  We focus on exploring the metal enrichment of the intergalactic medium (IGM)
in Cold and Warm (1.5 and 3 keV) Dark Matter (DM) cosmologies, and the
constraints this yields on the DM particle mass, using a semi-analytic model,
Delphi, that jointly tracks the Dark Matter and baryonic assembly of galaxies
at $z \simeq 4-20$ including both Supernova and (a range of) reionization
feedback (models). We find that while ${\rm M_{UV}} \geq -15$ galaxies
contribute half of all IGM metals in the Cold Dark Matter model by $z \simeq
4.5$, given the suppression of low-mass halos, larger halos with ${\rm M_{UV}}
\leq -15$ provide about 80\% of the IGM metal budget in 1.5 keV Warm Dark
Matter models using two different models for the metallicity of the
interstellar medium. Our results also show that the only models compatible with
two different high-redshift data sets, provided by the evolving Ultra-Violet
luminosity function at $z \simeq 6-10$ and IGM metal density (e.g. Simcoe et
al. 2011), are standard Cold Dark Matter and 3 keV Warm DM that do not include
any reionization feedback; a combination of the UV LF and the Diaz et al.
(2016) points provides a weaker constraint, allowing Cold and 3 keV and 1.5 keV
Warm DM models with SN feedback only, as well as CDM with complete gas
suppression of all halos with $v_{circ} \leq 30\, {\rm km\, s^{-1}}$.
Tightening the error bars on the IGM metal enrichment, future observations, at
$z \geq 5.5$, could therefore represent an alternative way of shedding light on
the nature of Dark Matter.
