  Context. Main sequence stars with a convective core are predicted to
stochastically excite Internal Gravity Waves (IGWs), which effectively
transport angular momentum throughout the stellar interior and explain the
observed near-uniform interior rotation rates of intermediate-mass stars.
However, there are few detections of IGWs, and fewer still made using
photometry, with more detections needed to constrain numerical simulations.
Aims. We aim to formalise the detection and characterisation of IGWs in
photometric observations of stars born with convective cores (M > 1.5
M$_{\odot}$) and parameterise the low-frequency power excess caused by IGWs.
Methods. Using the most recent CoRoT light curves for a sample of O, B, A and F
stars, we parameterise the morphology of the flux contribution of IGWs in
Fourier space using an MCMC numerical scheme within a Bayesian framework. We
compare this to predictions from IGW numerical simulations and investigate how
the observed morphology changes as a function of stellar parameters. Results.
We demonstrate that a common morphology for the low-frequency power excess is
observed in early-type stars observed by CoRoT. Our study shows that a
background frequency-dependent source of astrophysical signal is common, which
we interpret as IGWs. We provide constraints on the amplitudes of IGWs and the
shape of their detected frequency spectrum across a range of mass, which is the
first ensemble study of stochastic variability in such a diverse sample of
stars. Conclusions. The evidence of a low-frequency power excess across a wide
mass range supports the interpretation of IGWs in photometry of O, B, A and F
stars. We also discuss the prospects of observing hundreds of massive stars
with the Transiting Exoplanet Survey Satellite (TESS) in the near future.
