Arecibo Observatory: Atomic Hydrogen Detected At Record Distances

Credit: NAIC

Due to its vastness the universe can be thought of as a cosmic photo album: the deeper you peer into the album, the further the snapshots delve into history. This profound attribute is invaluable to astronomers: by selecting astrophysical objects at increasing distances (i.e. different epochs), a complete record of how the universe evolved can be pieced together.

What a team from Swinburne University of Technology have achieved, is the furthest detection of atomic hydrogen (HI) to date. Using the famous Arecibo radio telescope, Puerto Rico, research comprised of investigating thirty-nine ‘HIGHz’ (high redshift) galaxies, specially selected from the Sloan Digital Sky Survey for their expected gas/light correlations. As the team highlight: ‘their [HIGHz] gas content is exactly what is expected from their UV and optical properties’.

Atomic hydrogen (HI) rich galaxies selected for HIGHz Arecibo survey (Credit: Sloan Digital Sky Survey)

Looking back in time: Atomic hydrogen (HI) rich galaxies selected for the HIGHz Arecibo survey (Credit: Sloan Digital Sky Survey)

The targeted HIGHz (0.17 ≤ z ≤ 0.25) galaxies are located approximately 3 billion light years from Earth, breaking current detection distances by 500 million light years; with each system containing between 20 to 80 billion times more HI than current solar estimates.

The team report, although HI signatures were received, isolating them from background noise was challenging: ‘The signals are not only weak, but they appear at radio frequencies that are used by communication devices and radars, which generate signals billions of times stronger than the cosmic ones that we are trying to detect’, said Co-author Dr Luca Cortese.

Arecibo HI research initially began to test how far astronomers could detect relevant signals—this has been greatly surpassed: The outcome vastly exceeded our initial expectation’, said Dr Barbara Catinella, joint project researcher.

‘Atomic hydrogen gas is the fuel out of which new stars are formed, hence it is a crucial component to study if we are to understand how galaxies form and evolve’.

Deeper searches are expected in the future, when the international ‘Square Kilometre Array’ (Australia) becomes operational. This will ensure observations of high redshift objects (z > 0.2) become routine, providing astronomers with a more detailed exploration into the ‘cosmic photo album’—first light is planned for 2020.

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Paul Hattle

As a strong advocate for science and learning, I am a passionate supporter of the 'Campaign for Science and Engineering' (CaSE) Fellow of the 'Royal Astronomical Society' (RAS) Associate Member of the 'Institute of Physics' (IOP) & 'The Institute of Scientific and Technical Communicators' (ISTC)

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