Published online by Cambridge University Press: 25 May 2015
Given a mixed Hodge module  $\mathcal{N}$ and a meromorphic function
$\mathcal{N}$ and a meromorphic function  $f$ on a complex manifold, we associate to these data a filtration (the irregular Hodge filtration) on the exponentially twisted holonomic module
$f$ on a complex manifold, we associate to these data a filtration (the irregular Hodge filtration) on the exponentially twisted holonomic module  $\mathcal{N}\otimes \mathcal{E}^{f}$, which extends the construction of Esnault et al. (
$\mathcal{N}\otimes \mathcal{E}^{f}$, which extends the construction of Esnault et al. ( $E_{1}$-degeneration of the irregular Hodge filtration (with an appendix by Saito), J. reine angew. Math. (2015),doi:10.1515/crelle-2014-0118). We show the strictness of the push-forward filtered
$E_{1}$-degeneration of the irregular Hodge filtration (with an appendix by Saito), J. reine angew. Math. (2015),doi:10.1515/crelle-2014-0118). We show the strictness of the push-forward filtered  ${\mathcal{D}}$-module through any projective morphism
${\mathcal{D}}$-module through any projective morphism  ${\it\pi}:X\rightarrow Y$, by using the theory of mixed twistor
${\it\pi}:X\rightarrow Y$, by using the theory of mixed twistor  ${\mathcal{D}}$-modules of Mochizuki. We consider the example of the rescaling of a regular function
${\mathcal{D}}$-modules of Mochizuki. We consider the example of the rescaling of a regular function  $f$, which leads to an expression of the irregular Hodge filtration of the Laplace transform of the Gauss–Manin systems of
$f$, which leads to an expression of the irregular Hodge filtration of the Laplace transform of the Gauss–Manin systems of  $f$ in terms of the Harder–Narasimhan filtration of the Kontsevich bundles associated with
$f$ in terms of the Harder–Narasimhan filtration of the Kontsevich bundles associated with  $f$.
$f$.