Experiment to Detect the Global EoR Signature

The Experiment to Detect the Global EoR Signature (EDGES) is an experiment and radio telescope located in a radio quiet zone at the Murchison Radio-astronomy Observatory in Western Australia. It is a collaboration between Arizona State University and Haystack Observatory, with infrastructure provided by CSIRO.[1] EoR stands for epoch of reionization, a time in cosmic history when neutral atomic hydrogen gas became ionised due to ultraviolet light from the first stars.

Experiment to Detect the Global EoR Signature
Alternative namesEDGES
Part ofMurchison Radio-astronomy Observatory 
Location(s)Australia
Coordinates26°41′50″S 116°38′21″E
Telescope styleradio telescope 
Websitewww.haystack.mit.edu/astronomy/astronomy-projects/edges-experiment-to-detect-the-global-eor-signature/
Location of Experiment to Detect the Global EoR Signature
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Low-band instruments

The experiment has two low-band instruments, each of which has a dipole antenna pointed to the zenith and observing a single polarisation.[2] The antenna is around 2 by 1 metre (6.6 ft × 3.3 ft) in size, sat on a 30 by 30 metres (98 ft × 98 ft) ground shield. It is coupled with a radio receiver, with a 100m cable run to a digital spectrometer.[1] The instruments operate at 50–100 MHz (6.0–3.0 m), and are separated by 150m. Observations started in August 2015.[2]

78 MHz absorption profile

In March 2018 the collaboration published a paper in Nature announcing the discovery of a broad absorption profile centered at a frequency of MHz in the sky-averaged signal after subtracting Galactic synchrotron emission. The absorption profile has a width of MHz and an amplitude of K, against a background RMS of 0.025K, giving it a signal-to-noise ratio of 37. The equivalent redshift is centered at , spanning z=20–15. The signal is possibly due to ultraviolet light from the first stars in the Universe altering the emission of the 21cm line by lowering the temperature of the hydrogen relative to the cosmic microwave background (the mechanism is Wouthuysen–Field coupling). A "more exotic scenario," encouraged by the unexpected strength of the absorption, is that the signal is due to interactions between dark matter and baryons.[2][3]

High-band instruments

The high-band instrument is of similar design, and operates at 90–200 MHz (3.3–1.5 m).[2]

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References
  1. "MIT Haystack Observatory: EDGES". www.haystack.mit.edu. Retrieved 2 March 2018.
  2. Bowman, Judd D.; Rogers, Alan E. E.; Monsalve, Raul A.; Mozdzen, Thomas J.; Mahesh, Nivedita (1 March 2018). "An absorption profile centred at 78 megahertz in the sky-averaged spectrum". Nature. 555 (7694): 67–70. arXiv:1810.05912. Bibcode:2018Natur.555...67B. doi:10.1038/nature25792. ISSN 1476-4687. PMID 29493587.
  3. Barkana, Rennan (1 March 2018). "Possible interaction between baryons and dark-matter particles revealed by the first stars". Nature. 555 (7694): 71–74. arXiv:1803.06698. Bibcode:2018Natur.555...71B. doi:10.1038/nature25791. ISSN 1476-4687. PMID 29493590.
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