Rychard Bouwens from the Leiden Observatory is the first scientist in the Netherlands to be assigned a Large Programme on the state-of-the-art ALMA telescope in Chile. With his team, he wants to use the unique capabilities of the billion-euro facility to investigate the build-up of massive galaxies in the early universe. Time at ALMA is precious: ‘Typically only two to four large programmes are approved for execution each year from scientists all around the world’, Bouwens says.
Census for galaxies
An important question in astronomy is how quickly galaxies grow from almost nothing at the beginning of the universe, to masses equalling some 10 billion times the mass of our sun just 800 million years later. ‘With our programme, we aim to identify the dustiest and most massive galaxies in the first 800 million years of the universe,’ Bouwens tells. ‘The census we will perform with ALMA, will allow us to determine how fast the dust and total mass in stars has built up.’ By acquiring these new data, Bouwens hopes to resolve many of the ongoing debates in galaxy formation studies.
Bouwens will execute his scientific programme over the next 2 years. The allocation is in the Large Programme category, which is highly competitive (see box): ‘ALMA is a billion-euro facility doing absolutely state-of-the-art science, and only two to four ambitious programmes can be executed each year. This includes scientists from all around the world in all subjects of astronomy.’ Only 13 Large Programmes have been approved in the entire history of the ALMA facility. Bouwens: ‘ALMA is the only existing observational facility capable of characterizing the properties of massive galaxies in the first billion years of the universe. It thereby provides essential insights into the dust content and dynamical properties of these galaxies. Other telescopes are either not sensitive enough, or do not probe the right wavelength range.’ Because of the large allocation of telescope time, Bouwens’ team can study six times more sources than before and perform the study in a systematic way.
High on the Chajnantor plateau in the Chilean Andes, the European Southern Observatory (ESO), together with its international partners, is operating the Atacama Large Millimeter/submillimeter Array (ALMA) – a state-of-the-art telescope to study light from some of the coldest objects in the Universe. This light has wavelengths of around a millimetre, between infrared light and radio waves, and is therefore known as millimetre and submillimetre radiation. ALMA comprises 66 high-precision antennas, spread over distances of up to 16 kilometres. This global collaboration is the largest ground-based astronomical project in existence.
Because so many aspects of growing galaxies in the early universe are not well understood, Bouwens will focus on multiple questions. The first is the total mass of the brightest galaxies. ‘Since with other telescopes, we primarily observe the ultraviolet light of these galaxies, we have a difficult time determining their masses. Knowing these masses can help compare what we observe with the theoretical models.’ Another mystery to be solved is how the material in massive galaxies moves. Does it rotate smoothly, like the matter in disk galaxies? Or are the movements of the matter less coherent? ‘At much later points in cosmic time, there is a mix of galaxies with smoother and more random movements’, Bouwens explains. ‘Theoretical models suggest random motions, but many of the galaxies we have observed so far surprisingly have shown more smooth rotation.’
The final big question considers how quickly dust grains emerge in rapidly growing, high-mass galaxies. Dust grains form from heavy elements ejected by hot stars. ‘There are many open questions about how long it takes dust grains to build up. Our observational programme should completely revolutionise our constraints on the build-up of dust.’
Scientific director of the Leiden Observatory, Huub Röttgering, is excited about the news. ‘It’s wonderful to see that ALMA is now finally going to systematically investigate the role of dust and cold gas in the formation of the very first galaxies. It is great that the Netherlands, represented by Rychard Bouwens, play such a prominent role in this competitive research field.’ In order to accomplish this, Bouwens hopes to successfully apply for funding from the ERC in the form of an Advanced Grant. ‘The ALMA observational programme will require considerable manpower to realise the full potential of the programme.’
ALMA’s Large Programmes
Large Programmes are designed to address strategic scientific issues that will lead to a major advance or breakthrough in the field. The Large Programme proposal teams produce high level data products and documentation which are made available to the scientific community within one year after the final delivery of calibrated data.
For the programme, Bouwens collaborates with three other principal investigators: Hanae Inami (Hiroshima, Japan), Dan Stark (U Arizona, USA), and Valentino Gonzalez (U Chile, Chile). The group builds upon the work of Renske Smit. After finishing her PhD at Leiden Observatory, Smit made important pathfinding discoveries with ALMA, which paved the way for the new Large Programme. Last year, Smit published a paper on rotating galaxies in Nature: Rotation in [C II]-emitting gas in two galaxies at a redshift of 6.8.