The diffuse ionized interstellar medium perpendicular to the plane of NGC 891

Details The diffuse ionized interstellar medium perpendicular to the plane of NGC 891 The diffuse ionized interstellar medium perpendicular to the plane of NGC 891

Jul 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990nascp3084..172d&link_type=abstract

In NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers p 172-173 (SEE N91-

Computer Science

Cosmic Dust, Disk Galaxies, Galaxies, H Ii Regions, Imaging Techniques, Interstellar Matter, Ionized Gases, Milky Way Galaxy, Neutral Gases, Scattering, Star Formation, Alpha Particles, Asymmetry, Confinement, Continuums, H Alpha Line, Halos, High Energy Electrons, Hydrogen, Relativistic Particles, Scale Height

Scientific paper

In an attempt to study the structure and the properties of the diffuse ionized interstellar medium perpendicular to the plane of disk galaxies researchers obtained H alpha images and spectra of NGC 891. Perhaps the most remarkable property of the H alpha emission line in NGC 891 is its extension out of the plane of the galaxy: researchers are able to measure the H alpha line out to more than 30 seconds (1.4 kpc) from the midplane. This means that the ionized hydrogen extends at least four times higher than the neutral hydrogen layer. An anomalously large scale-height for the ionized gas of approx. equals 1 kpc is also found in the Milky Way. The echelle spectra show a changing ratio of NII to H alpha. This excludes the possibility that the large scaleheight of the emission is due to scattering of disk emission by dust high above the plane. The z-extent of the H alpha emission is confirmed by the imaging result. The large z-extent of the ionized gas is confined to the inner half of the visible disk. In this inner region the H alpha distribution also shows a filamentary structure of the diffuse ionized medium. These filaments, sticking out of the plane, originate in HII regions in the plane. The H alpha image also shows a large scale asymmetry if the NE and SW parts of the disk are compared. The NE part is more prominent and extended in H alpha. The same asymmetry is also seen in the radio continuum distribution. This correlation between the diffuse ionized medium and the distribution of relativistic electrons is one example of a relation between star formation processes in the disk and the various components of the halo. Thermal filaments or spurs which are related to HII regions are also known in the Galaxy. These filamentary structures perpendicular to the galactic planes may represent the chimneys which result in the supernova dominated model of the Interstellar Medium by Norman and Ikeuchi (1989).

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