Using a high quality continuum-subtracted
H image of the grand-design spiral
NGC 3359, we have catalogued a total of 547 HII
regions. The catalogue include positions, radii and
H fluxes of all HII
regions. Tables containing all these data are available through CDS or
directly from the authors.
The slope of the LF agrees broadly with slopes for other galaxies
of comparable morphological types.
We have found a change in slope in the LF of the HII
regions of NGC 3359 that occurs at a luminosity close to that
found in other galaxies of the same morphological type.
The integrated distribution function of the diameters can be well
fitted by a exponential function for the galaxy analyzed. The value of
the characteristic diameter lies within the range reported previously
in the literature for galaxies of similar morphological types.
The characteristic scale size of the HII regions of
a galaxy depends on the absolute luminosity of the galaxy; it is
larger for more luminous galaxies (Hodge 1987). The result for
NGC 3359 agrees with the fit presented by Hodge.
The largest fraction of ionized gas is found along the arms and in
a set of high brightness star formation region on the bar. There is
also a significant component of diffuse emission throughout the entire
disc. The scale length in H is 2.3
The U-I map defines the detailed locations of SF. In this colour
map we can see elongated segments of SF together "hot spots" which
compose each segment, divided by the dust, because the I-K image shows
most clearly a spiral delineated by the strong dust lanes running
along the arms.
The analysis of the K image confirms its symmetry; this indicates
that the overall morphology observed in the NIR is dominated by a
global density wave. This is not so clear in the
H image: the SF is occurring in a more
The densities, filling factors, masses, and ionization indices
derived from the luminosities and sizes of a selected set of
representative HII regions, through the range of
observed luminosities for NGC 3359, are in agreement with those
found in the previous literature on extragalactic HII
The electron densities encountered are moderately low, with values
always less than 10 cm-3, of the order of mean interstellar
number densities in galaxies.
The diffuse flux from the ISM of NGC 3359 has been calculated
by three methods to avoid the observational problems inherent in
observing any galaxy projected in a plane and due to crowding effects.
We have found that the diffuse flux in
H is a high fraction, between 20%-30%
With the assumption that the most luminous HII
regions, those with erg
s-1, are density bounded, they are likely to be the main
ionizing sources of the interstellar medium, since the calculated
leak-out of Lyc photons from these HII regions is
enough to ionize the diffuse medium in this galaxy. This excess is
especially important here since a significant fraction of these
photons will not be absorbed within the galaxy and must escape into
the intergalactic medium.