2022ApJ...927..152M

We report new Northern Extended Millimeter Array observations of the [C II]_158 µm_, [N II]_205 µm_, and [O I]_146 µm_ atomic fine structure lines (FSLs) and dust continuum emission of J1148+5251, a z = 6.42 quasar, which probe the physical properties of its interstellar medium (ISM). The radially averaged [C II]_158 µm_ and dust continuum emission have similar extensions (up to θ={2.51}_{-0.25}^{+0.46} arcsec, corresponding to r={9.8}_{-2.1}^{+3.3} kpc, accounting for beam convolution), confirming that J1148+5251 is the quasar with the largest [C II]_158 µm_-emitting reservoir known at these epochs. Moreover, if the [C II]_158 µm_ emission is examined only along its NE-SW axis, a significant excess (>5.8σ) of [C II]_158 µm_ emission (with respect to the dust) is detected. The new wide-bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad [C II]_158 µm_ line wings that were reported in previous studies. We also report the first detection of the [O I]_146 µm_ and (tentatively) [N II]_205 µm_ emission lines in J1148+5251. Using FSL ratios of the [C II]_158 µm_, [N II]_205 µm_, [O I]_146 µm_, and previously measured [C I]_369 µm_ emission lines, we show that J1148+5251 has similar ISM conditions compared to lower-redshift (ultra)luminous infrared galaxies. CLOUDY modeling of the FSL ratios excludes X-ray-dominated regions and favors photodissociation regions as the origin of the FSL emission. We find that a high radiation field (10^3.5–4.5G₀), a high gas density (n ≃ 10^3.5–4.5 cm^–3), and an H I column density of 10²³ cm^–2 reproduce the observed FSL ratios well.