Centre for Extragalactic Astronomy

Research in Observational Astronomy

This page describes a selection of our current observational research projects. Additional information on these projects and others being undertaken by researchers at Durham can be found through their personal home pages:

  • AGN and compact-source accretion:
    • AGN and the growth of galaxies Active Galactic Nuclei (AGN), the sites of growing black holes (BHs), are no longer viewed as rare “exotic” phenomena but are seen as central players in galaxy formation and evolution. Our research aims to advance understanding of the evolution of AGN, the connection between AGN activity and star formation, and the role of AGN in galaxy formation and evolution.
    • The brightest high mass X-ray binaries and the Eddington threshold The radiative and mechanical output of X-ray binaries in star forming galaxies is dominated by the brightest objects, which are likely to have been present in large numbers in the early Universe and so will have contributed to feedback. However, the accretion physics in this Eddington threshold regime (log Lx ~ 38 - 39.5) is relatively poorly constrained by observations, particularly at X-ray energies below 3 keV. We are addressing this with new systematic studies of X-ray binaries in our own Galaxy and other nearby systems, and will use this to predict the impact of X-ray binary feedback at high redshift.
    • Accreting white dwarfs as accretion disk laboratories Accretion is the process that drives and regulates the growth of most objects in the Universe, yet the physics and dynamics of accretion is still poorly understood. Due to their relative simplicity compared to other accretor types, accreting white dwarfs provide a unique laboratory to study and understand the physics of accretion under different environments. We are using TESS observations of hundreds of accreting white dwarf systems to systematically study the brightness variations arising from mass transfer rate changes through accretion disks under different environments. Our results are used to test current theories of accretion disks, and used to test whether the physics of accretion can be considered scale-invariant across different accretor types (e.g young stellar-objects, neutron stars, black holes) of different mass, size and accretion rate.
    • Radio surveys as a key to understanding AGN feedback The advent of next-generation of low-frequency radio telescopes offers a novel way to determine the processes by which AGN can influence their host galaxies' evolution. Our research focuses on using unique sub-arcsecond radio imaging techinques to understand the origin of radio emission in both radio-quiet and radio-loud AGN, with targeted observations and a Northern sky survey using the Low Frequency Array.

  • Galaxy formation and evolution:
    • Probing galaxy halos with strong absorption line systems Galaxies are part of a complex cosmic ecosystem in which gas is continuously exchanged between the inner regions where stars form and the diffuse intergalactic medium that pervades the universe. By combining observations from the world largest telescopes, we are studying strong absorption line systems within galaxy halos to obtain a comprehensive view of how galaxies acquire the fresh fuel needed for the formation of stars, and how they disperse back into the cosmos gas that is enriched with heavy elements. Find out more on the IMAGE group pages.
    • The KMOS Galaxy Evolution Survey (KGES) The peak in the volume averaged star-formation rate in galaxies occurs in the redshift range z~1-2. At this epoch, the star formation rate in typical galaxies was a factor ~20x higher than in the local Universe. This is the era when most of the stars (and also black holes) in the Universe were formed. The observational task is to address "how" and "why” galaxies at this epoch were so much more efficient at forming stars than in galaxies today, and which physical processes were responsible for “crystallising” the Hubble sequence below z~1. We are therefore undertaking a spatially-resolved study of ~2000 star-forming galaxies at z~0.5–2 to constrain how which dominant processes assembled the bulk of the stellar mass in today’s massive galaxies. This survey is underpinned by our KMOS Guaranteed Time (GT) observations and also exploits our MUSE, SINFONI, ALMA and NOEMA programs.
    • Ultraluminous dust-obscured galaxies: This phase of galaxy formation plays an important role in the growth of massive galaxies in the early Universe. To understand it, we are pursuing a range of wide-field sub-mm surveys using single-dish facilities and detailed interferometric studies with ALMA to investigate the physical processes which drive the extreme activity seen in these systems.
    • The first four billion years We are undertaking an observational program that exploits gravitational lensing by massive clusters to identify and study properties of the first galaxies that formed in the Universe. Our goal is to understand how the first galaxies reionised the intergalactic medium around a redshift of z~8 and the first galaxies then settle in to ordered rotating disks. This program exploits observations with KMOS (in particular using Durham guarenteed time), MUSE and ALMA.
    • Star formation and galaxy evolution in the nearby, resolved Universe The life cycle of gas, stars, and dust in star-forming galaxies is very complex. While we qualitatively understand the physical processes involved in governing the galactic gas recycle, we still do not have a clear quantitative description of them. In particular, the role of massive stars in regulating star formation and galaxy evolution remains a crucial observationally unconstrained component. With so-called integral field units like the famous MUSE instrument on the Very Large Telescope we target star-forming regions in the Milky Way and nearby galaxies to derive an observational quantification of the effects of massive stars on how galaxies form stars and evolve.

  • Galaxy groups, clusters, and large-scale structure:
    • AGN feedback in clusters: The formation of the most massive galaxies appears to be influenced by the nuclear activity at its core. These massive galaxies also host the most massive black holes and gas that accretes into it fuels very energetic outflows and relativistic jets. Studies of this outflow close to the black hole, within the galaxy and out into the gas that surrounds it help constrain the energetics of these systems.
    • Cluster starbursts Massive galaxy clusters in the local Universe are devoid of strongly star-forming galaxies, but as we survey clusters at higher and higher redshifts we see an increasing level of star-formation activity in their core regions. We are using new multiwavelength surveys to understand the environmental processes which drive the strong evolution in star-forming galaxies in dense environments.
    • Uncovering ensembles of Milky-Way analogues with PAUS: Key tests of the standard Cold Dark Matter structure formation model, from "the missing satellite problem" to "the too big to fail problem", rely on the assumption that the Milky-Way and Andromeda systems are statistically representative of ~1012 M_⊙ halos. This project proposes to test this assumption by measuring accurately the galaxy content of groups down to Milky-Way halo masses using the novel "Physics of the Accelerating Universe Survey" (PAUS) sampling all large scale environments in which such halos reside.

  • Milky way and local galaxies:
    • The Milky Way mass to 10% precision The total mass of the Milky Way is a fundamental - yet poorly constrained - astrophysical parameter. We are aiming to measure the total mass of the Milky Way, to better than 10 percent precision, using 6D phase-space measurements of halo stars out to 250 kpc.
    • The Stellar Initial Mass Function in Giant Elliptical Galaxies The stellar initial mass function (IMF) is fundamental in controlling the properties of galaxies, in particular their mass-to-light ratios. Whether the IMF is universal, or depends on galaxy type, mass or formation history, is hotly debated. We are using novel observational methods to discover low-redshift strong-lensing galaxies, and exploiting robust stellar masses derived from these lenses to test for non-universality of the IMF in elliptical galaxies.
    • Construction and Exploitation of new FP-based peculiar velocity surveys While redshift surveys are used extensively to map the local cosmography additional information can be derived from peculiar velocities, i.e. the motions that galaxies (and galaxy clusters) have in addition to the Hubble expansion. Peculiar velocities (vpec) arise from inhomogeneities in the large-scale mass distribution and can be determined by accurate distance measurements (D), via vpec≈ cz − H0 × D, where cz is the redshift and H0 is the Hubble constant.

  • Cosmology and dark matter:
    • Big Bang Nucleosynthesis A few minutes after the Big Bang, there was a brief period of time where the first elements were made - primarily the isotopes of hydrogen and helium, together with trace amounts of the other light elements. By measuring the relative production of each isotope that was made during this time, we can learn about the Universe just moments after the Big Bang.
    • Cherenkov Telescope Array Studies of Dark Matter and AGN High energy astrophysical phenomena are key to understanding particle acceleration and annihilation processes in the Universe, and may also provide new insights into the nature of dark matter (DM). One of the key instruments to meet this challenge will be the Cherenkov Telescope Aarry (CTA). We are using current instruments, such as Fermi, and theoretical calculations to work on testable predictions for CTA.
    • Dark matter particle colliders: In terrestrial collider experiments such as the LHC, the masses and interaction strengths of Standard Model particles are measured by smashing them together, and watching the trajectory of the resulting debris. Dark matter cannot be accelerated around Geneva, but it is injected into natural colliders such as the Bullet Cluster in sufficient quantities for its trajectory to be mapped via gravitational lensing.
    • Imaging Surveys for Cosmology Among the best observational tools for studying the dark energy equation of state are surveys designed to measure the large-scale structure of the Universe. Durham has a long history of performing surveys of luminous red galaxies, galaxy clusters and quasars and then using these surveys to test cosmological models over a wide redshift range. Currently we are leading a new generation of optical and infrared photometric surveys to extend these cosmological studies up to z~1 for galaxy clusters and z>3 for quasars.
Durham Surveys and Networks: - Durham is involved in various networks and surveys: