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We present $\sim {0.^{\prime \prime }3}$ (114 pc) resolution maps of [C i] 3P1–3P0 (hereafter [C i] (1–0)) and 12CO (1–0) obtained toward Arp 220 with the Atacama Large Millimeter/submillimeter Array. The overall distribution of the [C i] (1–0) emission is consistent with the CO (1–0). While the [C i] (1–0) and CO (1–0) luminosities of the system follow the empirical linear relation for the unresolved ULIRG sample, we find a sublinear relation between [C i] (1–0) and CO (1–0) using the spatially-resolved data. We measure the [C i] (1–0)$/$CO (1–0) luminosity ratio per pixel in star-forming environments of Arp 220 and investigate its dependence on the CO (3–2)$/$CO (1–0) ratio (RCO). On average, the [C i] (1–0)$/$CO (1–0) luminosity ratio is almost constant up to RCO ≃ 1 and then increases with RCO. According to the radiative transfer analysis, a high C i$/$CO abundance ratio is required in regions with high [C i] (1–0)$/$CO (1–0) luminosity ratios and RCO > 1, suggesting that the C i$/$CO abundance ratio varies at ∼100 pc scale in Arp 220. The [C i] (1–0)$/$CO (1–0) luminosity ratio depends on multiple factors and may not be straightforward to interpret. We also find the high-velocity components traced by [C i] (1–0) in the western nucleus, likely associated with the molecular outflow. The [C i] (1–0)$/$CO (1–0) luminosity ratio in the putative outflow is 0.87 ± 0.28, which is four times higher than the average ratio of Arp 220. While there is a possibility that the [C i] (1–0) and CO (1–0) emission traces different components, we suggest that the high line ratios are likely to be because of elevated C i$/$CO abundance ratios based on our radiative transfer analysis. A C i-rich and CO-poor gas phase in outflows could be caused by the irradiation of the cosmic rays, the shock heating, and the intense radiation field.

We present observations of [N ii] 205 μm, [O iii] 88 μm, and dust emission in a strongly-lensed, submillimeter galaxy (SMG) at z = 6.0, G09.83808, with the Atacama Large Millimeter/submillimeter Array (ALMA). Both [N ii] and [O iii] line emissions are detected at >12σ in the ${0{^{\prime \prime}_{.}}8}$-resolution maps. Lens modeling indicates that the spatial distribution of the dust continuum emission is well characterized by a compact disk with an effective radius of 0.64 ± 0.02 kpc and a high infrared surface brightness of ΣIR = (1.8 ± 0.3) × 1012 L⊙ kpc−2. This result supports that G09.83808 is the progenitor of compact quiescent galaxies at z ∼ 4, where the majority of its stars are expected to be formed through a strong and short burst of star formation. G09.83808 and other lensed SMGs show a decreasing trend in the [N ii] line to infrared luminosity ratio with increasing continuum flux density ratio between 63 and 158 μm, as seen in local luminous infrared galaxies (LIRGs). The decreasing trend can be reproduced by photoionization models with increasing ionization parameters. Furthermore, by combining the [N ii]/[O iii] luminosity ratio with far-infrared continuum flux density ratio in G09.83808, we infer that the gas phase metallicity is already Z ≈ 0.5–0.7 Z⊙. G09.83808 is likely one of the earliest galaxies that has been chemically enriched at the end of reionization.

We present CO J = 4–3 line and 3 mm dust continuum observations of a 100 kpc-scale filamentary Lyα nebula (SSA22 LAB18) at z = 3.1 using the Atacama Large Millimeter/submillimeter Array (ALMA). We detected the CO J = 4–3 line at a systemic zCO = 3.093 ± 0.001 at 11 σ from one of the ALMA continuum sources associated with the Lyα filament. We estimated the CO J = 4–3 luminosity of $L^{\prime }_{\rm {CO(4-3)}}=(2.3 \pm 0.2)\times 10^{9}\:$K km s−1 pc2 for this CO source, which is one order of magnitude smaller than those of typical z > 1 dusty star-forming galaxies (DSFGs) of similar far-infrared luminosity LIR ∼ 1012 L⊙. We derived a molecular gas mass of $M_{\rm {gas}} = (4.4^{+0.9}_{-0.6}) \times 10^{9}\, M_{{\odot }}$ and a star-formation rate of SFR =270 ± 160 M⊙ yr−1. We also estimated a gas depletion time of τdep = 17 ± 10 Myr, which is shorter than those of typical DSFGs. It is suggested that this source is in the transition phase from DSFG to a gas-poor, early-type galaxy. From ALMA to Herschel multi-band dust continuum observations, we measured a dust emissivity index β = 2.3 ± 0.2, which is similar to those of local gas-poor, early-type galaxies. From recent laboratory experiments, the specific chemical compositions needed to reproduce such a high β for interstellar dust at the submillimeter wavelengths. ALMA CO and multi-band dust continuum observations can constrain the evolutionary stage of high-redshift galaxies through τdep and β, and thus we can investigate the chemical composition of dust even in the early Universe.

We present ALMA [C ii] line and far-infrared (FIR) continuum observations of three $z \gt 6$ low-luminosity quasars ($M_{\rm 1450} \gt -25$ mag) discovered by our Subaru Hyper Suprime-Cam (HSC) survey. The [C ii] line was detected in all three targets with luminosities of $(2.4\mbox{--}9.5) \times 10^8\, L_{\odot }$, about one order of magnitude smaller than optically luminous ($M_{\rm 1450} \lesssim -25$ mag) quasars. The FIR continuum luminosities range from $\lt 9 \times 10^{10}\, L_{\odot }$ (3 $\sigma$ limit) to ${\sim } 2 \times 10^{12}\, L_{\odot }$, indicating a wide range in star formation rates in these galaxies. Most of the HSC quasars studied thus far show [C ii]/ FIR luminosity ratios similar to local star-forming galaxies. Using the [C ii]-based dynamical mass ($M_{\rm dyn}$) as a surrogate for bulge stellar mass ($M_{\rm\, bulge}$), we find that a significant fraction of low-luminosity quasars are located on or even below the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation, particularly at the massive end of the galaxy mass distribution. In contrast, previous studies of optically luminous quasars have found that black holes are overmassive relative to the local relation. Given the low luminosities of our targets, we are exploring the nature of the early co-evolution of supermassive black holes and their hosts in a less biased way. Almost all of the quasars presented in this work are growing their black hole mass at a much higher pace at $z \sim 6$ than the parallel growth model, in which supermassive black holes and their hosts grow simultaneously to match the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation at all redshifts. As the low-luminosity quasars appear to realize the local co-evolutionary relation even at $z \sim 6$, they should have experienced vigorous starbursts prior to the currently observed quasar phase to catch up with the relation.