​Alma’s new view of the colliding galaxy system Arp 220 (in red) combined with an image from the Hubble Space Telescope (blue/green)​
ALMA (ESO/NAOJ/NRAO)/NASA/ESA and The Hubble Heritage Team (STScI/AURA)

Searching for water in the universe: First light for Alma’s new receivers

The Alma telescope in Chile has begun observing in a new range of the electromagnetic spectrum – thanks to technology from Chalmers. With its new receivers, Alma can for the first time detect radio waves with wavelengths from 1.4 to 1.8 millimetres, allowing astronomers to detect faint signals of water in the nearby Universe.

Alma observes radio waves from the Universe, at the low-energy end of the electromagnetic spectrum. With the newly installed Band 5 receivers, Alma has now opened its eyes to a whole new section of this radio spectrum, creating exciting new observational possibilities.

“The new receivers will make it much easier to detect water, a prerequisite for life as we know it, in our Solar System and in more distant regions of our galaxy and beyond. They will also allow Alma to search for ionised carbon in the primordial Universe”, explains Leonardo Testi, European Alma Programme Scientist.

It is Alma’s unique location, 5000 metres up on the barren Chajnantor plateau in Chile, that makes such an observation possible in the first place. As water is also present in Earth’s atmosphere, observatories in less elevated and less arid environments have much more difficulty identifying the origin of the emission coming from space. Alma’s great sensitivity and high angular resolution mean that even faint signals of water in the local Universe can now be imaged at this wavelength. A key spectral signature of water lies in this expanded range – at a wavelength of 1.64 millimetres.

The Band 5 receiver, which was developed by the Group for Advanced Receiver Development (GARD) at Onsala Space Observatory, Chalmers, has already been tested at the Apex telescope in the Sepia instrument. These observations were also vital to help select suitable targets for the first receiver tests with Alma.

The first production receivers were built and delivered to ALMA in the first half of 2015 by a consortium consisting of the Netherlands Research School for Astronomy (NOVA) and GARD in partnership with the National Radio Astronomy Observatory (NRAO), which contributed the local oscillator to the project. The receivers are now installed and being prepared for use by the community of astronomers.

To test the newly installed receivers observations were made of several objects including the colliding galaxies Arp 220 (image). Other targets were a massive region of star formation close to the centre of the Milky Way, and a dusty red supergiant star approaching the supernova explosion that will end its life.

To process the data and check its quality, astronomers, along with technical specialists from ESO and the European ALMA Regional Centre (ARC) network, gathered at the Onsala Space Observatory in Sweden, for a "Band 5 Busy Week" hosted by the Nordic ARC node. The final results have just been made freely available to the astronomical community worldwide.

Team member Robert Laing at ESO is optimistic about the prospects for ALMA Band 5 observations: “It's very exciting to see these first results from ALMA Band 5 using a limited set of antennas. In the future, the high sensitivity and angular resolution of the full ALMA array will allow us to make detailed studies of water in a wide range of objects including forming and evolved stars, the interstellar medium and regions close to supermassive black holes.”

While the receivers have been installed at Alma and Apex, others originally from GARD are on their way to other telescope projects, among them Japan’s ASTE and the Argentinian-Brazilian project LLAMA. For Victor Belitsky, who has led work on Band 5 at Onsala Space Observatory and Chalmers, this is a proud moment.

“With “First Light” for Band 5, astronomers can begin to discover the universe in a new way. Our work has meant a remarkable and exciting journey, from the first design via fabrication in Chalmers’ clean room, integration of components with terahertz optics and cryogenic technology, to the installation of the complete system in the world’s most advanced radio telescopes”, he says.


1. (top) Alma’s new view of the colliding galaxy system Arp 220 (in red) on top of an image from the NASA/ESA Hubble Space Telescope (blue/green). In the Hubble image, most of the light from this dramatic merging galaxy pair is hidden behind dark clouds of dust. Alma’s observations in Band 5 show a completely different view. Here, Arp 220's famous double nucleus, invisible for Hubble, is by far the brightest feature in the whole galaxy complex. In this dense, double centre, the bright emission from water and other molecules revealed by the new Band 5 receivers will give astronomers new insights into star formation and other processes in this extreme environment. High resolution image at ESO.
Credit: ALMA (ESO/NAOJ/NRAO)/NASA/ESA and The Hubble Heritage Team (STScI/AURA)

2. A Band 5 receiver in the lab. High-resolution image at ESO.
Credit: ALMA (ESO/NAOJ/NRAO), N. Tabilo

3. GARD engineer Mathias Fredrixon tests a Band 5 receiver for Alma. High-resolution image at ESO.
Credit: Onsala Space Observatory/A. Pavolotsky

4. Alma under the Magellanic Clouds. High-resolution image at ESO.
Credit: ESO/C. Malin

More about the data processing and the receivers

The team working on processing the data included Tobia Carozzi, Simon Casey, Sabine König, Matthias Maercker, Iván Martí-Vidal, Sebastien Muller, Daniel Tafoya and Wouter Vlemmings (all Onsala Space Observatory and Chalmers scientists), together with Ana Lopez-Sepulcre, Lydia Moser and Anita Richards. The ESO Band 5 Science Verification team includes Elizabeth Humphreys, Tony Mroczkowski, Robert Laing, Katharina Immer, Hau-Yu (Baobab) Liu, Andy Biggs, Gianni Marconi and Leonardo Testi. The observations were performed and made possible by the ALMA Extension of Capabilities team in Chile.

Read more about the Band 5 receivers on Alma and Apex in our article “Desert telescopes ready to discover water in space”, http://www.chalmers.se/en/centres/oso/news/Pages/apex-sepia-alma-band-5-water-space.aspx

More about Alma and Onsala Space Observatory
The Atacama Large Millimeter/submillimeter Array (Alma), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. Alma is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

Chalmers and Onsala Space Observatory have been involved in Alma since its inception; receivers for the telescope are one of many contributions. Onsala Space Observatory is host to the Nordic Alma Regional Centre, which provides technical expertise to the Alma project and supports astronomers in the Nordic countries in using Alma.

Onsala Space Observatory is Sweden's national facility for radio astronomy. The observatory provides researchers with equipment for the study of the earth and the rest of the universe. In Onsala, 45 km south of Gothenburg, it operates two radio telescopes and a station in the international telescope Lofar. It also participates in several international projects. The observatory is hosted by Department of Earth and Space Sciences at Chalmers University of Technology, and is operated on behalf of the Swedish Research Council.


Robert Cumming, astronomer and communications officer, Onsala Space Observatory, +46 31 772 5500, +46 70 49 33 114, robert.cumming@chalmers.se

Victor Belitsky, professor of radio and space science, Chalmers, leader for Group for Advanced Receiver Development (GARD)  at Onsala Space Observatory and Chalmers, +46 31-772 1893, victor.belitsky@chalmers.se​

Published: Wed 21 Dec 2016. Modified: Wed 21 Dec 2016