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.
Instrument
SWS02
Temporal Coverage
1996-07-30T09:04:06Z/1997-01-07T10:33:35Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, PUXLEY et al., 1999, 'MID-IR RECOMBINATION LINE SPECTROSCOPY OF BRIGHT GALAXIES', 1.0, European Space Agency, https://doi.org/10.5270/esa-vxntty1
