Bradley, T. R.; Knapen, J. H.; Beckman, J. E.; Folkes, S. L.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 459, Issue 1, November III 2006, pp.L13-L16
Fecha de publicación:
11
2006
Revista
Número de citas
50
Número de citas referidas
43
Descripción
Context: .Statistical properties of H ii region populations in disk
galaxies yield important clues to the physics of massive star
formation. Aims: .We present a set of H ii region catalogues and
luminosity functions for a sample of 56 spiral galaxies in order to
derive the most general form of their luminosity function.
Methods: .H ii region luminosity functions are derived for individual
galaxies which, after photometric calibration, are summed to form a
total luminosity function comprising 17 797 H ii regions from 53
galaxies. Results: .The total luminosity function, above its lower
limit of completeness, is clearly best fitted by a double power law with
a significantly steeper slope for the high luminosity portion of the
function. This change of slope has been reported in the literature for
individual galaxies, and occurs at a luminosity of log L =
38.6±0.1 (L in erg s-1) which has been termed the
Strömgren luminosity. A steep fall off in the luminosity function
above log L = 40 is also noted, and is related to an upper limit to the
luminosities of underlying massive stellar clusters. Detailed data are
presented for the individual sample galaxies. Conclusions: .The
luminosity functions of H ii regions in spiral galaxies show a two slope
power law behaviour, with a significantly steeper slope for the high
luminosity branch. This can be modelled by assuming that the high
luminosity regions are density bounded, though the scenario is
complicated by the inhomogeneity of the ionized interstellar medium. The
break, irrespective of its origin, is of potential use as a distance
indicator for disc galaxies.