Attenuation law of normal disc galaxies with clumpy distributions of stars and dust

Akio K. Inoue*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

51 Citations (Scopus)


We investigate the attenuation law seen through an interstellar medium (ISM) with clumpy spatial distributions of stars and dust. The dumpiness of the dust distribution is introduced by a multiphase ISM model. We solve a set of radiative transfer equations with multiple anisotropic scatterings through the clumpy ISM in a one-dimensional plane-parallel geometry by using the mega-grain approximation, in which dusty clumps are regarded as very large particles (i.e. mega-grains). The dumpiness of the stellar distribution is introduced by the youngest stars embedded in the clumps. We assume a smooth spatial distribution for older stars. The youngest stars are surrounded by denser dusty gas and suffer stronger attenuation than diffuse older stars (i.e. age-selective attenuation). The apparent attenuation law is a composite of the attenuation laws for the clumpy younger stars and for the diffuse older stars with a luminosity weight. In general, the stellar population dominating the luminosity changes from older stars to younger stars as the wavelength decreases. This makes the attenuation law steep; the composite attenuation rapidly increases from small attenuation for older stars at a long wavelength to large attenuation for younger stars at a short wavelength. The resultant attenuation law of normal disc galaxies is expected to be much steeper than that of starburst galaxies observed by Calzetti et al. Finally, the Calzetti attenuation law is regarded as a special case with a large density in our framework.

Original languageEnglish
Pages (from-to)171-182
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 2005 May 1
Externally publishedYes


  • Dust, extinction
  • Galaxies: ISM
  • Galaxies: spiral
  • ISM: structure
  • Radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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