Dark matter merging induced turbulence as an efficient engine for gas cooling

Abstract

We have performed a cosmological numerical simulation of primordial baryonic gas collapsing onto a $3\times 10^7$M${}_{\odot }$ dark matter (DM) halo. We show that the large scale baryonic accretion process and the merger of few $\sim 10^6$ M${}_{\odot }$ DM halos, triggered by the gravitational potential of the biggest halo, is enough to create super sonic ($\mathcal{M}>10$) shocks and develop a turbulent environment. In this scenario the post shocked regions are able to produced both H${}_2$ and HD molecules very efficiently reaching maximum abundances of $n_{{\mathrm{H}}_2}\sim 10^{-2}{n}_{\mathrm{H}}$ and $n_{\mathrm{HD}}\sim \mathrm{few}\times 10^{-6}{n}_{\mathrm{H}}$, enough to cool the gas below 100K in some regions. The kinetic energy spectrum of the turbulent primordial gas is close to a Burgers spectrum, ${\hat{E}}_k\propto k^{-2}$, which could favor the formation of low mass primordial stars. The solenoidal to total kinetic energy ratio is $0.65\la R_k\la0.7$ for a wide range of wave numbers; this value is close to $R_k\approx 2/3$ natural equipartition energy value of a random turbulent flow. In this way turbulence and molecular cooling seem to work together in order to produce potential star formation regions of cold and dense gas in primordial environments. We conclude that both the mergers and the collapse process onto the main DM halo provide enough energy to develop super sonic turbulence which favor the molecular coolants formation: this mechanism, which could be universal and the main route toward formation of the first galaxies, is able to create potential star forming regions at high redshift.

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Cited by in corpus (10)

• Primordial Star Formation under the Influence of Far Ultraviolet Radiation: 1540 Cosmological Halos and the Stellar Mass Distribution
• Star Formation in the First Galaxies I: Collapse Delayed by Lyman-Werner Radiation
• Star Formation in the First Galaxies - II: Clustered Star Formation and the Influence of Metal Line Cooling
• Gas infall into atomic cooling haloes: on the formation of protogalactic disks and supermassive black holes at z > 10
• Star formation in the first galaxies - III. Formation, evolution, and characteristics of the first stellar cluster
• The role of the H${}_2$ adiabatic index in the formation of the first stars
• Dark-matter halo mergers as a fertile environment for low-mass Population III star formation
• Statistical properties of dark matter mini-haloes at z >= 15
• Over-cooled haloes at z > 10: a route to form low-mass first stars
• Star Formation for Predictive Primordial Galaxy Formation