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Intensity mapping of the atomic carbon CII line: the promise of a new observational probe of dusty star-formation in post-reionization and reionization epoch

Periodic Reporting for period 1 - CONCERTO (Intensity mapping of the atomic carbon CII line: the promise of a new observational probe of dusty star-formation in post-reionization and reionization epoch)

Reporting period: 2019-01-01 to 2020-06-30

CONCERTO aims to answer the outstanding questions of whether dusty star-formation contributes to early galaxy evolution, and whether dusty galaxies play an important role in shaping cosmic reionisation, which is a critical transition in the life of the Universe. To reach that goal, we are constructing a spectrometer to map in 3D the intensity due to line emission, a technique known as Intensity Mapping. Instead of detecting individual galaxies, this emerging technique measures signal fluctuations produced by the combined emission of the galaxy population on large regions of the sky in a wide redshift band, and thus increases sensitivity to faint sources. Capitalizing on a recent technology breakthrough, our intensity mapping experiment will measure the 3D fluctuations of the [CII] line in the first Gyr of the Universe. [CII] is one of the most valuable tracers of star formation. We will use the [CII] line emission as a tracer of cosmic density structure and give the first constraints on the power spectrum of dusty star-forming matter. Our experiment will also observe the CO intensity fluctuations arising from galaxies in the older Universe (with age >3 Gyr), giving the spatial distribution and abundance of molecular gas over a broad range of cosmic time.

We are building, testing and will finally install the instrument on the APEX antenna, following an agreement with APEX partners. The spectrometer is based on state-of-the-art development of new arrays in the millimeter using kinetic inductance detectors. Spectra are obtained using a fast Martin-Puplett interferometer. Then, we will observe a few square degrees with CONCERTO and offer straightforward alternative for probing star formation and dust build-up in the early Universe. Finally, CONCERTO will set to music the various cosmic evolution probes. Cross-correlation of the signals will be used in particular to capture the topology of the end of reionisation era. Our novel technology targets an unexplored observable touching on some fundamental processes building the early Universe. In the flourishing of new ideas in the intensity mapping field, CONCERTO lies at the forefront.
Most of the activities has been dedicated to the design, test and fabrication of the instrument.
Building such a complex instrument in a very short time is a great challenge. As of today, the mounting of the instrument is well advanced with the complete electronics, interferometer mechanics, cryostat, KIDS camera (4,300 pixels), and optical box already assembled (see the figure). The polarisers are fabricated. First tests on the camera give sensitivity in line with expectation. We presented our current results on the instrument, together with scientific forecast on the [CII] survey, in “A wide field-of-view low-resolution spectrometer at APEX: Instrument design and scientific forecast”, in the Astronomy & Astrophysics journal. We successfully passed the APEX reviews (from the preliminary design up to the final acceptance) and started the installation at APEX by mounting all the pipes in the cabin of the telescope in February 2020. We participated to the ESO call for proposal and were successfully granted 600 hours of observing time by ESO on APEX to conduct our [CII] survey. In parallel, we are developing the pipeline for data reduction that we are testing on data coming from our pathfinder instrument for CONCERTO, named KISS, and have obtained the first spectrum with KISS. We have built new realistic simulations of the extragalactic sky that include both dust continuum and [CII] and CO spectral features (see the figure). These simulations are unique and will serve as a reference for (sub)-millimeter intensity mapping experiments.
CONCERTO is one of the two instruments in the world to perform intensity mapping of the [CII] line in the short term. It represents a unique opportunity before new experiments will come through (e.g. on the CCAT-p telescope, that should be built up after 2021). The timeline for CONCERTO instrument development and installation is extremely challenging but we managed so far to be on schedule. Before the COVID-19 crisis, the installation was foreseen to start on Feb. 2020 the 16th. Hopefully, the situation at APEX will improve (all scientific operations are ceased since mid-March 2020) such that we can meet this date. The Observing Program Office from ESO stated that “CONCERTO will bring a new life to APEX, particularly in the ALMA world. As such, this is a very interesting instrument and its installation should be supported”. Once installed, we will proceed to the technical and scientific commissioning and finally conduct the [CII] survey. We expect our experiment to give a unique large-scale view of dusty star formation in the early Universe but it must overcome several observational challenges, especially effects linked to the atmosphere and contaminations from extragalactic foregrounds. We are preparing ourselves to tackle these challenges. Even if penetrating deep into the epoch of reionisation is uncertain, mainly due to our ignorance regarding the expected signal amplitude, the endeavor is well worth the effort. After years of predictions (more than 100 papers on 3D intensity mapping), the time has come for measurements!
Data cube Simulation: simulated map at 310 GHz w/ dust continuum,[CII],distant galaxies CO2 emission
CONCERTO instrument building (06/2020): chassis,cryostat,electronics,foldable mirror,interferometer