Extinction in Nebular Luminosities & Star Formation Rate of Disk
  Galaxies: Inclination Correction
  Star formation is one of the most important processes in galaxy formation.
The luminosity of Halpha recombination and [OII] forbidden emissions remain to
be most used in measuring formation rate of massive stars in galaxies. Here we
report the inclination dependency of continuum-subtracted and
aperture-corrected nebular luminosities, including Halpha, Hbeta, Hgamma,
[OII], [NII], of disk-dominated galaxies in the local universe. Their
luminosities decrease by a factor of three from face-on to edge-on (axis ratio
limit = 0.17) orientations. This dependence is deduced to be caused by
extinction due to diffuse dust within the disks with an amplitude of 1.2 mag.
The line-luminosity--inclination relation provides a novel way to remove
extinction in emission lines and present star formation rate of disk galaxies
out to redshift of 1.6.
