Cooling and fragmentation of gas in rotating protogalaxies

The dynamical, thermal, and chemical evolution of gas in protogalaxies with non-zero angular momentum is considered. It is shown that, in protogalaxies with a total mass (dark and baryonic) of M = 10⁷ M⊙ at redshifts z = 12 whose gas has rotational angular momentum (spin parameter λ ≳ 0.005), a disk-like structure forms during the initial collapse of the galaxy, in contrast to non-rotating protogalaxies, whose collapse is spherically symmetric. The existence of initial angular momentumfor gas in protogalaxies increases the cooling time of the gas, delaying the formation of the first stars. Increasing the rotational angular momentum of the gas leads to cooling of the gas to lower temperatures (T < 100 K), at which HD molecules dominate in the cooling, while the total mass of cool gas (T < 1000 K) is decreased. The stability of disk-like structures in the central regions of protogalaxies is analyzed. It is shown that the disk that is formed is gravitationally unstable, and multiple fragmentation at various distances from the center is possible when the initial rotational angular momentum of the protogalaxy is increased. The possible birth of several stars in the first protogalaxies is discussed.