Extinction in Nebular Luminosities & Star Formation Rate of Disk Galaxies: Inclination Correction

TL;DR

This paper investigates how the observed nebular luminosities and star formation rates in disk galaxies are affected by galaxy inclination, revealing a significant extinction effect that can be corrected for more accurate measurements.

Contribution

It introduces a new inclination correction method for nebular emission lines, improving star formation rate estimates in disk galaxies up to redshift 1.6.

Findings

Luminosities decrease by a factor of three from face-on to edge-on orientations.

Diffuse dust causes an extinction of about 1.2 mag.

The inclination relation enables extinction correction for emission lines.

Abstract

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.