tokens: nearby neighbors or from morphologically different galaxies. If we ignore the contamination (which is significant), the SFR efficiencies determined in Section 3.2.3 would be increased by a factor of about two. This sets an upper limit on the any potential biases in sample selection on the radial surface brightness and the resultant SFR efficiencies. 2.5. Effects of Ly<italic>α</italic> on the Surface Brightness Profiles The Ly α emission line falls into the rest-frame FUV bandpass and could potentially contaminate the measured flux. We consider whether Ly α could be contaminating our stacks, and thereby the resulting surface brightness profiles. Previously, Rafelski et al. ( 2011 ) conducted a test to see whether a typical SFG Ly α line would significantly affect the measured photometry by using the stacked LBG spectrum from Shapley et al. ( 2003 ) to estimate the effect, and found it to be negligible. However, it is possible that a subset of our sample has much stronger Ly α emission than a typical LBG, such as the green peas (Henry et al. 2015 ), which could bias the SFRs obtained from the rest-frame FUV continuum high. To test for this possibility, in particular in the galaxy outskirts, we conduct the following tests. First, for the and samples we create a smaller sample including about half of the galaxies for which Ly α does not fall in the FUV bandpass by constraining the redshift, and compare the radial surface brightness profile of that stack to the full subsample stacks. We find no evidence of a decrease in the flux in the outskirts of the galaxies within their uncertainties. Second, we compare the radial surface brightness profiles for the FUV and NUV bands, since the NUV bands will not include the Ly α line. Again, we find no evidence of a change in the radial surface brightness profile in the outskirts. The fact that the galaxies have the same radial surface brightness profile shapes in both bands suggests that the Ly α line has little to no effect on the radial surface brightness profiles. We note that this is not in conflict with the results by Steidel et al. ( 2011 ), who find extended Ly α halos around SFGs. First, that study samples a different galaxy population of brighter SFGs. Second, the Steidel et al. ( 2011 ) study goes out to ∼80 kpc using ground-based observations, while we limit ourselves to the central ∼10 kpc, which is barely resolved in that ground-based study. Third, Steidel et al. ( 2011 ) use narrowband filters to find the Ly α , while our stacks are in very broad filters, and thus the Ly α would not contribute except in the extreme emitter cases, and then only in the FUV bands for part of the redshift range. 3. SFR EFFICIENCY The radial surface brightness profiles of the SFGs show spatially extended star formation in the galaxy outskirts. Star formation is expected in the outskirts of high-redshift galaxies, as it is measured in atomic-dominated hydrogen gas at low redshift (Thilker et al. 2007 ; Boissier et
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