Evidence for a transition of the baryon cycle of galaxies at 10^9 M⊙ from the f_HI sequence and MZR

The observations of the Dark Energy Spectroscopic Instrument are generating a powerful new data set to study galaxy evolution. Using the DESI Survey Year 1 observations combined with archival data from the ALFALFA survey we jointly constrain the atomic gas sequence (M* vs. f_HI) and mass-metallicity relation (M* vs. 12 + log{O/H}) over 5 orders of magnitude in stellar mass (10^6.5 to 10^11.5 M⊙). We find a slope change of the atomic gas sequence at a stellar mass of ~10^9 M⊙. This slope change is also imprinted onto the shape and scatter of the MZR. The mass scale of the slope change is consistent with a predicted escape velocity threshold below which low mass galaxies experience significant supernova driven gas loss (Dekel & Silk 1986), as well as the possible early transition from "cold-mode" to "hot-mode" gas accretion onto dark matter haloes (e.g. Kereš et al. 2005). This is compelling evidence that there is a transition of the dominant processes regulating the evolution of dwarfs and massive galaxies, respectively.