The BRIDGE Survey. I. Metallicities and Physical Properties of Gas Probing the Circumgalactic Medium at Cosmic Noon

We present BRIDGE-I, a metallicity survey of-selected absorbers probing ``CGM-like'' gas (16.4 at most N HI<20.3) at Cosmic Noon (1 at most z at most2.2), the epoch of peak star formation and AGN activity. Combining archival HST UV spectra with Keck/HIRES and VLT/UVES optical spectra, we estimate metallicities and physical conditions for 105 absorbers. The Cosmic Noon metallicity distribution (median []=-1.19) is statistically indistinguishable from that at z<1 (-1.18) but differs significantly from z>2.2 (-2.02). This plateau is driven by the most diffuse absorbers (16.4 at most N HI<17.2), which reach their z<1 enrichment level by Cosmic Noon, whereas denser absorbers remain more metal-poor than their z<1 counterparts and continue to be enriched at later times. Unlike at z>2.2, no absorber falls below []=-3.5, indicating no pristine CGM-like gas at Cosmic Noon. Absorbers in BRIDGE-I trace overdensities of 400 δ b 2200, higher than at z>2.2. Mean N HI differs by a factor of 400 across absorber types, but mean total hydrogen column by only 2.5, as higher N HI is offset by a higher neutral fraction. The absorber classes thus differ in ionization state and metallicity rather than the total gas content. A metallicity floor of [] about-2.0 emerges for N HI>19.0 absorbers, indicating that denser, more ISM-like gas is well mixed as a population, while more diffuse gas retains a metal-poor population that is not yet fully mixed.