Asymmetry Revisited: The Effect of Dust Attenuation and Galaxy
  Inclination
  Dust attenuation of an inclined galaxy can cause additional asymmetries in
observations, even if the galaxy has a perfectly symmetric structure. {Taking
advantage of the integral field spectroscopic data observed by the SDSS-IV
MaNGA survey, we investigate the asymmetries of the emission-line and continuum
maps of star-forming disk galaxies.} We define new parameters, $A_a$ and $A_b$,
to estimate the asymmetries of a galaxy about its major and minor axes,
respectively. Comparing $A_a$ and $A_b$ in different inclination bins, we
attempt to detect the asymmetries caused by dust. For the continuum images, we
find that $A_a$ increases with the inclination, while the $A_b$ is a constant
as inclination changes. Similar trends are found for $g-r$, $g-i$ and $r-i$
color images. The dependence of the asymmetry on inclination suggests a thin
dust layer with a scale height smaller than the stellar populations. For the
H$\alpha$ and H$\beta$ images, neither $A_a$ nor $A_b$ shows a significant
correlation with inclination. Also, we do not find any significant dependence
of the asymmetry of $E(B-V)_g$ on inclination, implying that the dust in the
thick disk component is not significant. Compared to the SKIRT simulation, the
results suggest that the thin dust disk has an optical depth $\tau_V\sim0.2$.
This is the first time that the asymmetries caused by the dust attenuation and
the inclination are probed statistically with a large sample. Our results
indicate that the combination of the dust attenuation and the inclination
effects is a potential indicator of the 3D disk orientation.
