Optical and X-Ray Observations of Extraplanar Gas in the Edge-On Spiral Galaxy NGC 891
Abstract
We obtained images and spectra of NGC 891 at both X-ray and optical (Hα ) wavelengths in order to investigate properties of extraplanar gas in an edge-on spiral galaxy believed to be similar to the Milky Way. These observations are compared to the predictions of galactic fountain theory. Imaging in Hα of the NE side of NGC 891 reveals diffuse emission-line extraplanar gas (peak brightness of 24.9 mag/sq. arcsec) that is well modeled by a truncated disk of constant emission measure. Long slit spectroscopy of the Hα line within 2.4 kpc of the galaxy's plane shows that some of this emission-line gas is not corotating with the disk of the galaxy, perhaps indicating that filamentary structures seen above and below the galaxy's plane are the remnants of superbubble breakouts. The departures from corotation range up to 40 km/s. ROSAT PSPC observations show diffuse X-ray emission surrounding the disk and extending to a height above the midplane of about 2.4 kpc, which is similar to the extent of Hα and radio continuum emission. The X-ray emission is best modeled as a two temperature system with a hard (>3 keV) and a soft (0.2--0.4 keV) component. The temperature, density, scale height (6.9 kpc), and luminosity (0.5--1 times 10(40) erg/s) of the soft component are consistent with emission from a galactic fountain driven by disk supernovae. This material is based upon work supported under a National Science Foundation Graduate Fellowship and by NASA.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1992
- Bibcode:
- 1992AAS...181.4912P