Hugh Garsden's Work Page
I work at The University of Manchester, Jodrell Bank Centre for Astrophysics, in Phil Bull's group, and am part of the worldwide Hydrogen Epoch of Reionization Array project (HERA). HERA is next-generation radio telescope situated in South Africa that has a good chance of detecting the 21cm signal from neutral hydrogen in the early Universe. Such a detection is going to tell us a lot about what happened in those early times. A tentative detection has made of the global (sky-averaged) signal (Bowman) but interferometers like HERA will tell has how that signal is distributed (its "clumpiness"), which provides information on large scale structure evolution (like galaxies).The most important innovation in HERA is its built-in redundancy. It makes multiple observations in parallel which can be combined to smooth out variations due to hardware noise and variability.
I am working on:
- Very large computer simulations of HERA
observations
- Using large computer clusters
- Using GPUs
- Writing software for simulations
- Validation of simulations
- Modelling the parameters (and their errors) that affect HERA observations
- Using Bayesian/MCMC and other techniques/statistics
- Applying very large simulations to push up the number of parameters we can model, way beyond what is usually achievable.
- Novel calibration methods
- 21cm power spectra from HERA observations
- Software and software pipelines
- Methods for removing artifacts and systematics
- Power spectrum analysis
- Issues that may affect the redundancy in the HERA telescope
- Some variability may be harder to smooth out,
e.g. antenna beam differences
- Identifying these will allow them to be tightened up in future
The effect of dish beam variability on calibration. A paper on that work.
Previous position
From 2020-2022 I worked at Queen Mary University of London on the same project.
From 2014-2019 was at the Harvard-Smithsonian
Center for Astrophysics within Lincoln Greenhill's LEDA
(Large-aperture Experiment to detect the Dark Age) project, on
several astrophysics projects using data from the OVRO-LWA
radio telescope in California. My work covered:
- 21cm cosmology at Cosmic Dawn/EoR
- Observations of the global HI signal
- Observations and power spectra
- Pulsar observations
- Radio interferometry
- Data processing
- Data analysis
- Telescope management
Most of my work was on generating a 21 cm power spectrum from OVRO-LWA data using the delay spectrum method. This generates a 2-D cylindrical power spectrum of observations at low radio frequencies, where the foregrounds (galxies etc. and any we want to separate from the 21cm signal) are isolated into a wedge in the power spectrum. We have successfully produced power spectra at a frequency of 48 MHz (the highest redshift power spectrum so far!) and you can view my paper on this work. We also ran of simulations of the sensitivity of the OVRO)-LWA telescope for making a 21 cm detection, and the results are promising.
I also worked on 21cm global signal cosmology. The LEDA group is one of a few around the world following up the global signal detection reported by Bowman.
We have gathered several hundred hours of sky spectra and are analysing that using
a pipeline developed by Danny Price. We have obtained spectral indices of the sky from that work which is also being published.
I have also made some observations of pulsars through the Sun's corona. LEDA had a project to measure the magnetic field close to the sun, but we were beaten to it by some of our collaborators. It did spur the development of a new software pipeline system combining CPUs and GPUs -> "Bifrost". A paper was published on that (in my ref list below) and it has a life of its own now.
Previous position
From 2012-2014 I was at
CEA, south of Paris, in the CosmoStat
Laboratory. I was employed by the Université-Paris-Diderot.
I implemented compressed
sensing for radio astronomy imaging in the LOFAR
Radio Telescope, the first (I believe) implementation
of compressed sensing in a working telescope imager.
I was a member of the LOFAR
Slow Transients Software Team and the LOFAR Source
Finder Working Group. Finding "slow" transients involves
searching radio images for astronomical sources and
comparing them against known sources. This has to be done
in an automated way using software, due to the huge number
of images generated. I worked mainly on source finding,
software and testing.
PhD
I worked on gravitational microlensing and built the first microlensing software simulator that could incorporate 1 billion microlenses. Using this I published several papers studying lensing in this new region of parameter space.Previous lives
Prior to getting my PhD I worked as a software engineer in industry and at universities in research groups in physics, computing, speech synthesis, and biomedicine.Education
- PhD, University of Sydney. Gravitational lensing, numerical computing, and supercomputer simulations.
- B.Sc. (Hons I), University of Adelaide and University of Queensland. Physics, Maths, Computing.
Research Interests
- 21cm cosmology
- Numerical computing, algorithms, parallel computing, GPUs, deep learning, tensor flow
- Cosmology
- Simulations in these fields
- Radio astronomy, interferometry, algorithms
- Pulsars
- FRBs
- Transients
- Multi-messenger astronomy
- Gravitational lensing
- Quasars
- Supercomputing, Big Data
- Signal and image processing
Presentations
A representative sample:- 21 cm cosmology and power spectra, CSIRO, Sydney, Australia, 2017.
- Compressed sensing, SKA Radio Transients Meeting, Kruger Park, South Africa, July 2013.
- Testing Source Finders with Simulated Maps. LOFAR Transients Meeting, Amsterdam, Dec 2012
- High Resolution Numerical Analysis of Quasar Microlensing. Institute of Astronomy, Cambridge, U.K., Dec 2010
Publications
Please view my list on SAO/NASA ADS.plus 14 papers from my previous lives.