Alfaro, Emilio J.; Cabrera-Lavers, A.; Giammanco, Corrado; Asensio-Ramos, A.; Cepa, J.; Bongiovanni, A.; Beckman, J. E.; Cedrés, B.
Bibliographical reference
The Astrophysical Journal Letters, Volume 765, Issue 1, article id. L24, 6 pp. (2013).
Description
Using the OSIRIS tunable narrowband imager on the 10.4 m GTC (La Palma),
we have mapped the SAB(rs)cd galaxy NGC 6946 over a ~7.3 × 7.5
arcmin2 field in the emission lines of the [S II]
λλ6717, 6731 doublet, and in Hα. From these maps we
have produced catalogs of the Hα luminosities and effective radii
of 557 H II regions across the disk, and derived the [S II] emission
line ratios of 370 of these. The Hα observations were used to
derive the mean luminosity-weighted electron densities for the regions
of the sample, while the [S II] line ratios allowed us to derive values
of the in situ electron densities in the denser zones from which the
major fraction of the radiation in these lines is emitted for 58 of the
regions. This is by far the largest data set of its kind for a single
galaxy. A classical two-phase model is used to derive the filling
factors of the regions. We find that although the mean electron density
decreases with the square root of the radius of the regions, the in situ
density is essentially independent of this radius. Thus the filling
factor falls systematically, as the radius and the luminosity of the
regions increases, with a power law of exponent -2.23 between
filling factor and radius. These measurements should enhance the
perspectives for more refined physical models of H II regions.
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