Galaxy inclination and the IRX-beta relation: Effects on UV
  star-formation rate measurements at intermediate to high redshifts
  At intermediate and high redshifts, measurements of galaxy star-formation
rates are usually based on rest-frame ultraviolet (UV) data. A correction for
dust attenuation, A_UV, is needed for these measurements. This correction is
typically inferred from UV spectral slopes (beta) using an equation known as
"Meurer's Relation." In this paper, we study this relation at a redshift of 1.5
using images and photometric measurements in the rest-frame UV (HST) through
mid-infrared (Spitzer). It is shown that massive star-forming galaxies (above
10^10 Msun) have dust corrections that are dependent on their inclination to
the line-of-sight. Edge-on galaxies have higher A_UV and infrared excess
(IRX=L(IR)/L(UV)) than face-on galaxies at a given beta. Interestingly, dust
corrections for low-mass star-forming galaxies do not depend on inclination.
This is likely because more massive galaxies have more disk-like
shapes/kinematics, while low-mass galaxies are more prolate and have more
disturbed kinematics. To account for an inclination-dependent dust correction,
a modified Meurer's Relation is derived: A_UV=4.43+1.99 beta - 1.73 (b/a-0.67),
where b/a is the galaxy axis ratio. This inclination-dependence of A_UV can be
explained by a two-component model of the dust distribution inside galaxies. In
such a model, the dust attenuation of edge-on galaxies has a higher
contribution from a "mixture" component (dust uniformly mixed with stars in the
diffuse interstellar medium), and a lower contribution from a "birth cloud"
component (near-spherical dust shells surrounding young stars in H II regions)
than that of face-on galaxies. The difference is caused by the larger
path-lengths through disks at higher inclinations.
