Star formation at high redshift
  We present here a three-dimesional hydrodynamical simulation for star
formation. Our aim is to explore the effect of the metal-line cooling on the
thermodynamics of the star-formation process. We explore the effect of changing
the metallicty of the gas from $Z/Z_{\odot}=10^{-4}$ to $Z/Z_{\odot}=10^{-2}$.
Furthermore, we explore the implications of using the observational abundance
pattern of a CEMP-no star, which have been considered to be the missing
second-generation stars, the so-called Pop. III.2 stars. In order to pursue our
aim, we modelled the microphysics by employing the public astrochemistry
package KROME, using a chemical network which includes sixteen chemical species
(H, H$^{+}$, H$^{-}$, He, He$^{+}$, He$^{++}$, e$^{-}$, H$_{2}$, H$_{2}^{+}$,
C, C$^{+}$, O, O$^{+}$, Si, Si$^{+}$, and Si$^{++}$). We couple KROME with the
fully three-dimensional Smoothed-particle hydrodynamics (SPH) code GRADSPH.
With this framework we investigate the collapse of a metal-enhanced cloud,
exploring the fragmentation process and the formation of stars. We found that
the metallicity has a clear impact on the thermodynamics of the collapse,
allowing the cloud to reach the CMB temperature floor for a metallicity
$Z/Z_{\odot}=10^{-2}$, which is in agreement with previous work. Moreover, we
found that adopting the abundance pattern given by the star SMSS
J031300.36-670839.3 the thermodynamics behavior is very similar to simulations
with a metallicity of $Z/Z_{\odot}=10^{-2}$, due to the high carbon abundance.
As long as only metal line cooling is considered, our results support the
metallicity threshold proposed by previous works, which will very likely
regulate the first episode of fragmentation and potentially determine the
masses of the resulting star clusters.
