obtained by analyzing this data with self-organizing maps (SOMs), and discuss the groundbreaking applications the SOM may have in understanding galaxy formation and evolution. I will highlight general aspects of  manifold learning that can be also useful in other areas of Astrophysics, but also the open issues that still justify some skepticism.

7-Oct-2019: Nadia Blagorodnova (Radboud), Common-envelope transients: buried in the infrared

Most stars in our Universe live in binaries.  Unstable mass transfer from one star to another can lead to the formation of a shared gaseous shell where both stars orbit: the common envelope. The end of this phase is marked by the quick spiral-in of the secondary star towards its companion, leading to violent interactions between the components. The whole, or part of the binary's common envelope may get ejected, and the pair may even completely merge. This last phase has been serendipitously witnessed as astrophysical transients called luminous red novae (LRNe), allowing us to study the progenitor stars, the energetics of the outburst and the properties of the ejected material. In my talk, I will provide an overview of LRNe, their progenitor systems and their main formation scenarios, explored by recent theoretical models. Observations of these common-envelope transients show that, while the emission quickly fades in the optical bands, their infrared signatures remain bright, revealing the formation of cold dust shells reprocessing the light of the newly coalesced star.

14-Oct-2019: Jens Chluba (Manchester), Spectral distortions in CMB

Following the pioneering observations with COBE in the early 1990s, studies of the cosmic microwave background (CMB) have primarily focused on temperature and polarization anisotropies. CMB spectral distortions – tiny departures of the CMB energy spectrum from that of a perfect blackbody – provide a second, independent probe of fundamental physics, with a reach deep into the primordial Universe. The theoretical foundation of spectral distortions has seen major advances in recent years, which highlight the immense potential of this emerging field. Spectral distortions probe a fundamental property of the Universe – its thermal history – thereby providing additional insight into processes within the cosmological standard model as well as new physics beyond. Spectral distortions are an important tool for understanding inflation and the nature of dark matter. They shed new light on the physics of recombination and reionization, both prominent stages in the evolution of our Universe, and furnish critical information on baryonic feedback processes, in addition to probing primordial correlation functions at scales inaccessible to other tracers. I will provide a broad brush overview of the exciting opportunities awaiting us using CMB spectral distortions.

21-Oct-2019: Peter Laursen (Univ. of Oslo), Lyman α — a window to the distant Universe

Lyman α is the most common type of light emitted from the most common element in the Universe and is hence used to study galaxies across the entire Universe. Being sensitive to many different physical processes — such as gas temperature, dust contents, galactic outflows, and intergalactic ionization state — it is simultaneously extremely informative and notoriously hard to interpret. Most of the Lyman α emitted from galaxies is related to newly formed stars, but a significant fraction is expected to be emitted from the gas feeding the galaxies from the surrounding intergalactic medium, cooling as it plummets down the potential well of the galaxy. Whereas the former is observed regularly, detection of the latter is challenging, and as yet the evidence for its existence is at best tentative. In this seminar, I will review the wonders and pitfalls of Lyman α, and present work-in-progress analytical estimates of the amount of cooling radiation.

28-Oct-2019: Jonathan Tan (Chalmers), A Light in the Dark - Massive Star Birth Through Cosmic Time

Massive stars have played a dominant role in shaping our universe since its earliest times, but there is still no consensus on the mechanism by which they form. I review the physics that is important for massive star formation and the connection this process may have with star cluster formation. I then focus on a particular theoretical model, Turbulent Core Accretion, which assumes the initial conditions are massive, turbulent, magnetized cores of gas and dust that are reasonably close to virial equilibrium. Our group has been exploring this scenario via analytic models and numerical simulations of the physics and chemistry of the interstellar medium, ranging from the earliest pre-stellar core phase to protostellar cores being impacted by strong self-feedback. Crucially, these models can now be tested in detail with ALMA, SOFIA and other facilities, and I present the latest results from multiple projects that are zooming in to massive star birth in the darkest shadows of giant molecular clouds. Extension of this work has the potential to also determine how the full stellar initial mass function is established across different Galactic environments. Finally, I discuss an application of massive star formation theory to the early universe: how massive were the first stars and could they have been the progenitors of supermassive black holes?

4-Nov-2019: Sarah Rugheimer (Oxford), Ultraviolet, Biosignatures and Life

When we observe the first terrestrial exoplanet atmospheres, we expect to find planets around a wide range of stellar types, ultraviolet environments, and geological conditions. Since the first exoplanets available for characterization will be likely for M dwarf host stars, understanding the ultraviolet environment of these cool stars is a vital step in understanding the atmospheres of these planets. Additionally the atmospheres of these planets will not been fixed in time. Earth itself offers many possible atmospheric states of a planet. We set out to examine how an Earth-like planet at different geological epochs might look around other star types Additionally, we examine the plausibility of detecting prebiotically interesting molecules, such as HCN, NH3, CH4, and C2H6 in an early-Earth type atmosphere around stars with very different ultraviolet environments, an M dwarf and a solar analogue.

18-Nov-2019: Mickael Rigault (CNRS), Astrophysical biases of Type Ia Supernovae and the Hubble Constant

Type Ia supernova are powerful cosmological distance indicators that enable us to measure the expansion history of the Universe. Using SNe Ia distances, scientists discovered the accelerating expansion of the Universe, leading to a Nobel prize and a broad focus on understanding the underlying cause of this acceleration.  SNe Ia distances are also key to measuring the Hubble Constant, the current expansion rate of the Universe and a key cosmological parameter.  Interestingly, the SNe Ia measurements of H0 are ~5 sigma away from the those derived from CMB temperature anisotropy measurements from Planck.  This highly discussed tension could be a sign of new physics, though no simple theoretical models are able to explain it.  However, I will discuss how recent studies of SNe Ia in the nearby Universe indicate two separate populations of SNe Ia with different peak luminosities. These differences in the underlying SNe Ia population could introduce a bias in the derived H0 and be the true cause of the tension with CMB measurements.

2-Dec-2019: Luca Fossati (Graz), Planet atmospheric escape: a tool for understanding both stars and planets

Planets in short-period orbits provide a unique opportunity to directly study atmospheric escape, which is a phenomenon having a profound impact on our understanding of the observed exoplanet demographics. Among all planets known to have an escaping atmosphere, those undergoing extreme mass loss are key: their escape may be representative of young planets, at a time when atmospheric escape matters most. I will briefly review our knowledge and understanding of planet atmospheric escape and present four concrete examples of how studying this phenomenon can bring forward our knowledge of both planets and stars. I will then conclude presenting a new upcoming facility for the study of planetary upper atmospheres and escape.

Term 2

20-Jan-2020: Stephen Feeney (UCL), Clarifying the Hubble Constant Tension

Our best estimate of the Universe's current expansion rate (the Hubble constant) from the local Universe (via the Cepheid distance ladder) is in four-sigma tension with the value extrapolated from cosmic microwave background data assuming the standard cosmology. Whether this discrepancy represents physics beyond the Standard Model or deficiencies in our understanding of the data is the subject of intense debate. In this talk, I will review the community's attempts to explain and interpret the Hubble constant tension, clarifying the current picture using Bayesian probability theory, and consider the potential for independent gravitational wave observations to arbitrate the dispute.

3-Feb-2020: Megan Bedell (Flatiron), Investigating the Star-Planet Connection with Precision Spectroscopy

More than two decades after the discovery of the first exoplanet with radial velocity (RV) measurements, large quantities of data exist from dedicated planet-hunting spectrographs. These spectra play an important role not only in the discovery and characterization of planets but also as a rich source of information about bright stars in the solar neighborhood. I will summarize recent efforts to gain insight into the planet formation process via extremely precise (0.01 dex) abundance measurements of solar twin stars with and without planets. I will also discuss approaches to the data analysis challenge of extracting maximally-precise RV measurements from these spectra in pursuit of Earth-like planets.

10-Feb-2020: Chiara Circosta (UCL), Looking for observational signatures of feedback from active galactic nuclei

Supermassive black holes, residing in the centre of massive glaxies, grow through accretion of gas and become visible as active galactic nuclei (AGN). The extraordinary amount of energy injected into the interstellar medium during these accretion episodes is thought to be key in shaping the life cycle of host galaxies and regulating star formation, via the so-called AGN feedback. The impact of AGN is expected to be maximised at z~2, i.e. the peak of supermassive black hole and galaxy assembly. Despite the wide observational support that AGN drive outflows into their host galaxies, a comprehensive picture is still missing. Moreover, measuring the gas content out of which stars form is necessary to understand how AGN regulate star formation. In this talk I will describe our efforts in performing a systematic study of AGN outflows by using integral field spectroscopy as well as characterising the molecular gas reservoir of the host galaxies through an ALMA campaign. Eventually our work will create a detailed picture of how AGN affect star formation in their host galaxies.

17-Feb-2020: Konrad Kuijken (Leiden), Cosmology from gravitational lensing with the Kilo-Degree Survey

The Lambda-CDM model is a very succesful description of the universe. It predicts how large-scale structures form and grow with time, leading to the present-day population of clustered galaxies. In this talk I will describe how we are testing this model with gravitational lensing measurements of the large-scale distribution of matter, in particular from the Kilo-Degree Survey, a project to map 1300 square degrees of sky using the VLT Survey Telescope at ESO in Chile.

24-Feb-2020: Clara Sousa Silva (MIT), Finding an Alien Biosphere with Computational Chemistry

At the edge of our present scientific frontier lies the question: “Can we identify the signs of life on an exoplanet?”. Establishing whether a planet is habitable, or inhabited, relies both on the observation of an exoplanet atmosphere and, crucially, its subsequent interpretation. This interpretation requires knowledge of the spectral behavior of every significant atmospheric molecule. However, though thousands of molecular candidates can contribute towards the spectrum of an atmosphere, data exist for only a few hundred gases. Among these, only a fraction have complete spectra (e.g. ammonia, water). This deep incompleteness in the knowledge of molecular spectra presents a pressing vulnerability in the atmospheric study of planets; there exists a strong possibility of mis-assignment, false positives, and false negatives in the detection of molecules.
The work presented here combines structural organic chemistry and quantum mechanics to obtain the necessary tools for the interpretation of astrophysical spectra and, ultimately, the detection of life on an exoplanet. Whether alien life will produce familiar gases (e.g., oxygen) or exotic biosignatures (e.g., phosphine), painting a confident picture of a potential biosphere will require a holistic interpretation of an atmosphere and its molecules. In this talk Clara will describe the ongoing efforts to decipher exoplanet atmospheres through the identification of volatile molecules, in particular those that might be produced by non-Earth-like life on exoplanets.

23-Mar-2020: Rita Tojeiro (St Andrews), The galaxy-halo connection in the cosmic web

Over the last two decades, extragalactic surveys have mapped the positions of millions of galaxies over extraordinary volumes, in an effort to understand the dynamics, composition and underlying rules that govern our Universe. Galaxies and the dark matter halos in which they reside are intrinsically connected, and that relationship holds information about important processes in galaxy and structure formation: understanding it is key to unlocking the full statistical power of forthcoming redshift surveys and their cosmological analyses. In this seminar, I will consider how the galaxy-halo connection might depend on its position within the cosmic web - the familiar decomposition of large-scale structure in filaments, knots and voids. I will finish by introducing the forthcoming DESI survey, and the role DESI will play in unravelling the galaxy-halo connection within the cosmic web.

Term 3

27-Apr-2020: Tessa Baker (QMUL), Testing Gravity with Gravitational Waves

Gravitational waves (GWs) have already proved immensely powerful for constraining cosmological extensions of GR, both from data-driven and theoretical perspectives. However, GWs really come into their own when used in combination with complementary electromagnetic data. I’ll review some of the latest bounds on modified gravity from GWs, and look at how the remaining gravity parameter space can be tested with future experiments like LISA and accompanying galaxy surveys.

11-May-2020: Freeke van de Voort (Cardiff), Cosmic gas flows in the circumgalactic medium around Milky Way-like galaxies

Galaxies are intimately connected to the environments they live in. The haloes around them contain the gas reservoir from which the galaxies grow, while galactic outflows heat and enrich this 'circumgalactic medium' (CGM). In this talk, I will use cosmological, magnetohydrodynamical simulations to study the physical and observable properties of the gas around galaxies. We use a new simulation refinement technique to reach orders of magnitude higher resolution than the current state-of-the-art. Our spatially refined simulations show that the CGM has more 'cool' gas than previously thought, which strongly affects predicted observables in the CGM: The neutral hydrogen (HI) column densities are dramatically enhanced, more in line with observations. I will show how the presence of magnetic fields alters the gas flows into and out of galaxies, resulting in less mixing and higher gas fractions inside the halo. I will briefly discuss the effects on the galaxies themselves.

18-May-2020: Adam Amara (Portsmouth), Forward Modeling the Universe: Application to Cosmic Shear

Observational cosmology is going through a golden age. In particular, we are in the midst of an influx of data from on-going experiments, such as the Dark Energy Survey (DES). In the coming five years, the volume and quality of data will rapidly increase as Stage IV surveys, Euclid, LSST and WFIRST, come online. Processing this data will require new algorithms and methods to maximise our science reach and to control for systematic errors. In this talk, I will present a method that we have developed called Monte-Carlo-Control-Loops that relies heavily on forward modelling the observed data by simulating all the processes from cosmology theory to images. Given the complexities of the late-time Universe, these forward models need to capture the important properties of galaxy populations and key features imprinted on the data from the experiments themselves. By bringing together all these elements with advanced statistical methods and new machine learning algorithms, we can build a process for extracting maximal information from the new data, which will allow us to extensively test the physics of the dark sector.