Using data from the 64-m CSIRO radio telescope in Australia and the 100-m Max-Planck radio telescope in Germany, an international team of astronomers has created a detailed density map of neutral atomic hydrogen in our Milky Way Galaxy.

The study looked at neutral atomic hydrogen, the most abundant element in space, across the whole sky in a survey known as HI4PI.

“Although neutral hydrogen is fairly easy to detect with modern radio telescopes, mapping the whole sky is a significant achievement,” said co-author Dr. Juergen Kerp, an astronomer at the University of Bonn.

“Radio noise caused by mobiles and broadcast stations pollutes the faint emissions coming from stars and galaxies in the Universe.”

“So sophisticated computer algorithms have to be developed to clean each individual data point of this unwanted human interference.”

HI4PI collected data on clouds of hydrogen gas at full resolution, allowing astronomers to learn more about the physics of what is going on in those areas, where the structures are coming from and more.

“The study revealed for the first time the fine details of structures between stars in the Milky Way,” said co-author Prof. Naomi McClure-Griffiths, from the Australian National University.

“Very small gas clouds appear to have helped form stars in the Milky Way over billions of years.”

The study required more than a million individual observations and about 10 billion individual data points.

It improves the previous neutral hydrogen study, the Leiden-Argentine-Bonn (LAB) survey, by a factor of two in sensitivity and a factor of four in angular resolution.

“The study reveals fine details of structures between stars in the Milky Way for the first time. These structures had been smeared out by the coarse sampling of the sky in the LAB survey,” said senior author Prof. Lister Staveley-Smith, from the International Centre for Radio Astronomy Research.

“Pilot studies of the HI4PI data show a wealth of filamentary structures never seen before.”

“Having a clearer picture of the hydrogen in the Milky Way would also help astronomers to explore galaxies even at cosmological distances,” said corresponding co-author Dr. Benjamin Winkel, from the Max Planck Institute for Radio Astronomy.

“Like the clouds at the sky, all observations we receive from the distant Universe have to pass through hydrogen in our own Milky Way.”

“The HI4PI data allows us to correct accurately for all these hydrogen clouds and clean the window we are watching through.”

“HI4PI sets a benchmark for the decades to come,” Dr. Kerp added.

“Although upcoming new instruments such as the Square Kilometer Array (SKA) will push sensitivity and angular resolution to new realms, being radio interferometers they are by design insensitive to diffusely distributed HI gas. The HI4PI will be the prime resource to add this missing information to the SKA data.”

The research appears today in the journal Astronomy and Astrophysics.

_____

N. Ben Bekhti et al (HI4PI Collaboration). 2016. HI4PI: a full-sky H i survey based on EBHIS and GASS. A&A 594, A116; doi: 10.1051/0004-6361/201629178