We present a steady-state analytical model for pressure-regulated formation of molecular clouds (MC) and stars (SF) in gaseous galactic disks and apply it to the Milky Way (MW). MC formation depends on midplane interstellar pressure P₈ₒ₌ and metallicity Z, and for galactocentric distances R5 kpc, P₈ₒ₌ (R) scales approximately linearly with molecular gas surface density Σ ₌₎₋ (R). The molecularization of the cold neutral medium (CNM) is due to the opacity of small dust grains that protect the center of the cloud from dissociating radiation when the column density is Σd 5\ (Z_/Z) M_ pc^-2. The H₂ formation rate per hydrogen atom is F10^-15 (P₈ₒ₌/P_) T₁₀₀^-1/2s^-1, and the corresponding formation rate per unit area is Σ^+ ₌₎₋ 510^-2 (P₈ₒ₌/P_) T₁₀₀^-1/2M_~kpc^-2~yr^-1, where P_ is the pressure at the solar circle and T₁₀₀=T/100 K is the temperature of the cloud. In equilibrium, this equals the molecular gas destruction rate Σ^- ₌₎₋ due to SF. Self-gravity sets in when the column density of a cloud reaches Σ ₒ₆=Σ ₒ₆, (P₈ₒ₌/P_) ^1/2, with Σ ₒ₆, 30\ M_\ pc^-2. Given the distribution of P₈ₒ₌ (R) and Z (R) in the MW, the SF process at 5 R11 kpc follows a two-step track: first, MCs form from CNM gas and then they form stars when self-gravity sets in. The resulting SFR surface density is ΣSFR (R) (1. 6-4) 10^-3 (P₈ₒ₌/P_) \ M_~ kpc^-2yr^-1 with an average final SF efficiency of ε ₒ₅ (3-8) 10^-2.
Franco et al. (Mon,) studied this question.