The ΛCDM limit of the generalized Chaplygin gas scenario

We explicitly demonstrate that, contrary to recent claims, the dynamics of a generalized Chaplygin gas model with an equation of state p = −C (where C is a positive constant) is equivalent to that of a standard ΛCDM model to first order in the metric perturbations. We further argue that the analogy between the two models goes well beyond linear theory and conclude that they cannot be distinguished based on gravity alone.