ALMA [N ii] 205 μm Imaging Spectroscopy of the Lensed Submillimeter Galaxy ID 141 at Redshift 4.24

We present an Atacama Large Millimeter/submillimeter Array observation of the Submillimeter galaxy ID 141 at z = 4.24 in the [N ii] 205 μm line (hereafter [N ii] ) and the underlying continuum at (rest-frame) 197.6 μm. Benefiting from lensing magnification by a galaxy pair at z = 0.595, ID 141 is one of the brightest $z>4$ SMGs. At the angular resolutions of $\sim 1\stackrel{\prime \prime }{.}2$–1.″5 (1″ ∼6.9 kpc), our observation clearly separates and moderately resolves the two lensed images in both continuum and line emission at a signal-to-noise ratio >5. Our continuum-based lensing model implies an averaged amplification factor of ∼5.8 and reveals that the delensed continuum image has a Sérsic index $\simeq 0.95$ and Sérsic radius of ∼0.″18 (∼1.24 kpc). Furthermore, the reconstructed [N ii] velocity field in the source plane is dominated by a rotation component with a maximum velocity of ∼300 km s⁻¹ at large radii, indicating a dark matter halo mass of ∼10${}^{12}{M}_{\odot }$. This, together with the reconstructed velocity dispersion field being smooth and modest in value (<100 km s⁻¹) over much of the outer parts of the galaxy, favors the interpretation of ID 141 being a disk galaxy dynamically supported by rotation. The observed [N ii] /CO (7−6) and [N ii] /[C ii] 158 μm line-luminosity ratios, which are consistent with the corresponding line ratio versus far-infrared color correlation from local luminous infrared galaxies, imply a delensed star formation rate of (1.8 $\pm 0.6)\times {10}^3{M}_{\odot }$ yr⁻¹ and provide an independent estimate of the size of the star-forming region ${0.7}_{-0.3}^{+0.3}$ kpc in radius.