Institute for Astronomy

Milky Way & Local Group PhD Projects

Research projects on offer in our Milky Way & Local Group Galaxies research group:

Probing the Milky Way stellar and dark matter haloes with DESI spectroscopy

Supervisor: Sergey Koposov

 

In the last 15 years we realised that the Milky Way stellar halo is a real treasure trove of information about the galaxy formation and evolution because it is believed to have formed through hierarchical accretion of multiple dwarf galaxies and star clusters onto the Milky Way. 

A major leap in the studies of the Galactic stellar halo after the arrival of digital sky surveys such as Sloan Digital Sky Survey 20 years ago is happening now with the arrival of data from the Gaia satellite that provides us with proper motions and distances of billions of stars throughout the Galaxy. These data have already provided major revelations that the Milky Way had a massive merger with a galaxy labelled Gaia-Enceladus several billions years ago and that the stars from that galaxy are now dominating the stellar population of Milky Way outskirts. 

While the ongoing Gaia mission is revolutionary, another window into the Milky Way halo is about to open - the spectroscopic surveys that will measure spectra of millions of stars. These spectra will provide chemical abundances and radial velocities complementing existing datasets to create a 7-dimensional map of the Galaxy. One of the earliest spectroscopic surveys to start is the DESI spectroscopic survey that had its first light this spring.

A student is invited to lead the study of the kinematics and chemistry of distant stars in the Milky Way halo using the data from DESI survey in combination with data from Gaia. That work will involve analyses of large datasets, statistical modeling and visualisation. The key directions of research will be (i) detecting and characterizing stellar substructures in the Milky Way halo, (ii) measuring the velocity distribution of the smooth halo out to large distances to characterize dark matter mass distribution in the Milky Way.

Experience with Python is highly recommended.

The student will work with Sergey Koposov, his collaborators in Edinburgh and Cambridge University as well as the DESI Milky Way survey working group.

Dark Matter in the Milky Way and the LMC

Supervisors: Jorge Peñarrubia & Michael Petersen 

Video: Dark Matter in the Milky Way and the LMC
Dark Matter in the Milky Way and the LMC

The Milky Way is the only system of the Universe where we can measure the full motion of stars, and thus derive unique constraints on the amount and distribution of Dark Matter on galactic scales. To do so, astronomers typically model the orbits of stars in a Galactic potential that is typically assumed to be in dynamical equilibrium. This assumption has recently proven to be wrong. The brightest satellite galaxy (Large Magallanic Cloud, or LMC) appears to be falling into our Galaxy for the first time embedded in a massive dark matter halo, which is expected to cause strong disequilibrium features in the Galaxy potential.

The goal of this project is to construct state-of-the-art numerical models that follow the dynamical interplay between the LMC and the MW. In particular, the project will investigate the distribution and amount of dark matter in both systems, making use of powerful inference techniques for comparison with Gaia satellite data (currently measuring the distances and velocity vectors for ~109 stars across the entire galaxy). The student can expect to place constraints on the distributions of dark matter for both the MW and LMC as a first step, followed by the construction of more advanced models geared at identifying dynamical effects of the LMC on the Galactic disc and stellar halo, as well as the tidal deformation of the LMC as it falls into the Milky Way.

The student taking on this project will gain a deep knowledge of N-body techniques, Bayesian tools of inference, and data analysis. Previous experience with programming (e.g. Python) and dynamical (e.g. N-body) tools  would be very helpful, but by no means mandatory.

Chaos in the Universe

Simon Portegies Zwart & Anna Lisa Varri

Video: Chaos in the Universe
Chaos in the Universe

Stars move with respect to each other due to the Newtonian forces between them. The corresponding equations of motion are intrinsically chaotic.  As a consequence, computers have great difficulty solving them, except if we design special algorithms to address this particular issue. Once these algorithms are in place, we can study the key physical processes that shape the evolution of collisional stellar systems.

One outstanding problem we intend to address is the nexus between phase space statistical behavior and chaos.  But these problems are also associated with the transport of energy and angular momentum within the system, and with the growth of entropy.  The latter aspect relates the evolution of the phase space distribution function to the arrow of time. These are fundamental concepts that link applied mathematics, theoretical physics and computer science directly to astronomy.

Understanding the evolution of the phase space structure of collisional stellar systems can, therefore, lead to new insights into the formation of binary stars in dense star clusters, the production of black holes of different classes of mass, and the appearance of tidal streams in the Galaxy.

From an observational point of view, these topics can aid our interpretation of stellar-mass black hole merger detections with LIGO/VIRGO, their radio and X-ray counterpart observations, and the exquisite astrometric measurements currently delivered by the Gaia satellite.

This PhD project is a joint Leiden-Edinburgh PhD project, proposed to be carried out under the joint supervision of Simon Portegies Zwart and Anna Lisa Varri, ideally with an equal share of time spent in Leiden and Edinburgh.

 

Galaxy Archaeology with Asymptotic Giant Branch Stars

Annette Ferguson and Olivia Jones

Thermally-pulsing asymptotic giant branch (TP-AGB) stars are the descendants of low-to-intermediate mass (~1-8 solar masses) main-sequence stars. Their numbers reflect  the star formation histories of galaxies over the last few billion years and their chemical properties constrain the metal enrichment of galaxies as well as their  dust production rates.   Compared to other resolved stellar population tracers (e.g. main sequence stars, red giant branch stars), AGB stars offer some tremendous advantages --  their high luminosities at near and mid-IR wavelengths make them detectable out to ~10-20 Mpc distances while the fact that their spectral energy distributions peak at long wavelengths makes them much less susceptible to dust extinction.

We are about to enter a golden age for AGB studies in Local Volume galaxies. The launch of JWST in 2021, and Euclid in 2022,  is expected to lead to many breakthroughs in our understanding of this enigmatic phase of stellar evolution and how we can use AGB populations to quantitatively constrain galaxy histories.   We seek a PhD student to work with us one or more of the following projects:

  • Analysis of deep pointed observations of nearby dwarf galaxies (NGC6822, IZw18) with JWST GTO data, quantifying their AGB populations and dust production rates
  • Preparing for and conducting a census of AGB stars in tens to hundreds of nearby galaxies with deep wide-field survey data from Euclid
  • Exploit  various existing and forthcoming datasets to improve calibration of AGB stellar models and build a robust methodology to use AGB stars as quantitative star formation history tracers.

 

Quantifying Photon Dominated Regions with ALMA & JWST

Pamela Klaassen

Video: Quantifying Photon Dominated Regions with ALMA and JWST
Quantifying Photon Dominated Regions with ALMA and JWST

Photodissociation Regions (or PDRs) are the interface between the hot, ionised gas surrounding a massive star and its cooler, molecular surroundings.  The shock physics and chemistry in these PDRs are so dynamic that it’s hard to figure out where to start understanding them. PDR models are still quite primitive because we haven’t had access to high resolution observations  (spatial *and* spectral) at the relevant wavelength ranges (IR to sub-mm) where the interesting shock chemistry happens (which traces the physics).

In this project, the student will apply for and then lead an ALMA project to quantify the PDR and molecular gas in the Horsehead nebula. This region has been chosen because  the ALMA project can act as a good compliment to the 

JWST/MIRI Guaranteed time project observing the same target which the student will participate in.

The VLT-MOONS Galactic survey: towards a complete chemo-dynamical characterisation inner bulge and bar

Oscar A. Gonzalez

 

The understanding of galaxy formation and evolution is one of the fundamental goals of modern astronomical research. The Milky Way offers a one-of-a-kind opportunity to investigate the formation of a prototypical disc galaxy by looking at the individual ages, chemical abundances, and orbital movements of its stars. In recent years, we have witnessed remarkable progress towards characterising the stellar populations of the Milky Way thanks to large-scale spectroscopic surveys. However, the innermost regions of the Galaxy have remained mostly unreachable to them due to the very large amounts of dust obscuration. This presents a tremendous limitation, as simulations show us that the properties of the central, in-plane regions of disc galaxies hold unique fingerprints of the role that different processes such as dynamical instabilities, hierarchical merging, and dissipative collapse played across the history of the entire galaxy.

In this project, the student will join the leading team of the VLT-MOONS Galactic Survey. The student will work on the development of tools to derive radial velocities, stellar parameters and abundances for millions of stars to be observed with MOONS during its lifetime. The student will participate closely on the design and preparation of the survey, the analysis of commissioning data, science verification, and have a leading role in the analysis the first year of the GTO survey observations. A fraction of the time can be dedicated to the analysis of state-of-the-art simulations of bulge formation and VLT-MUSE observations of nearby bulges, in order to place the forthcoming MOONS results in a general context of bulge formation.

Hubble's legacy in the Magellanic Clouds

Chris Evans

With masses more than ten times that of the Sun, these stars burn very brightly for just a few million years before exploding violently as supernovae. During their lives they manufacture the materials from which planets and life are made and, via their high- energy winds and explosive deaths, they shape the chemistry and evolution of their host galaxies. Only by learning how these stars behave in the local Universe can we attempt to interpret distant, star-forming galaxies, whose light is dominated by vast numbers of these spectacular objects, and which astronomers use to chart the history of the Universe from the Big Bang through to the present.

The Hubble Space Telescope is now taking observations for the unprecedented 1000-orbit ULLYSES program to build an ultraviolet spectroscopic library of massive stars while the telescope is still functioning. The targets build substantially on optical data from projects led in the past by Evans. This project will combine these existing data with new observations from an X-Shooter Large Programme and the new UV data from HST. Initial topics for study will be the UV morphological properties of the ULLYSES targest in the spectacular 30 Doradus star-forming region, quantitative analysis of the terminal velocities of their stellar winds, and seeking new insights into binary systems where the properties of the secondary have eluded us from optical spectroscopy alone.

Under the Astronomical Instrumentation PhD projects see also:

  • Resolved Stellar Populations with ELT-HARMONI: setting the path from the VLT to the ELT Oscar A. Gonzalez