From larger-scale cold-gas angular-momentum environment to galaxy star-formation activeness

Abstract

We study the influence of the ambient large-scale cold-gas vorticity on the specific star formation rate (sSFR) of central galaxies with stellar masses of $10.0<\log\,M_{\ast}/\mathrm{M_{\odot}}<11.5$ at $z=0$, using the TNG100 simulation. The cold-gas vorticity defined and calculated for gas with $T_{\rm gas} < 2\times 10^4 \mathrm{K}$ and on scales of $\sim$ 1 Mpc can well describe the angular motion of the ambient cold gas. We find crucial evidence for connections between the cold-gas vorticity and star-formation activeness, such that at any given halo mass (particularly below $10^{13}\,\mathrm{M_{\odot}}$), galaxies living in higher cold-gas vorticity environments are generally less star-forming, regardless of their large-scale environment types (filament or knot), or star formation states (star-forming or quenched). Specifically, at a fixed halo mass scale of $10^{12}-10^{13}\,\mathrm{M_{\odot}}$, the median sSFR of galaxies living in environments with the top 30\% cold-gas vorticity is $\sim 0.5$ dex below that of galaxies living in environments with the bottom 30\% cold-gas vorticity. At any fixed halo mass scale, cold-gas vorticities around filament galaxies are generally higher than those around knot galaxies, consistent with that filament galaxies have lower sSFRs than knot galaxies. This large-scale cold-gas vorticity is highly connected to the orbital angular momentum of neighboring galaxies up to a distance of $\sim$ 500 kpcs, indicating their common origin and a possible angular momentum inheritance/modulation from the latter to the former. The negative modulation by the environmental vorticity to galaxy star formation is only significantly observed for the cold gas, indicating the unique role of cold-gas angular momentum.