Environmental Dependence of Galactic Properties Traced by Lyα Forest Absorption: Diversity among Galaxy Populations

In order to shed light on how galactic properties depend on the intergalactic medium (IGM) environment traced by the Lyα forest, we observationally investigate the IGM-galaxy connection using the publicly available 3D IGM tomography data (CLAMATO) and several galaxy catalogs in the COSMOS field. We measure the cross-correlation function (CCF) for 570 galaxies with spec-z measurements and detect a correlation with the IGM up to 50 h^-1 comoving Mpc. We show that galaxies with stellar masses of 10⁹-10¹⁰ M_⊙ are the dominant contributor to the total CCF signal. We also investigate CCFs for several galaxy populations: Lyα emitters (LAEs), Hα emitters (HAEs), [O III] emitters (O3Es), active galactic nuclei (AGNs), and submillimeter galaxies (SMGs), and we detect the highest signal in AGNs and SMGs at large scales (r ≥ 5 h^-1 Mpc), but in LAEs at small scales (r < 5 h^-1 Mpc). We find that they live in various IGM environments—HAEs trace the IGM in a similar manner to the continuum-selected galaxies, but LAEs and O3Es tend to reside in higher-density regions. Additionally, LAEs' CCF is flat up to r ∼ 3 h^-1 Mpc, indicating that they tend to avoid the highest-density regions. For AGNs and SMGs, the CCF peak at r = 5-6 h^-1 Mpc implies that they tend to be in locally lower-density regions. We suspect that it is due to the photoionization of IGM H I by AGNs, i.e., the proximity effect.