The KAGG Survey: KCWI Analysis of Gas around Galaxies at z ≈ 3–5

We present the KCWI Analysis of Gas around Galaxies (KAGG) survey of Ly α emission around damped Ly α absorbers (DLAs) at z ≈ 3–5 with the Keck Cosmic Web Imager (KCWI) integral-field spectrograph. The KAGG survey is characterized by the sample of 36 DLAs spanning a wide metallicity range, the wide search area for associated Ly α emission (impact parameter b ≲ 120 kpc), and the high emission sensitivity, reaching Ly α luminosities ≤10 42 erg s −1 . We identify seven DLA Ly α emitters that are likely DLA galaxy candidates due to the good match between the Ly α emission and DLA redshifts. Based on a composite sample of 11 DLA Ly α emitters from KAGG and MUSE Analysis of Gas around Galaxies (MAGG), we find that the impact parameters of DLA Ly α emitters decrease with DLA metallicity, from b > 50 kpc at [M/H] ≈ −2 to b < 50 kpc at [M/H] ≈ −1. Including Ly α emitters at larger velocity offsets and at larger impact parameters from the DLAs, we construct samples of 35 “group” Ly α emitters and 17 “large-scale” Ly α emitters. We find that their impact parameters and incidence rates also depend on DLA metallicity. Based on simulations of our survey and comparisons with models of galaxy formation, we conclude that higher DLA metallicities are associated with higher halo masses. The low Ly α emission detection rate at low impact parameters suggests that most DLA galaxies either have low stellar masses ( M ≲ 10 8 M ⊙ ) or have their Ly α emission suppressed due to H i resonant scattering and/or dust absorption.