The following document lists the file abstract/PPUXLEY_PJP_GAL.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
The flux of hydrogen ionizing photons is fundamental in understanding many aspects of actively star-forming galaxies, including the star formation rate, the number of massive stars and the stellar mass function. The ionization rate is conventionally measured from the flux in a hydrogen recombination line (e.g. H alpha) with the flux in a second line (e.g. H beta) used to estimate, and correct for, the attenuation due to dust. However, this method will underestimate the dust extinction if the sources of emission (HII regions) and the dust are distributed along the line of sight. To resolve this problem we have undertaken a programme of multi-wavelength spectroscopy involving optical, near-infrared and mm-wavelength recombination line observations and modelling of the radiative transfer through the inhomogeneous medium. Our results show that the assumption of purely foreground absorption can grossly underestimate the intrinsic ionization rate and that some starburst galaxies may have a significant optical depth even in the near-IR. Consequently we now wish to extend these studies to longer wavelengths and perform spectroscopy in the near- and mid-IR (4-28um) of a small sample of starburst galaxies. These observations will enable us to investigate the spatial distributions of dust and HII regions and finally determine reliable values for the intrinsic ionization rate.