APM08279+5255 and NCv1.143 spectra

The spectra reveal the chemical richness and the complexity of the physical properties of the ISM. By comparing the spectra of the two sources and combining the analysis of the molecular gas excitation, we find that the physical properties and the chemical imprints of the ISM are different between them: the molecular gas is more excited in APM 08279+5255, exhibiting higher molecular gas temperatures and densities compared to NCv1.143; the molecular abundances in APM 08279+5255 are akin to the values of local active galactic nuclei (AGN), showing boosted relative abundances of the dense gas tracers that might be related to high-temperature chemistry and/or the X-ray-dominated regions, while NCv1.143 more closely resembles local starburst galaxies.

The most significant differences between the two sources are found in H_2_O, where the 448GHz ortho-H_2_O(423-330) line is significantly brighter in APM 08279+5255, likely linked to the intense far-infrared radiation from the dust powered by AGN. Our astrochemical model suggests that, at such high column densities, FUV radiation is less important in regulating the ISM, while cosmic rays (and/or X-rays and shocks) are the key players in shaping the molecular abundances and the initial conditions of star formation.

Both our observed CO isotopologues line ratios and the derived extreme ISM conditions (high gas temperature and density, high cosmic-ray ionization rate) suggest the presence of a top-heavy initial mass function. From the ~330-550GHz continuum, we also find evidence of non-thermal millimeter flux excess in APM 08279+5255 that might be related to the central supermassive black hole. Such deep spectral line surveys open a new window to study the physics and chemistry of the ISM and the radiation field of galaxies in the early Universe.