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

Abstract

We present an Atacama Large Millimeter/submillimeter Array observation of the Submillimeter galaxy ID 141 at z  = 4.24 in the [N ii ] 205 μ m line (hereafter [N ii ] ) and the underlying continuum at (rest-frame) 197.6 μ m. Benefiting from lensing magnification by a galaxy pair at z  = 0.595, ID 141 is one of the brightest SMGs. At the angular resolutions of –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 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 . 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 μ m 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 yr −1 and provide an independent estimate of the size of the star-forming region kpc in radius.