NGC 891 CO(1-0) datacubes

We mapped two 6kpcx6kpc regions on the northeastern side and the area surrounding the galactic center. We apply a careful method to estimate and remove the residual contribution of the error beam to the CO cube. The vertical extent of the molecular gas is best described by a two-component Gaussian fit, consisting of a bright thin disk component (deconvolved FWHM<=360pc; upper limit) and a fainter thick disk component (deconvolved FWHM=~1.1kpc).

Statistically significant (>3{sigma}) CO(2-1) emission is detected up to 1.3-1.4kpc above the disk midplane. We estimate that the thick molecular disk component contains up to ~27% of the total molecular gas mass of the galaxy. The vertical extent of H{alpha} emission is similar to that of the molecular gas, whereas HI extends much further.

Our results demonstrate that SF-driven feedback in a non-starburst galaxy can lift significant amounts of molecular gas to large vertical distances. We interpret the presence of extraplanar molecular gas in NGC 891 in the framework of a galactic fountain scenario, in which material is expelled from star-forming regions and transported toward the outer halo. This is supported by optical images where dust columns rise from the inner disk, showing spatial correlation between CO(2-1), H{alpha}, and dust.