Detecting the Epoch of Reionisation with the Murchison Widefield Array
One of the primary science experiments for the Murchison Widefield Array (MWA), and the future Square Kilometre Array (SKA-Low) telescope, is detection of the neutral hydrogen signature from the first billion years of the Universe, and exploration of the growth and evolution of the first stars and galaxies. This period is termed the Epoch of Reionisation (EoR). This exceptionally weak signal is buried within contaminating signals from other Galactic and extragalactic radio sources, and thermal noise of the instrument itself, making this a technically challenging problem, on par with the quest to detect gravitational waves.
Area of science
Astronomy
Systems used
Magnus, Galaxy and Zeus
Applications used
Python, C, MWA_ToolsThe Challenge
A key tracer of the EoR is the spectral line of neutral hydrogen. Observation and analysis of this spectral line provides detailed information about the state of the intergalactic medium at early times, and the spatial and temporal structure of the reionisation of hydrogen. Due to the expansion of the Universe, the emission line, with an emitted wavelength of 21 cm, is observed at longer wavelengths (lower frequency) the more distant its emission. Neutral hydrogen from 12 billion years ago is observable today at low radio frequencies, with the signal expected in the 100-180 MHz range. This is accessible with new large-scale radio instruments such as the Murchison Widefield Array (MWA), a low-frequency radio telescope in the Western Australian desert. The MWA’s primary science goal, and a key priority for the future Square Kilometre Array (SKA), is measurement of the EoR signal. The remote location is crucial for providing the radio quietness required to detect this weak signal; digital TV, FM radio and other transmitters all use these same frequencies, and the remoteness of the Murchison region gives Australia a distinct advantage to explore this early Epoch compared with other locations in the world.
The Solution
Acquiring terabytes of low-frequency radio data is key to accessing this early epoch of the Universe. The weak hydrogen signal needs to be observed for several hundred hours in one patch of sky to reduce the noise to below the signal level. This presents a challenge in terms of data volume, as well as having the algorithms and computing available to sift through the data efficiently.
The Outcomes
The MWA EoR group has been acquiring and processing data with Pawsey resources for the past five years, with published upper limits on the signal strength stemming from these data. With the raw data located at the Pawsey Supercomputing Centre, and algorithms and software developed, test, implemented and producing science results on Pawsey resources, we aim to expand our data processing towards an MWA detection of this crucial period in the history of the Universe.
The physical co-location of the data stored at Pawsey, and the supercomputing infrastructure, are key ingredients to be able to prosecute this science case without large data transfer. It also allows us to sift through the same data multiple times as our methods and analysis improve.
List of Publications from this project
1. Trott, C.~M., and 35 colleagues 2020., “Deep multiredshift limits on Epoch of Reionization 21 cm power spectra from four seasons of Murchison Widefield Array observations”, Monthly Notices of the Royal Astronomical Society 493, 4711.
2. Nasirudin, A., Murray, S., Trott, C., Greig, B., Joseph, R., Power, C.\ 2020.\ The Impact of Realistic Foreground and Instrument Models on 21cm Epoch of Reionization Experiments.\ arXiv e-prints arXiv:2003.08552.
3. Watkinson, C.~A., Trott, C.~M., Hothi, I.\ 2020.\ The bispectrum and 21cm foregrounds during the Epoch of Reionization.\ arXiv e-prints arXiv:2002.05992.
4. Beardsley, A.~P., and 58 colleagues (3rd author) 2020.\ Science with the Murchison Widefield Array: Phase I results and Phase II opportunities – Corrigendum.\ Publications of the Astronomical Society of Australia 37, e014.
5. Li, W., and 46 colleagues 2019.\ First Season MWA Phase II Epoch of Reionization Power Spectrum Results at Redshift 7.\ The Astrophysical Journal 887, 141.
6. Barry, N., and 29 colleagues 2019.\ Improving the Epoch of Reionization Power Spectrum Results from Murchison Widefield Array Season 1 Observations.\ The Astrophysical Journal 884, 1.
7. Jordan, C., Trott, C., Lynch, C., Line, J.~L.~B.\ 2019.\ Probing the Epoch or Reionisation with the MWA.\ Quest for the Origin of Particles and the Universe (KMI2019). The 4th KMI International Symposium. 18-20 18.
8. Trott, C. M., Fu, S.-C., Murray, S, Jordan C.H., et al. “Robust statistics toward detection of the 21~cm signal from the Epoch of Reionisation”, 2019, MNRAS, in press
9. Trott C. M., Watkinson C, Jordan CH, Yoshiura S, Majumdar S, et al. “Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array”, 2019, PASA, in press
10. Line, J. L. B.; McKinley, B.; Rasti, et al. Trott, C. M. (15 authors), “In situ measurement of MWA primary beam variation using ORBCOMM”, 2018, PASA, 35
11. McKinley, B.; Bernardi, G.; Trott, C. M.; Line, J. L. B.; Wayth, R. B.; Offringa, A. R.; Pindor, B.; Jordan, C. H.; Sokolowski, M.; Tingay, S. J.; Lenc, E.; Hurley-Walker, N.; Bowman, J. D.; Briggs, F.; Webster, R. L., “Measuring the global 21-cm signal with the MWA-I: improved measurements of the Galactic synchrotron background using lunar occultation”, 2018, MNRAS, 481(4), 5034-5045
12. Trott, C M.; Jordan, C. H.; Murray, S. G.; et al (20 authors), “Assessment of Ionospheric Activity Tolerances for Epoch of Reionization Science with the Murchison Widefield Array”, 2018, ApJ, 867(1), 15
13. Li, W.; Pober, J. C.; Hazelton, B. J.; Barry, N., et al., Trott C.M. (25 authors), “Comparing Redundant and Sky-model-based Interferometric Calibration: A First Look with Phase II of the MWA”, 2018, ApJ, 863(2), 170
14. Murray, S. G.; Trott, C. M.; Jordan, C. H., “A Clustered Extragalactic Foreground Model for the EoR”, 2018, Proceedings of the International Astronomical Union, IAU Symposium, Volume 333, pp. 199-202
15. Procopio P, Wayth R, Line J, Trott CM, Intema H, Tingay SJ, 2017, “A high resolution foreground model for the MWA EoR1 field: model and implications for EoR power spectrum analysis”, PASA
16. Jordan CH, Murray S, Trott CM, Wayth RB, Mitchell DA, Pindor B, Procopio P, Morgan J, 2017, “Characterisation of the ionosphere above the Murchison Radioastronomy Observatory using the Murchison Widefield Array”, MNRAS
17. Line, J.L.B., Webster, R.L., Pindor, B., Mitchell, D.A., Trott, C.M., 2016, “PUMA: The Positional Update and Matching Algorithm”, PASA, 34 ,3
18. Beardsley, A.P., Hazelton, B.J., Sullivan, I.S., Carroll, P., Barry, N., Rahimi, M., Pindor, B., Trott, C.M., et al., 2016, “First Season MWA EoR Power Spectrum Results at Redshift 7″, ApJ, 833, 102
19. Jacobs, D.C., Hazelton, B.J., Trott, C.M., et al., 2016, “The Murchison Widefield Array 21 cm Power Spectrum Analysis Methodology”, The Astrophysical Journal, 825, 114
20. Offringa, A.R., Trott, C.M., et al., 2016, “Parametrizing Epoch of Reionization foregrounds: a deep survey of low-frequency point-source spectra with the Murchison Widefield Array”, MNRAS, 458, 1057
21. Trott, C.M., et al (40 authors)., 2016, “CHIPS: The Cosmological HI Power Spectrum Estimator”, The Astrophysical Journal, 818, 139
22. C.M. Trott, R.B. Wayth, and S.J. Tingay. “The Impact of Point-source Subtraction Residuals on 21 cm Epoch of Reionization Estimation”, 2012, The Astrophysical Journal, 757:101, 16 pages; Impact factor: 6.41, Citations: 80
