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We use spectral stacking to measure the contribution of galaxies of differentmasses and in different hierarchies to the cosmic atomic hydrogen (HI) massdensity in the local Universe. Our sample includes 1793 galaxies at $z < 0.11$observed with the Westerbork Synthesis Radio Telescope, for which Sloan DigitalSky Survey spectroscopy and hierarchy information are also available. We find acosmic HI mass density of $\Omega_{\rm HI} = (3.99 \pm 0.54)\times 10^{-4}h_{70}^{-1}$ at $\langle z\rangle = 0.065$. For the central and satellitegalaxies, we obtain $\Omega_{\rm HI}$ of $(3.51 \pm 0.49)\times 10^{-4}h_{70}^{-1}$ and $(0.90 \pm 0.16)\times 10^{-4} h_{70}^{-1}$, respectively. Weshow that galaxies above and below stellar masses of $\sim$10$^{9.3}$M$_{\odot}$ contribute in roughly equal measure to the global value of$\Omega_{\rm HI}$. While consistent with estimates based on targeted HIsurveys, our results are in tension with previous theoretical work. We showthat these differences are, at least partly, due to the empirical recipe usedto set the partition between atomic and molecular hydrogen in semi-analyticalmodels. Moreover, comparing our measurements with the cosmologicalsemi-analytic models of galaxy formation {\sc Shark} and GALFORM revealsgradual stripping of gas via ram pressure works better to fully reproduce theproperties of satellite galaxies in our sample, than strangulation. Ourfindings highlight the power of this approach in constraining theoreticalmodels, and confirm the non-negligible contribution of massive galaxies to theHI mass budget of the local Universe.

The cosmic atomic hydrogen mass density as a function of mass and galaxy hierarchy from spectral stacking