Deeply Buried Nuclei in the Infrared-Luminous Galaxies NGC 4418 and Arp
  220: II. Line Forests at $\lambda = $1.4--0.4 mm and Circumnuclear Gas
  Observed with ALMA
  We present the line observations in our ALMA imaging spectral scan toward
three deeply buried nuclei in NGC 4418 and Arp 220. We cover 67 GHz in $f_{\rm
rest}$=215-697 GHz at about 0.2$"$ (30, 80 pc) resolution. All the nuclei show
dense line forests; we report our initial line identification using 55 species.
The line velocities generally indicate gas rotation around each nucleus,
tracing nuclear disks of $\sim$100 pc sizes. We confirmed the counter-rotation
of the nuclear disks in Arp 220 and that of the nuclear disk and the galactic
disk in NGC 4418. While the brightest lines exceed 100 K, most of the major
lines and many $^{13}$C isotopologues show absorption against even brighter
continuum cores of the nuclei. The lines with higher upper-level energies,
including those from vibrationally-excited molecules, tend to arise from
smaller areas, indicating radially varying conditions in these nuclei. The
outflows from the two Arp 220 nuclei cause blueshifted line absorption below
the continuum level. The absorption mostly has small spatial offsets from the
continuum peaks to indicate the outflow orientations. The bipolar outflow from
the western nucleus is also imaged in multiple emission lines, showing the
extent of $\sim$1$"$ (400 pc). Redshifted line absorption against the nucleus
of NGC 4418 indicates either an inward gas motion or a small collimated outflow
slanted to the nuclear disk. We also resolved some previous confusions due to
line blending and misidentification.
