Lyman-α at cosmic noon I: Lyα spectral type selection ofz∼ 2 – 3 Lyman break galaxies with broadband imaging

Abstract

High-redshift Lyman break galaxies (LBGs) are efficiently selected in deep images using as few as three broadband filters, and have been shown to have multiple intrinsic and small- to large-scale environmental properties related to Lyman-α. In this paper we demonstrate a statistical relationship between net Lyman-α equivalent width (net Lyα EW) and the optical broadband photometric properties of LBGs at z ∼ 2. We show that LBGs with the strongest net Lyα EWin absorption (aLBGs) and strongest net Lyα EWin emission (eLBGs) separate into overlapping but discrete distributions in (U n – ${\mathcal R}$ ) colour and ${\mathcal R}$ -band magnitude space, and use this segregation behaviour to determine photometric selection criteria by which sub-samples with a desired Lyα spectral type can be selected using data from as few as three broadband optical filters. We propose application of our result to current and future large-area and all-sky photometric surveys that will select hundreds of millions of LBGs across many hundreds to thousands of Mpc, and for which spectroscopic follow-up to obtain Lyα spectral information is prohibitive. To this end, we use spectrophotometry of composite spectra derived from a sample of 798 LBGs divided into quartiles on the basis of net Lyα EWto calculate selection criteria for the isolation of Lyα-absorbing and Lyα-emitting populations of z ∼ 3 LBGs using ugri broadband photometric data from the Vera Rubin Observatory Legacy Survey of Space and Time (LSST).

Lyman-α at Cosmic Noon II: The relationship between kinematics and Lyman-α in z ∼ 2–3 Lyman break galaxies

“…In Paper I in this series (Foran et al 2023), we report the photometric segregation of LBGs versus net Ly EW in rest-frame UV colour–magnitude space, and derive criteria for the selection of pure samples of LBGs with Ly dominant in absorption and Ly dominant in emission on the basis of optical broadband imaging alone. Together with the analogous result of Cooke (2009), we have suggested the utility of this method to study a wide range of properties known to be associated with Ly (see Section 3.3.3), in large samples and over large scales in datasets from current and future large-area and all-sky photometric surveys such as the Vera Rubin Observatory Legacy Survey of Space and Time (LSST: Ivezić et al 2019).…”