An exaggerated schematic displaying the degeneracy in emission spectra of galaxies. In the top panel, an inflowing component in front of the galaxy appears as a component redshifted from the disk component in the spectrum. In the bottom panel, an outflowing component behind the galaxy similarly appears as a redshifted component. Though the Hα emission is similar, the Hβ emission will be more affected by extinction due to dust in the galaxy. Therefore, the Balmer decrement will reveal which component is inflowing and which is outflowing.