2020ApJ...898...33C

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 ∼1′′ / . 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 Sersic index ≃0.95 and Sersic 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 ∼10¹²M_☉. 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 ±0.6)×10³M_☉ yr^–1 and provide an independent estimate of the size of the star-forming region 0.7_–0.3^+0.3 kpc in radius.