Leiden Observatory has achieved a rare feat: two of its research teams have been awarded prestigious ALMA Large Programmes, allowing them to study how galaxies formed and evolved in the early Universe using cutting-edge telescope observations.
'It is truly exceptional that both programmes come from Leiden,' says Michiel Hogerheijde, Programme Director of Allegro, the European ALMA support centre in the Netherlands. 'We look forward to helping both teams plan and process their observations.'
Peering into the universe's childhood
ALMA (Atacama Large Millimeter/submillimeter Array) is one of the world's most powerful telescopes. Located 5,000 metres high in the Chilean Andes, it uses dozens of antennas to detect light invisible to the human eye. This light reveals how much gas and dust is present in galaxies - the fuel needed to form new stars.
The two Leiden teams each received a Large Programme, which allows them to observe for longer periods than usual. The first is HIDING in the HUDF (Hubble Ultra Deep Field), led by Leindert Boogaard. The second is PHOENIX, led by Sander Schouws. Both programmes complement observations from the James Webb Space Telescope (JWST), which since 2021 has been exploring the early Universe in unprecedented detail. The programmes are conducted by international teams lead by Boogaard and Schouws.
HIDING in the HUDF: Resolving distant star formation
Boogaard's team is studying galaxies that existed around ten billion years ago, during the Universe's peak of star formation. But many of these stars are hidden behind thick clouds of dust. 'They are often concealed by large amounts of dust,' explains Boogaard. 'With the Hubble Space Telescope, we could mainly see the escaping light, which gives an incomplete picture.'
'With the Hubble Space Telescope, we could mainly see the escaping light, which gives an incomplete picture.'
JWST has already allowed astronomers to map star formation in these galaxies more clearly. Now, HIDING in the HUDF adds something crucial: high-resolution ALMA images of the dust itself. 'We want to find out how efficiently galaxies turn their gas and dust into stars,' Boogaard says. 'Our star formation laws are based mostly on nearby galaxies. But distant galaxies are forming stars much more actively, so the rules might be different in the early Universe.'
PHOENIX: How the first galaxies formed so quickly
Schouws focuses on an even earlier period, just a few hundred million years after the Big Bang. 'At that time, the Universe was only about two per cent of its current age,' he explains. 'Yet JWST shows surprisingly massive galaxies already existed. How did they form so quickly?'
Cosmic dust plays a key role. It helps stars form but also hides them from view. How dust formed in the early Universe is still debated: is it through supernova explosions or by growing in space between stars?
'With PHOENIX we hope to finally solve this mystery,' says Schouws. 'We will also study the conditions for star formation: how much metals were present, how dense the gas was, and how strong the ultraviolet light from young stars shone.'
Leiden at the forefront of early universe research
For Leiden Observatory, having two programmes approved is a major recognition 'Thanks to these new programmes, Leiden remains a world leader in the study of galaxy formation,' says Schouws. 'We can now take a real leap forward.'
Boogaard adds: 'It is extraordinary to witness this. Five years ago, JWST hadn't even launched. Now, by combining JWST and ALMA, we can for the first time study the physics of distant galaxies in great detail.'
The institute previously led the REBELS Large Programme (2019), which paved the way for the PHOENIX programme, whereas the HIDING in the HUDF is based on the previous ASPECS programme, in which Leiden had a leading role.
