Ionized and atomic interstellar medium in the z = 6.003 quasar SDSS J2310+1855

Observing the interstellar medium (ISM) in z & 6 quasar host galaxies is essential for understanding the coevolution between the supermassive black holes and their hosts. To probe the gas physical conditions and search for imprints of active galactic nuclei (AGN) on the ISM, we report ALMA observations of the [N II]_122µm and [O I]_146µm lines and the underlying continuum from the z = 6.003 quasar SDSS J231038.88+185519.7. Together with previous [C II]_158µm and [O III]_88µm observations, we use the ratios of these fine-structure lines to probe the ISM properties. Similar to other high-z systems, this object exhibits a [C II]_158µm/[O I]_146µm ratio comparable to the lowest values found in local (Ultra)luminous infrared galaxies, suggesting a “warmer” and “denser” gas component compared to typical local systems. The [O III]_88µm/[O I]_146µm ratio is lower than that of other local and high-z systems, indicating a smaller ionized gas fraction in this quasar. The [O III]_88µm/[N II]_122µm ratio is comparable to that of local systems, and suggests a metallicity of Z/Z_☉=1.5−2.1. Based on the [N II]_122µm detection, we estimate that 17% of the [C II]_158µm emission is associated with ionized gas. The [N II]_122µm line shows a “flux deficit” comparable to local systems. The [O I]_146µm line, with a [O I]_146µm/FIR ratio >2× than expected from the local relation, indicates no [O I]_146µm deficit. The low [C II]_158µm/[O I]_146µm ratio, together with the high [O I]_146µm/FIR ratio in J2310+1855, reveals that the warm and dense gas is likely a result of AGN heating of the ISM.