NGC 5775: Anatomy of a disk-halo interface

We present the first high-resolution study of the disk-halo interface in an edge-on galaxy (NGC 5775) in which every component of the interstellar med ium is represented and resolved (though not all to the same resolution). Ne w single-dish CO J = 2-1 and CO J = 1-0 data, ROSAT X-ray data, and HIRES I RAS data are presented along with HI data which emphasizes the high latitud e features. In conjunction with previously published radio continuum (6 and 20 cm) and H alpha data, we find spatial correlations between various ISM components in that all components of the ISM are present in the disk-halo f eatures (except for CO for which there is insufficient spatial coverage). T he HI features extend to similar to 7 kpc above the plane, form loops in po sition-position space, in one case, form a loop in position-velocity space, and are also observed over a large velocity range. This implies that the d isk-halo features represent expanding supershells. However, the shells may be incomplete and partially open-topped, suggesting that we are observing t he breakup of the supershells as they traverse the disk-halo interface. The re is some evidence for acceleration with z and both redshifted and blueshi fted velocities are present, although the gas which is lagging with respect to galactic rotation dominates. The radio continuum spectral index is flat ter around the shell rims and we show that this cannot be due to a contribu tion from thermal gas but rather is due to intrinsic flattening of the non- thermal spectral index, suggesting that shocks may be important in these re gions. The H alpha emission is located interior to the HI. For feature F3, the H alpha emission forms the interior "skin" of the HI shell, yet there a ppears to be a minimum of in-disk star formation immediately below the feat ure. We present a picture of a "typical" HI supershell which accelerates an d breaks up through the disk-halo interface. Such a feature is likely inter nally generated via an energetic event in the disk.