ALMA C II 158 μm Imaging of an H I-selected Major Merger at z ∼ 4
Abstract
We present high spatial resolution (≈2 kpc) Atacama Large Millimeter/submillimeter Array (ALMA) observations of [C II] 158 μm and dust-continuum emission from a galaxy at z=3.7978 selected by its strong H I absorption (a damped Lyα absorber, DLA) against a background QSO. Our ALMA images reveal a pair of star-forming galaxies separated by ≈ 6 kpc (projected) undergoing a major merger. Between these galaxies is a third emission component with highly elevated (2×) [C II] 158 μm emission relative to the dust continuum, which is likely to arise from stripped gas associated with the merger. This merger of two otherwise-normal galaxies is not accompanied by enhanced star formation, contrary to mergers detected in most luminosity-selected samples. The DLA associated with the merger exhibits extreme kinematics, with a velocity width for the low-ionization metal lines of {{Δ }}{v}90≈ 470 {km} {{{s}}}-1, that spans the velocity spread revealed in the [C II] 158 μm emission. We propose that DLAs with high {{Δ }}{v}90 values are a signpost of major mergers in normal galaxies at high redshifts, and use the distribution of the velocity widths of metal lines in high-z DLAs to provide a rough estimate the fraction of z > 3 galaxies that are undergoing a major merger.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2019
- DOI:
- 10.3847/2041-8213/ab55eb
- arXiv:
- arXiv:2005.10279
- Bibcode:
- 2019ApJ...886L..35P
- Keywords:
-
- Galaxy mergers;
- Quasar absorption line spectroscopy;
- Damped Lyman-alpha systems;
- 608;
- 1317;
- 349;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Published in ApJL: https://ui.adsabs.harvard.edu/abs/2019ApJ...886L..35P/abstract