CONCERTO

CONCERTO, which saw first light in April 2021, is one of the instruments on the Atacama Pathfinder Experiment (APEX) operated by ESO and located in the 5100-metre high Chanjantor plateau in the Chilean Andes. Its primary goal is to study the epoch of cosmic reonisation, the yet mysterious era in the history of the Universe when the first stars lit up, between 600 million and 1.2 billion years after the Big Bang.

“The aim is to study the birth of the first generations of stars,” says Guilaine Lagache from the Laboratoire d’Astrophysique de Marseille, in France, CONCERTO’s Principal Investigator. “But CONCERTO will also be used for other scientific goals, such as mapping distant galaxy clusters, to probe the physics of the intra-cluster gas and the large-scale bulk flows, and star-forming regions in our Milky Way, to study the dust properties and its link with star formation.”

CONCERTO is a spectrometer operating at frequencies between infrared and radio waves (specifically, between 130 and 310 GHz). This is the window into which the radiation emitted by ionised carbon atoms, one of the most valuable tracers of star formation in the early cosmic ages, is redshifted due to the expansion of the Universe.

Unlike the other instruments at APEX, it concentrates on both imaging and spectroscopy. “With a 20 arcminute field of view, CONCERTO is by a margin the largest field of view ever used at APEX,” says ESO Astronomer and APEX Project Scientist Carlos De Breuck. CONCERTO’s Instrument Scientist Alessandro Monfardini, from Institut Néel in Grenoble, France, highlights that “CONCERTO is the only instrument in the world capable of covering a large field-of-view and at the same time providing low-resolution spectroscopy at millimiter and sub-millimiter wavelengths.”

To conduct its operations, CONCERTO uses a totally innovative and experimental observing strategy, called intensity mapping. “In the flourishing of new ideas in the intensity-mapping field, CONCERTO lies at the forefront”, says Lagache. “With intensity mapping we will measure the signal from a large number of unresolved sources. This means that we will not observe individual galaxies but will measure their cumulative emission at each line of sight and at a given age of the Universe. CONCERTO is the first and only instrument in the world to perform intensity mapping of ionised carbon on a large field of the sky.”

CONCERTO features two arrays of detectors, cooled down with a cryostat which does not require liquid helium or nitrogen and assures continuous operation, with no dead time. “The detectors are kept at a temperature of 60 thousandths of a degree above absolute zero, equal to -273.15℃. This is surely the coldest temperature at any elevation above 5000 meters on Earth!” concludes De Breuck.