Galaxies, Active Galactic Nuclei and Cosmology

“The Hidden Universe”: linking the evolution of dusty star formation and gas consumption across cosmic time

Kristen Coppin, Jim Geach, Jason Stevens, Maciej Koprowski

Over half of the star formation energy generation in the Universe is extincted at optical wavelengths and enshrouded by dust which absorbs and re-radiates the starlight in the far-infrared/submm; and the 850&450um atmospheric windows allow us to access the redshifted far-infrared emission from this “hidden side” of galaxy formation and evolution.  The James Clerk Maxwell Telescope (JCMT) Cosmology Legacy Survey (S2CLS; Geach et al. 2017) and its extension via the SCUBA-2 COSMOS survey (S2COSMOS; Simpson et al. 2017) and STUDIES (Wang et al. 2017) are the largest and most sensitive and ambitious surveys at 850 and 450 micron (in the submm wavebands) ever conducted.  These unprecedented legacy surveys have yielded thousands of high-redshift galaxies selected in the sub millimetre wavebands - providing an order-of-magnitude improvement in the sample sizes of previous surveys at these wavelengths!

This project will involve making measurements of the submm emission from distant galaxy populations to estimate not only the obscured star formation rate of the galaxies but also the mass of cold gas contained within them fuelling the on-going star formation in a remarkably clean way over a large span of cosmic history. This project will adopt a unique cutting-edge approach, cross-correlating the S2CLS and S2COSMOS and STUDIES2 data with very deep optical/near-infrared galaxy catalogues to explore the evolution of star formation and gas consumption across cosmic time and comparing the results to state-of-the-art models, such as EAGLE.  A key theme will thus include measuring the evolution of the ISM mass over redshift and how this depends on galaxy properties such as mass and environment, as well as other galaxy properties like AGN activity. We are involved in ongoing efforts to perform detailed follow-up of these high-z submm-detected sources at higher resolution with the Atacama Large Millimetre Array (ALMA) situated at 5000m on the Chajnantor plateau in Chile, and the findings of this work will feed into new ALMA telescope proposals.  There will also be an opportunity to travel to the JCMT in Hawaii to help out with observing campaigns for related submm science led by astronomers in this supervisory team.

Cosmic Chemical Enrichment from the First Stars

Chiaki Kobayashi, Fiorenzo Vincenzo

The student will study cosmic chemical enrichment using computational simulations. Our simulation code self-consistently includes relevant physics of atomic matter - hydrodynamics, star formation, chemical enrichment from Type II and Ia supernovae, and feedback from supernovae and supermassive black holes - and therefore, the predictions are comparable with observations from nearby to distant galaxies. In the early Universe, the first stars are supposed be more massive and cause pair-instability supernovae or black-hole-forming faint supernovae, and thus have different nucleosynthesis yields. The student will include the chemical enrichment from the first stars into the simulation code, and constrain the nature of the first stars by comparing to the observations of high-redshift galaxies (and quasar absorption line systems).

High sensitivity, high resolution imaging at radio wavelengths of four nearby galaxies

Elias Brinks, Luke Hindson

Modern radio telescopes, such as the Very Large Array (VLA) in New Mexico, are revolutionising our understanding of galaxies. Radio emission, rather than picking up emission from stars like at optical wavelengths, instead probes material floating between the stars, the interstellar medium (ISM). This is where on the one hand processes leading to the formation of new generations of stars take place (the cooling and collapse of neutral gas clouds leading to molecular clouds which fragment and collapse further to form stars) and on the other stars exploding as supernovae return matter and relativistic electrons (also known as cosmic ray electrons) to the ISM.

Radio emission is turning out to be a powerful probe for both the formation of new generations of stars, through tracing the thermal emission generated in HII regions, and the death throes of stars, by mapping the relativistic electrons produced in supernova shocks, which lose their energy as they spiral around magnetic field lines, generating non-thermal synchrotron radiation. Unlike optical observations, radio emission is hardly affected by dust which gives radio studies the potential to map star formation out to large redshift. Eventually that will be one of the key areas of research for the Square Kilometre Array, an ambitious “World” telescope, the first phase of construction of which is imminent.

A substantial allocation of observing time was awarded to observe 4 nearby galaxies with the VLA in great detail covering several wavelength and mapping total intensity as well as full polarisation. Observations have started in Sept 2016 and will continue through 2017. Improvements in telescope receivers in recent years means our study will be vastly superior to what has been achieved thus far. The data will enable many different studies. A challenging, but rewarding project that is foreseen is to derive total and polarised intensity maps to derive the total (equipartition) strength of the magnetic field, and the constituent ordered and turbulent fractions. We will also exploit the near contiguous coverage across frequency to apply Faraday Rotation-Measure (RM) Synthesis. We will use the Faraday rotation measure, its azimuthal variation, and RM–Synthesis to obtain a census of axisymmetric mean magnetic field strength and magnetic pitch angle, all crucial for testing the theory of a galactic dynamo.

Understanding the bright, high-redshift tail of the submillimetre galaxy population

Jim Geach

When we observe the Universe in visible light, we only see part of the picture. Much of the visible light in the Universe is blocked out by interstellar dust, which obscures starlight, and this can be particularly excessive for distant galaxies undergoing a phase of intense growth. We need to understand these galaxies to get a proper understanding of how galaxies form and evolve. By observing light in the submillimeter part of the spectrum, we can actually see the dust itself, because it glows at these wavelengths. This allows us to pin-point dusty, distant, active galaxies that would otherwise be missed. Importantly,  we are able to detect galaxies out to far greater distances than is typically possible with traditional visible-light surveys.

This project will involve taking a major responsibility in a submillimeter sky survey that is the largest of its kind to date: the SCUBA-2 Large eXtragalactic Survey (PI: Geach) with a goal to detect the rarest - brightest and most distant - submillimeter galaxies known. Because these galaxies are relatively rare, they are not detected in large numbers in existing submillimeter surveys. This new survey will rectify that, providing the largest sample of such galaxies to date. The student will help conduct observations, lead data reduction and produce the first catalogues from the survey. These will be used to determine the properties of the brightest, most distant submillimetre galaxies, focusing on the abundance of such systems, their individual properties and how they can be explained in terms of the latest cosmological models of galaxy formation.

The WEAVE-LOFAR view of star forming galaxies

Dan Smith

This project will lead key parts of the analysis and scientific exploitation of the international WEAVE-LOFAR survey, which is a cornerstone of the science plans for the new WEAVE spectrograph. WEAVE-LOFAR (which is led by Dan Smith) will initially spend five years obtaining more than a million optical spectra of sources selected at low radio frequencies, and this information is essential for unlocking the immense power of the new LOFAR observatory for studying star-forming galaxies at all redshifts, and far beyond detection with SCUBA-2 or Herschel.

As well as helping to build a unique legacy of high-quality, uniform radio source spectra, this project will play a crucial role in extracting early science results from the WEAVE-LOFAR data set. There are a very wide range of possible questions that can be addressed with these data, including dust-free determinations of how star formation in galaxies is affected by stellar mass and environment, and how this evolves with redshift. The project will be driven by the student with flexibility to choose the direction according to his/her interests.

Do we understand galaxies, really?

Dan Smith, Jim Geach, Chris Hayward (Simons Foundation, USA)

Astronomy is unlike many other sciences since we are unable to frame observational experiments; our view of the dynamic processes shaping galaxies is fixed in both direction and time (at least on human timescales). The best way to circumvent these potentially crippling issues is through using state-of-the-art simulations, built using realistic astrophysics. These simulations are now sufficiently advanced that we can study them using the same observational tools that we use for analysing real galaxies, providing an unique insight on what our observations are really able to tell us about their (and ultimately, our) place in the cosmos. The student will lead the effort to confront some of the latest galaxy modelling tools (including panchromatic SED fitting techniques) with the simulations, and publicise the results of this analysis worldwide. The successful applicant will also have the opportunity for extended visits to collaborate with the team that built the simulations (led by Dr Chris Hayward in New York City).