Connecting the Cosmic Star Formation Rate with the Local Star Formation

Abstract

We present a model that unifies the cosmic star formation rate (CSFR), obtained through the hierarchical structure formation scenario, with the (Galactic) local star formation rate (SFR). It is possible to use the SFR to generate a CSFR mapping through the density probability distribution functions (PDFs) commonly used to study the role of turbulence in the star-forming regions of the Galaxy. We obtain a consistent mapping from redshift $z\sim 20$ up to the present ($z=0$). Our results show that the turbulence exhibits a dual character, providing high values for the star formation efficiency ($⟨\epsilon ⟩\sim 0.32$) in the redshift interval $z\sim 3.5-20$ and reducing its value to $⟨\epsilon ⟩=0.021$ at $z=0$. The value of the Mach number (${\mathcal{M}}_{\mathrm{crit}}$), from which $⟨\epsilon ⟩$ rapidly decreases, is dependent on both the polytropic index ($\Gamma$) and the minimum density contrast of the gas. We also derive Larson's first law associated with the velocity dispersion ($⟨V_{\mathrm{rms}}⟩$) in the local star formation regions. Our model shows good agreement with Larson's law in the $\sim 10-50\mathrm{pc}$ range, providing typical temperatures $T_0\sim 10-80\mathrm{K}$ for the gas associated with star formation. As a consequence, dark matter halos of great mass could contain a number of halos of much smaller mass, and be able to form structures similar to globular clusters. Thus, Larson's law emerges as a result of the very formation of large-scale structures, which in turn would allow the formation of galactic systems, including our Galaxy.

ApJ accepted

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