Georgia de Nolfo, NASA/Goddard
Understanding High Energy Solar Energetic Particles with PAMELA
Despite the signiﬁcant progresses achieved in recent years, the physical mechanisms underlying the origin of Solar Energetic Particles (SEPs) are still matter of debate. The complex nature of both particle acceleration and transport poses challenges to developing a universal picture of SEP events over a wide range, encompassing the low energy observations by space-based instruments and the Ground Level Enhancement (GLE) data by the worldwide network of neutron monitors. The high precision data collected by the PAMELA satellite experiment oﬀer the unique opportunity to study the SEP ﬂuxes between ∼80 MeV and a few GeV, signiﬁcantly improving the characterization of the most energetic events. In particular, PAMELA can measure for the ﬁrst time with good accuracy the spectral features at moderate and high energies, providing important constraints for current SEP models. Reported results are consistent with diﬀusive shock acceleration theories predicting spectral roll-overs attributed to particles escaping the shock region during acceleration. In addition, the PAMELA mission can investigate the relationship between low and high energy events, enabling a clearer view of SEP origin. No qualitative distinction between the spectral shapes of GLE, sub-GLE and non-GLE events is observed, suggesting that GLEs are not a separate class, but are part of the global distribution of SEP events, populating the most energetic subset of a continuous spectrum.
Anne-Marie Broomhall, Warwick
Seismological insights into the magnetic activity of the Sun and other stars
Many mysteries surround the Sun’s magnetic field, which varies in strength, primarily on a time scale of 11yrs. The Sun’s magnetic field is generated by a dynamo in its interior but models of the solar dynamo remain uncertain and diverse. In this talk I will discuss how helioseisomology can provide crucial insights into the Sun’s enigmatic magnetic field. Helioseismology uses the Sun’s natural acoustic oscillations to study the Sun’s interior. The properties of helioseismic oscillations are affected by the presence of a magnetic field and so by studying variations in the oscillations through the solar cycle we can learn about the Sun’s internal magnetic field. I will show how modelling the impact of magnetic fields on these oscillations can lead to insights into the strength and structure of the subsurface magnetic field. We are now in a position where we have helioseismic observations of multiple cycles: I will review recent results that suggest the relation between the Sun’s internal magnetic field and manifestations on the surface and in the atmosphere are not constant from one cycle to the next. I will also demonstrate that helioseismology is a valuable tool in discriminating small changes in the magnetic field, such as those seen at cycle minima. Similar techniques can be used to study the magnetic activity cycles of stars other than the Sun (through asteroseismology), using data from, for example, NASA’s Kepler satellite. I will describe the synergies and differences between signatures of magnetic activity on the Sun and other stars and will discuss how typical a star the Sun really is.
Renske Smit, Cambridge
A panchromatic view of galaxies during the cosmic dawn
During the first few billion years of cosmic time the first galaxies form. As these systems grow, they are thought to reionize the pervading neutral gas in the Universe. In the last decade, large samples of these galaxies have been identified with the Hubble Space Telescope. Despite this remarkable progress, the physical properties of these galaxies are still largely unknown. I will describe the step-by-step progress that has been made over the last fews years in uncovering the stellar populations, radiation fields and even the first dynamical measurements of some of these earliest-known sources of light in the Universe.
Min Du, Beijing
The effect of nuclear bars on kinematics, dynamics, and black hole growth of spiral galaxies
It is well known that bar structures play important roles in driving the secular evolution of spiral galaxies. About one-third of barred galaxies maintain a nuclear bar of sub-kiloparsec radius. Observations using integral field unit (IFU) spectroscopy show that nuclear bars can significantly affect kinematics and dynamics at the central region of galaxies. Such “bars-within-bars” systems have also been hypothesized to be an important mechanism for driving gas inflows efficiently to small scale, thus feeding central BHs in the secular evolution. I will introduce our recent simulation result of the effect of nuclear bars on kinematics, dynamics, and growth of black holes.
Richard Hull, UCLan
The Grenfell Tower Fire: A very British Tragedy
The Grenfell Tower fire, which killed 70 people in June 2017, shocked the world. How could a fire spread so rapidly around the outside of a building in one of the wealthiest parts of the globe? The external face of many of today’s buildings are covered with visually attractive, weatherproofing, insulation systems. The UK is unusual in permitting the use of combustible materials in such façade systems, even on high-rise buildings. We have investigated the range of product types available for façade systems, and shown very large differences in flammability and fire toxicity between the different products. Our bench-scale methods proved more effective in assessing the hazards from fire of the façade systems than any of the currently available regulatory tests in use in the UK.
Rebecca Smethurst, Nottingham
The co-evolution of galaxies and supermassive black holes: the search for observational evidence of AGN feedback
The nature of the observed co-evolution of galaxies and their central supermassive black holes and the effects of AGN feedback on galaxies are two of the most important open issues in galaxy evolution. I shall present a review of galaxy quenching techniques and highlight the results of my own work using a new Bayesian analysis to understand the big picture of quenching and galaxy-black hole co-evolution. In particular I shall show the results of an analysis of the morphological dependent quenching history of a population of Type 2 AGN galaxies in comparison to an inactive population. These results show Type 2 AGN host galaxies having undergone a recent (within 2 Gyr) and rapid drop in their star formation rate. AGN feedback is therefore important at least for this population of galaxies, however the diversity of this method also highlights that histories of rapid quenching cannot account fully for the quenching of all the star formation in a galaxy’s lifetime across the population of AGN host galaxies. I shall discuss how these results show that both merger-driven and non-merger processes are contributing to the co-evolution of galaxies and supermassive black holes and how this relates to galaxy environment and stellar kinematics. The availability of gas in the reservoirs of a galaxy, and its ability to be replenished, appear to be the key drivers behind this co-evolution.
Amery Gration, Leicester
Dynamical modelling of dwarf-spheroidal galaxies using Gaussian-process emulation
The dwarf-spheroidal satellites of the Milky Way are some of the most dark-matter dominated systems known, and are widely recognized as valuable laboratories in which to study the properties of dark matter. Observations of the stellar kinematics of several dwarf spheroidals have yielded data sets of several thousand individual stellar velocities. However, dynamical modelling of dwarf spheroidal galaxies has been based on very restrictive simplifying assumptions, namely that the dwarfs are spherical and in equilibrium. Relaxation of these assumptions results in models that are computationally expensive, often prohibitively so. However, it is possible to dramatically reduce this computational expense by borrowing the technique of Gaussian-process emulation (GPE) from machine learning. Thus, GPE may allow us the use of more general dynamical models. Here we take a first step towards this goal by introducing GPE and demonstrating its use with a toy model, namely a single-component anisotropic Plummer sphere, which we fit to synthetic data drawn from the same model.
Anthony Yeates, Durham
Can we drive coronal evolution models from magnetic maps?
A classic modelling task in Solar Physics is a boundary value problem: how to reconstruct the 3D magnetic field in the Sun’s atmosphere given boundary data on the Sun’s surface? The new generation of magnetic field models are time dependent, but this brings new problems as boundary data for the electric field, rather than just the magnetic field, are required. In this talk, I will present recent work on inverting Faraday’s law: i.e., determining the electric field from observations of only the magnetic field. I will show that L1-minimization provides an elegant solution to this seemingly ill-posed inverse problem.
Lee Kelvin, LJMU
Variation in Galaxy Structure Across the Green Valley
The so-called ‘green valley’ has been of particular interest in recent years as the region in colour-magnitude space populated by galaxies transitioning between the blue cloud and the red sequence (Martin et al. 2007, Wyder et al. 2007). Owing to its relative under-density, the timescale for transition of galaxies across the green valley is thought to be relatively rapid (~1-2 Gyr; Bremer et al. 2018). Multiple mechanisms have been suggested to explain such a transition, from catastrophic major mergers to more passive events such as simply running out of gas. In this talk I present the results of our study into galaxy structure in and around the green valley using a sample of 472 local Universe galaxies in the stellar mass range 10.25 < log M < 10.75. We find a significant surplus of rings and morphological lenses in disk-type galaxies as they transition across the green valley. The existence of such structures rules out violent transformative events as the primary end-of-life evolutionary mechanism, with a more passive scenario the favoured candidate for the majority of galaxies rapidly transitioning across the green valley.
Goran Nilsen, ISIS Neutron and Muon Source,Oxfordshire
The long road to the kagome lattice antiferromagnet: a few materials met along the way…
When geometric frustration – the inability of a magnetic system to satisfy all of its internal interactions – is combined with strong quantum fluctuations, exotic states of matter called spin liquids can result. Beyond being fascinating in their own right, these states have relevance to quantum computing and cryptography, and potentially to high-temperature superconductivity. One of the enduring mysteries in quantum frustrated magnetism is the nature of the spin liquid state in the so-called kagome lattice antiferromagnet, a model which consists of a two-dimensional tiling of corner-sharing metal-ion triangles. Despite significant recent theoretical progress, unequivocal evidence of the predicted states has not yet been observed in experiments. This is partly due to imperfections present in the materials – typically Cu2+-containing minerals – used to study the model. These imperfections include chemical disorder, lattice distortions, and unwanted interactions, all of which conspire to relieve the frustration and generate more conventional magnetic states.
In this talk, I will aim to give an overview of the materials studied as realizations of the kagome lattice antiferromagnet, focusing on two in particular: herbertsmithite (Cu3Zn(OH)6Cl2), volborthite (Cu3V2O7(OH)2.2H2O). I will aim to show how the crystallography and chemistry of these materials lead to the above imperfections, and discuss their implications in each case. Throughout, the main probe used will be neutron scattering. Although the study of kagome lattice materials shows that realizing the intrinsic features of the model is extremely difficult, it also demonstrates the rich variety of physics which emerges in the presence of quantum fluctuations and geometric frustration.
Kenneth Marsh, Cardiff
Point Processes and Dust: Squeezing more information from the observations
The capabilities of the Herschel Space Observatory for dust continuum observations have been far from fully exploited by current analysis techniques. I shall describe an analysis procedure, PPMAP, which can increase by two orders of magnitude the information that can be extracted from such observations, as compared with standard analysis techniques. Rather than produce the standard 2D maps of integrated line-of-sight column density and mean dust temperature, it produces a 4D image hypercube of differential column density as a function of (x,y) sky location, dust temperature, and dust opacity index. This, in turn, allows one to distinguish different environments along the line of sight, which may include very low luminosity protostars detectable via their small amounts of warmer dust, frequently lost in maps of integrated or mean properties. Spatial resolution is enhanced over standard techniques since all input images are used at their native resolution, based on knowledge of the point spread functions, without the necessity to degrade the images to a common spatial resolution. I shall illustrate the power of PPMAP by applying it to Herschel observations of a variety of astrophysical objects, and suggest other possible applications of the technique.
Ricardo Schiavon, LJMU
Chemical Tagging with APOGEE: Discovery of a new old stellar population in the Galactic bulge
I will report the discovery by SDSS-III/APOGEE of a stellar population in the Galactic bulge field, whose abundance patterns resemble those of globular cluster stars. The newly discovered stars are homogeneously distributed across, and kinematically indistinguishable from, the dominant field population. The metallicity distribution of this new stellar population appears to be unimodal, peaking at [Fe/H]•–1, thus being in disagreement with that of the Galactic globular cluster system. I will conclude by discussing the nature of this new stellar population and the possible implications of this discovery for our understanding of the formation of the Milky Way.
Andrew Harrison, Essex
We are going through a paradigm shift in how we view the relationship between microbes and Homo Sapiens. Microbes, acting as pathogens, are responsible for many diseases. But commensual microbes are intimately involved in the regulation of many aspects of our biology and disrupting their regulation can cause disease. Recent technologies such as genome sequencing and growing germ-free animals has led to a step change in discovery and has opened up many avenues for further research.
Meiert Grootes, ESA/ESTEC
Gas-Fuelling in the Group Environment
The accretion of gas onto galaxies (gas-fuelling) is a crucial yet still poorly constrained element determining the star formation history and evolution of a galaxy – particularly in the important environment of galaxy groups. We address this using the Galaxy And Mass Assembly (GAMA) spectroscopic and multi-wavelength survey — using novel, purpose built techniques of morphological classification and radiative transfer modeling of large samples of galaxies to study the impact of the group environment on the gas-fuelling and current star-formation of non-interacting local universe (z < 0.13) spiral galaxies. From this analysis we find that, contrary to the standard paradigm, gas-fuelling of satellite spiral galaxies is on-going, with a rate similar to that found for non-grouped galaxies and almost independent of group halo mass. In fact, modeling indicates that the star formation history of these satellite spirals may be well described by a cycle of quenching and resuscitation of star formation during their satellite lifetime.
Furthermore we explore the implications of our findings for the well known empirical relations of the group environment, e.g. the color density and empirically quantify the group-wide impact of AGN on the star-formation of galaxies in galaxy groups.
Paul Bushby, Newcastle
Magnetic buoyancy instabilities in the solar tachocline
Sunspots are surface manifestations of a large-scale magnetic field that rises to the solar photosphere, under the action of magnetic buoyancy, from deep within the solar interior. It is generally accepted that most of the large-scale magnetic flux that appears at the surface originates from the tachocline, which is a region of strong differential rotation around the base of the solar convection zone. Adopting an idealised model that mimics a local region of the tachocline, I will discuss magnetic buoyancy instabilities in a shear-generated magnetic layer. Recent results suggest that such an instability can only operate in rather restricted regions of parameter space, which would have serious implications for the solar tachocline; I will focus particularly upon the extent to which these results actually constrain the magnetic buoyancy instability in this system. Finally, I will describe some preliminary calculations that suggest that shear-driven magnetic buoyancy may be playing a crucial role in the large-scale solar dynamo (for which there is still no universally accepted model).
Farzana Meru, Cambridge
Spirals, rings, gaps and asymmetries: using disc structure to infer planet formation processes
We have recently entered an era of high resolution, spatially resolved observations of protoplanetary discs, which are revealing exciting disc structures. Such structures give us clues on the protoplanetary disc and planet formation processes. I will discuss some of the causes of spirals, rings, gaps and asymmetries in protoplanetary discs. I will also discuss the possible processes that are causing the spirals in the Elias 2-27 disc, and will show how we might observationally determine if a planet is migrating.
The origin of spirals in galaxies
The mechanism that causes the graceful spiral patterns of galaxies has proven to be subtle and a convincing explanation has begun to emerge only recently. I will describe a recurrent cycle of spiral modes that accounts for the behaviour in simulations, and show that it is consistent with the distribution and kinematics of nearby stars, as recently determined by Gaia.
Coronal Fourier Power Spectra: Implications for Coronal Seismology and Coronal Heating
Fourier power spectra of time-series of coronal emission observed by the Atmospheric Imaging Assembly (AIA) are well described using a power law at lower frequencies that tails to a flat spectrum at higher frequencies, plus a Gaussian-shaped contribution that varies depending on the region studied. This Fourier spectral shape is in contrast to the previously held assumption that coronal time series are well described by the sum of a long timescale background trend plus Gaussian-distributed noise, with some specific locations also showing an oscillatory signal. The implications of the observed spectral shape on the fields of coronal seismology and the automated detection of oscillations in the corona are discussed.
Origin and fate of dust lanes in ETGs
Interstellar material has now been observed in half of early-type galaxies (ETGs). The dust and gas masses span a wide range, supporting scenarios of mergers and accretion as the origin of the ISM. A peculiar class of galaxies stands out: dust-lane early-type galaxies. They make up only four percent of the total ETG population and it is unclear where they should lie in the formation history of galaxies. In this talk I will give an overview of what we know of dusty ETGs as a population and will dig deeper in the history of two very different dust-lane ETGs. Using MUSE observations, spectral modelling and radiative transfer simulations we can unveil clues to the origin and the fate of the dust lanes in these systems.
The Solar Chromosphere
The solar chromosphere is complex, highly structured and dynamic. It is also the layer of the atmosphere in which the transition from optically thick to optically thin radiative losses occurs, the atmosphere moves from being pressure dominated to magnetically dominated. The heating requirements of the chromosphere are far higher than those required to heat the solar corona. This talk will present a basic introduction to the chromosphere and then give a short description of a possible mechanism for heating some of the observed chromospheric features.
CARD: Constraining Progenitor Stars of Type Ib/c Supernovae by Probing the Local HII Environments
Supernova (SN) explosions are the key player in chemical evolution of galaxies because they enrich the interstellar medium with fused heavy elements and trigger new star formation episodes. In order to understand details of SN explosion processes, knowledge of SN progenitor stars is essential. While nature of progenitor stars of Type Ia and Type II SNe is well supported by observational evidence, the nature of progenitor stars of Type Ib/c is still uncertain. Currently, no Type Ib/c progenitor stars have been identified directly. An indirect method to constrain properties of progenitor stars is metallicity analysis of SNe environments. Previous studies, mostly based on small samples drawn from SN catalogues and often using indirect methods for metallicity analysis, have given contrasting results. The talk presents a research project that directly compares local metallicity of HII environments of Type Ib/c SNe with data of Wolf-Rayet stars, deemed as potential Type Ib/c progenitors.SN data are obtained by a spectroscopic survey of SNe HII environments that will produce the most complete survey of SNe environments within 30 Mpc. Ultimate goal of statistical tests of the large SN sample is to substantially strengthen/weaken the assumption of Wolf-Rayet stars as Type Ib/c progenitors.
The deaths of massive stars
A commonly-held view is that stars born with masses above ~8Msun will die as supernovae (SNe) and leave behind a neutron star, whereas stars above some higher mass threshold (~30Msun) will leave behind a black-hole (BH) with little or no SN. However, there have been recent claims that the mass threshold for BH production is much lower (~17Msun). This would have important ramifications for other areas of astrophysics through its influence on the cosmic SN and BH production rates. In this talk I will take a critical look at the evidence for this result, and the outlook for improving its statistical significance.
Understanding the structuring of the solar wind based on coronal magnetic field topology
The acceleration of the solar wind remains one of the most enduring problems in solar system science, the resolution of which is a principal motivation for two major upcoming missions; Parker Solar Probe and Solar Orbiter. The problem is really split into two parts by the observations of two distinct types of solar wind. While it is well established that the fast (and relatively steady) wind emanates from coronal holes, the origin of the slow solar wind (SSW) — and its rapidly varying, filamentary structure — remains a mystery. The strongly fluctuating elemental and ion-charge-state abundances in the SSW suggest that it has some component that originates in the closed corona. I will discuss models of the magnetic topology of the Sun’s atmosphere that suggest that “interchange” magnetic reconnection in the corona may play a key role in the SSW structure.
Euclid: ESA’s dark energy mission – present status and outlook
Euclid, ESA’s second medium class survey mission to explore the dark Universe, was selected in 2011. The mission is optimized for two Dark Energy probes – weak gravitational lensing and galaxy clustering – with a survey area of 15,000 deg2. Meanwhile Euclid passed major development milestones, and is heading towards a launch in 2022. In this seminar the current status of Euclid will be presented. The mission objectives and the driving requirements will be reviewed, with attention to the changes since the mission selection. I will highlight some of the issues encountered during the mission development and the impact on the scientific performances. The scientific community – the Euclid Consortium – is actively involved in a number of initiatives in order to be ready in terms of complementary data collection, predicting scientific performances, and the data processing and analysis methods. Finally, Euclid will not be the only “big science” project addressing Dark Energy – a sketch will be given of the scientific landscape in the next decade.
Space weather and comet interaction with Mars
External drivers like space weather are sources of very intense short-term variability that enhance atmospheric escape, which is currently a major topic in Mars’ exploration. In addition, comets are another source of short intense variability that are believed to have strongly affected the evolution of the terrestrial planets. In 2014, we witnessed the very close flyby of the Oort-cloud comet C/2013 A1 (Siding-Spring) to Mars. This was a unique opportunity to understand how a planetary atmosphere behaves when in direct contact with both the solar wind and a cometary environment. However, before, during and after the comet closest approach, there were significant space weather events which made the interpretation of the observations difficult. In particular, one of the largest Coronal Mass Ejections (CME) of the solar cycle 24 hit Mars about 38 hours before the comet flyby, creating a strong perturbation in the system that, although somewhat diminished over the following hours, was still present during the comet passage.
In this presentation, first, I will describe the Martian plasma system and the space weather context for this cometary encounter, including the propagation of this CME from the Sun till the end of the heliosphere (up to Voyager-2) using data from more than 15 different spacecraft. Then, I will explain the interaction of the comet with the solar wind, and their effects on the shock-accelerated energetic particles that precipitate into Mars’ atmosphere. Finally, I will discuss the comet’s influence on the Martian ionosphere.
Dust properties of nearby galaxies from the JINGLE survey derived using a hierarchical Bayesian approach
The JINGLE (JCMT dust and gas In Nearby Galaxies Legacy Exploration) survey aims to characterize the dust and cold molecular gas properties of nearby galaxies. We developed a method to accurately measure the dust properties of JINGLE galaxies through the fitting of the far-infrared spectral energy distribution (SED). Modified black body functions are the standard method to model far-infrared dust emission in galaxies, but it is known that uncertainties in the photometric data can introduce an artificial anti-correlation between the dust temperature and the emissivity index beta. To overcome this problem and infer reliable dust masses, we apply a hierarchical Bayesian approach and use the information from the parameter distribution of the entire sample of galaxies to better constrain the temperature and beta for each single galaxy. In this way, it is possible to break the temperature-beta degeneracy and obtain a better estimate of the dust parameters.
In my talk I will present the results of applying the hierarchical Bayesian approach to derive dust properties in the JINGLE sample and the scaling relation between dust quantities and other galaxy properties.