Lyman-α at Cosmic Noon II: The relationship between kinematics and Lyman-α in z ∼ 2-3 Lyman break galaxies
Abstract
We report for the first time a relationship between galaxy kinematics and net Lyman- α equivalent width (net Ly α EW) in star-forming galaxies during the epoch of peak cosmic star formation. Building on the previously reported broadband imaging segregation of Ly α -emitting and Ly α -absorbing Lyman break galaxies (LBGs) at z∼2 (Paper I in this series) and previously at z∼3 , we use the Ly α spectral type classification method to study the relationship between net Ly α EW and nebular emission-line kinematics in samples of z∼2 and z∼3 LBGs drawn from the literature for which matching rest-frame UV photometry, consistently measured net Ly α EWs, and kinematic classifications from integral field unit spectroscopy are available. We show that z∼2 and z∼3 LBGs segregate in colour-magnitude space according to their kinematic properties and Lyman- α spectral type and conclude that LBGs with Ly α dominant in absorption (aLBGs) are almost exclusively rotation-dominated (presumably disc-like) systems, and LBGs with Ly α dominant in emission (eLBGs) characteristically have dispersion-dominated kinematics. We quantify the relationship between the strength of rotational dynamic support (as measured using vobs}/2σint and vrot/σ0 ) and net Ly α EW for subsets of our kinematic sample where these data are available, and demonstrate the consistency of our result with other properties that scale with net Ly α EW and kinematics. Based on these findings, we suggest a method by which large samples of rotation- and dispersion-dominated galaxies might be selected using broadband imaging in as few as three filters and/or net Ly α EW alone. If confirmed with larger samples, application of this method will enable an understanding of galaxy kinematic behaviour over large scales in datasets from current and future large-area and all-sky photometric surveys that will select hundreds of millions of LBGs in redshift ranges from z∼2-6 across many hundreds to thousands of Mpc. Finally, we speculate that the combination of our result linking net Ly α EW and nebular emission-line kinematics with the known large-scale clustering behaviour of Ly α -absorbing and Ly α -emitting LBGs is evocative of an emergent bimodality of early galaxies that is consistent with a nascent morphology-density relation at z∼2-3.
- Publication:
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Publications of the Astronomical Society of Australia
- Pub Date:
- January 2024
- DOI:
- 10.1017/pasa.2023.61
- arXiv:
- arXiv:2311.15721
- Bibcode:
- 2024PASA...41....5F
- Keywords:
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- Galaxies: evolution;
- galaxies: fundamental parameters;
- galaxies: high-redshift;
- galaxies: kinematics and dynamics;
- galaxies: photometry;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Published in PASA (Version 2: Typos corrected and minor clarifying edits in S3.1 &