The discovery of galaxies formed when the Universe was less than 1 Gyr old has been a major breakthrough of extragalactic astronomy. During this period, called Epoch of Reionization (EoR), the Universe experienced a dramatic change: from being a dark “sea” of neutral hydrogen and helium, it got completely reionized and polluted with elements heavier than helium. Thus, characterising the bulk of galaxy population at these early epochs is pivotal because of their strong impact on the cosmic evolution. The most distant galaxies have been detected searching for their Lyman-α emission (Lyman Alpha Emitters; LAEs), and/or for the “step”, introduced by the blanketing effect of neutral hydrogen into their UV continuum emission (Lyman Break Galaxies; LBGs). LAEs/LBGs are quite “normal” objects, therefore they are thought to be fairly representative of the bulk of galaxies at the end of the EoR. Our knowledge about these sources regards their stellar component (star formation rates, stellar age and mass). However, we have few clues about their interstellar medium, the properties of the giant molecular clouds (GMCs) where stars form, and, most importantly, the possible presence of faint Active Galactic Nuclei (AGN).
With this project called DeepIMPACT (Deep Investigation on Molecular Processes At early Cosmic Times) we study the properties of faint AGNs through their signature in the molecular emission spectrum.
This is of utmost importance because only extremely luminous AGN, in which the gas is accreting onto a Super Massive Black Hole (SMBH), have been detected at z>6.
Their formation is still puzzling, and the better strategy to look for SMBH seeds, and in general for lower luminosity AGN, is matter of ongoing debate in the astrophysical community.
The overall objectives of DeepIMPACT can be summarised as follows:
1) Model the chemical, physical, and radiative processes in giant molecular clouds illuminated by both young stars and AGN.
2) Quantify the impact of X-ray photons on the clumpy structure of molecular clouds,
3) Clarify whether the AGN signature can be observed in the molecular emission and pinpoint galaxy candidates for observational follow up targeting the molecular gas.
