The rate of structure formation in the Universe is different in homogeneous and clustered dark energy models. The degree of dark energy clustering depends on the magnitude of its effective sound speed c ^2_eff ≡ c e and for c e = 0 dark energy will cluster in a similar fashion to dark matter while for c e = 1 stays (approximately) homogeneous. In this paper we try to constrain the dark energy effective sound speed using current available data including SnIa, Baryon Acoustic Oscillation, CMB shift parameter (Planck and WMAP), Hubble parameter, Big Bang Nucleosynthesis and the growth rate of structures fσ 8 (z).
