Evolution of cold streams in hot gaseous haloes

Abstract

ABSTRACT In the prevailing model of galaxy formation and evolution, the process of gas accretion on to central galaxies undergoes a transition from cold-dominated to hot-dominated modes. This shift occurs when the mass of the parent dark matter haloes exceeds a critical threshold known as Mshock. Moreover, cold gas usually flows on to central galaxies through filamentary structures, currently referred to as cold streams. However, the evolution of cold streams in haloes with masses around Mshock, particularly how they are disrupted, remains unclear. To address this issue, we conduct a set of idealized hydrodynamic simulations. Our simulations show that (1) for a gas metallicity $Z=0.001{\!-\!}0.1\, \mathrm{Z}_{\odot }$, cold stream with an inflow rate $\sim 3\, {\rm {M}_{\odot }}\, \mathrm{yr}^{-1}$ per each can persist and effectively transport cold and cool gas to the central region (<0.2 virial radius) in haloes with mass $10^{12}\, {\rm {M}_{\odot }}$, but is disrupted at a radius around 0.2 virial radius due to compression heating for haloes with mass $3 \times 10^{12}\, {\rm {M}_{\odot }}$. (2) At z ∼ 2, the maximum halo mass that capable of hosting and sustaining cold streams Mstream is between 1 × 1012 M⊙ and $1.5\times 10^{12}\,\rm {{M}_{\odot }}$ for gas metallicity ${\it Z}=0.001\, \mathrm{Z}_{\odot }$, while for a higher gas metallicity ${\it Z}=0.1\, \mathrm{Z}_{\odot }$, this value increases to $\sim 1.5\times 10^{12}\,\rm {{M}_{\odot }}$. (3) The evolution and ultimate fate of cold streams are determined primarily by the rivalry between radiative cooling and compression. Stronger heating due to compression in haloes more massive than Mstream can surpass cooling and heat the gas in cold streams to the hot ($\ge 10^6\,$ K) phase.