Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aspc..331..177r&link_type=abstract
Extra-Planar Gas, ASP Conference Proceedings, Vol. 331. Edited by Robert Braun. Proceedings of the meeting held at Dwingeloo,
Astronomy and Astrophysics
Astronomy
Scientific paper
We present new results of an HST/WFPC2 investigation of the disk-halo interface in the edge-on spiral galaxy NGC 891. Our high spatial resolution F656N (Hα) observations (4.6 pc at the distance to NGC 891) reveal an extended diffuse ionized gas halo, which fills almost the entire field of view of our WFPC2 pointing. The majority of the Hα emission is diffuse. Several discrete features (e.g., filaments) are visible as well. Some of the filaments reach distances of up to 2.2 kpc above the galactic plane, and are extremely collimated, even at high galactic latitudes. Although such structures are currently not supported in theoretical models, which describe possible transport mechanisms in a general way, there is evidence that magnetic fields play a vital role. There is no clear evidence for the chimney scenario, which may partially be attributed due to dust extinction close to the galactic midplane, which complicates the situation. We also investigate extra-planar dust features, which are best visible in unsharp-masked images of our broadband F675W image, and we compare them to the spatial distribution of diffuse ionized gas filaments. The high-|z| dust is detected out to distances of 2.2 kpc above/below the galactic midplane. Individual dust features, however, are not spatially correlated with diffuse ionized gas counterparts, such as individual filaments. Quite interestingly, the orientation of the dust features changes from being mostly aligned perpendicular to the disk at low galactic latitudes, to a parallel alignment at high-|z|. We compare the diffuse ionized gas distribution to the hot ionized medium, traced by X-ray observations performed with Chandra. There exists a good correlation of the presence of the warm and hot ionized gas, in particular, an X-ray bright region at |z|˜1--1.5 kpc fills the entire northern halo region, whereas the intensity in the midplane is considerably diminished.
Dettmar Ralf-Juergen
Norman Colin A.
Rossa Joern
Walterbos Reinirus Antonius Maria
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