Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aj....128..662t&link_type=abstract
The Astronomical Journal, Volume 128, Issue 2, pp. 662-673.
Astronomy and Astrophysics
Astronomy
15
Ism: Dust, Extinction, Galaxies: Individual (Ngc 4217), Galaxies: Ism, Galaxies: Spiral, Ism: Clouds
Scientific paper
We present high-resolution (~ 0.1") B, V, and I images of the edge-on Sb galaxy NGC 4217 obtained with the Wide Field Planetary Camera 2 (WFPC2) on-board the Hubble Space Telescope (HST). We make use of these images to study extraplanar (z>0.4 kpc) dust structures visible in absorption against the background stellar light of the galaxy, similar to those observed previously in NGC 891 and other spiral galaxies by Howk & Savage. The HST images of NGC 4217 reveal extensive high-z dust to both sides of its midplane. The dust structures have a range of morphologies, and some of the more tenuous features are traceable to heights ~2 kpc from the midplane. We investigate the physical properties of 12 individual features. We measure the apparent optical extinctions of the features and use these to infer the hydrogen column densities and masses of the structures. The extraplanar dust structures in NGC 4217 typically have NH>~4×1020 cm-2, with associated gas masses estimated to be >~2×105 Msolar, assuming Milky Way gas-to-dust relationships apply to this spiral galaxy. The energy requirements for the expulsion of such massive structures into the lower halo are large; the gravitational potential energies of similar individual structures in NGC 891 (>1052 ergs) represent the energy input of at least tens of supernovae. The morphologies of some of the extraplanar dust structures in NGC 4217 suggest supernova-driven galactic fountain or chimney phenomena may be responsible for their production. Other features at high-z are not readily linked to energetic processes in the disk.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
Howk Jay Christopher
Savage Blair. D.
Thompson Thomas W. J.
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