Physics
Scientific paper
Feb 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999noao.prop..112r&link_type=abstract
NOAO Proposal ID #1999A-0112
Physics
Scientific paper
We propose a long-term program of spectroscopic observations of extraplanar (above the HII region layer) Diffuse Ionized Gas (DIG) layers in edge-on galaxies. The motivation derives from the success of, and issues raised by, previous imaging of DIG in such galaxies, and spectroscopy of the DIG layer in NGC 891. The latter observations have led to new results such as the first real requirement for a secondary source of ionization beyond photoionization by massive disk stars, and strong evidence that the halo gas rotates more slowly than the disk gas. Hence the goal of the proposed observations is to constrain, in a larger sample, the source(s) of ionization of extraplanar DIG, its physical state, kinematics, and the variation of these within galaxies and between galaxies with different properties such as star formation rate and environment. Five edge-ons will be observed, with at least 2 slit placements (oriented perpendicular to the plane) at various positions along the major axis of each galaxy. We will observe the red lines H(alpha), [N II], [S II], [O I], and the blue lines [O III] and H(beta), from which a wealth of information can be derived. The results will constrain the broader issues of the disk-halo cycling of gas, the structure of the ISM in general, the production of extended gaseous halos around galaxies, and the escape of ionizing radiation into intergalactic space. This is a resubmission of a proposal granted four nights in Spring 1998, for which only two hours of useful data were obtained due to weather - but even these netted an interesting, promising new result for the edgeon NGC 4302. We have redesigned the strategy used for the NGC 891 spectroscopy to greatly increase the efficiency of the observing. We ask for four nights in three Spring semesters and 3 nights in one Fall semester.
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