External Seminars

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

Dynamical Formation of Compact Object Mergers

Abstract not available

The Emergence of Structure during the Epoch of Reionization

Abstract not available

Magnetised clouds in the Galactic corona: Fuel for future star formation?

The Galactic halo contains a complex ecosystem of multiphase intermediate-velocity and high-velocity gas clouds whose origin has defied clear explanation. They are generally believed to be involved in a Galaxy-wide recycling process, either through an accretion flow or a large-scale fountain flow, or both. In this talk I will present my work on how the magnetic field in the halo affects these processes using magnetohydrodynamic (MHD) simulations. The magnetic field becomes ‘draped’ around the clouds as they move through the halo and this field suppresses hydrodynamic instabilities at the cloud-halo interface. This has widespread implications for gas accretion. The suppression of instabilities prolongs the survival of High-Velocity Clouds (HVCs) so that they are more likely to reach the disk. It also suppresses the mixing of cloud-halo material in the wakes of clouds ejected by the Galactic fountain. This leads to less condensation of cold gas that can be accreted through the fountain process. In addition, the draping of the magnetic field around clouds means that observational constraints on magnetic fields around HVCs can be used to roughly infer their distances. This is useful to constrain their masses and thereby how important they are as a source of accretion.

Title to be confirmed

Abstract not available

Multi-messenger study of the Milky Way with LISA, Gaia and LSST

The upcoming LISA mission is the only experiment that offers the opportunity to study the Milky Way through gravitational wave radiation, exploiting the signals from Galactic double white dwarf (DWD) binaries. I will show that the large number of DWD detections will allow us to use these systems as tracers of the Milky Way potential. Furthermore, in the coming years, a large number of DWDs can be simultaneously detected in both electromagnetic (e.g. with Gaia and LSST ) and gravitational wave radiation. This will provide a unique opportunity to perform a multi-messenger study of the Galaxy. Finally, I will talk about prospects of observing extra-galactic DWDs in the Local Group. I will show that extra-galactic DWDs detectable by LISA are those with the shortest orbital periods and with the highest chirp masses, that are candidates Supernovae Type Ia (SNIa) progenitor, virtually undetectable at those distances in optical. This implies that LISA could be the best instrument able to provide SNIa merger rates across the Local Group.

Searching for the fastest stars in Gaia DR2

The recent second data release (DR2) of the ESA satellite Gaia gives us the first opportunity to search for high velocity stars in the largest stellar catalogue ever produced. Categories of great interest are runaway stars, high velocity halo stars, and hypervelocity stars (HVSs). In this talk I will present our results on the high velocity tail of the velocity distribution of Milky Way stars, using the subset of about 7 million stars with a radial velocity measurement from Gaia DR2 . This study reveals the presence of a population of about 20 unbound stars, half of them with a possible extra-Galactic origin. I will also present ongoing results on the data mining routine we specifically developed to search for the fastest stars, HVSs, in the full (approximately 1.3 billion sources) Gaia DR2 catalogue. Our published estimates show that hundreds to thousands of HVSs are expected to be contained in the full Gaia catalogue, but their identification is not trivial because of the missing radial velocity information, which needs to be obtained with a spectroscopic follow-up. I will conclude presenting HVSs as a powerful probe to map the dark halo of the Milky Way: a population of ~100 Gaia HVSs could be used to nail down the Galactic halo potential parameters with sub-percent precision.