tokens: rows show the correlations and S/Ns after flipping the 185 MHz image about its vertical axis before the correlation calculation, giving an independent estimate of the noise. A significant correlation between 185 MHz and 4.5 μ m sources appears after masking infrared sources down to 1 mJy, which we show in Figure 5 cleanly removes the stars from the sample. The 185 MHz and 850 nm sources exhibit a marginal correlation after masking down to 1 mJy, though it does not appear significant in comparison to the noise correlation seen after flipping the radio image. We show in Figure 7 that this is due to increased stellar contamination at 850 nm compared to that at 4.5 μ m. The 185 MHz and 4.5 μ m catalogs exhibit a positive correlation peaking at 0.0332 ± 0.005 after masking infrared sources down to 10 −4 Jy (18.9 mag) and radio sources down to 1 Jy, and remain significant down to the completeness limits of these catalogs. There is no significant correlation detection after flipping the 185 MHz image, indicating that this detection is not an artifact of the analysis or of primary beam or vignetting effects. The 185 MHz and 850 nm catalogs exhibit a marginal correlation after masking infrared sources down to 10 −3 Jy (16.4 mag) and radio sources down to 0.3 Jy, though it does not appear significant in comparison to the level of correlation noise in the flipped image. To understand these findings, we begin by investigating which 4.5 μ m sources are responsible for this correlation. We select the subset of sources detected in the WISE 3.4 μ m, 4.5 μ m, and 12 μ m bands and plot them (Figure 5 , left panel) in the [4.6 μ m]–[12 μ m] versus [3.4 μ m]–[4.6 μ m] color–color space used by Wright et al. ( 2010 ) to illustrate the separation between different types of sources. Nikutta et al. ( 2014 ) study more quantitatively how sources separate in this space, finding that stars are isolated in the region , (1 σ ). In the right panel, we plot the faintest 90% of sources (fainter than 18.25 mag at 4.6 μ m) in the same color–color space and observe that this cut effectively cleanly excludes nearly all the stars. This explains the detection of a 185 MHz–4.5 μ m correlation only after masking the brightest 10% of sources. Figure 5. The ALLWISE sources are plotted in the color–color space of Wright et al. ( 2010 ) prior to any flux cuts (left panel), showing a cluster of stars near (0, 0). The color bar shows the number of sources in each cell. Then after cutting out the brightest 10% of sources (fainter than 18.25 AB mag), the stars are cleanly removed. We roughly split the remaining sources into AGNs () and SF galaxies (; Mingo et al. 2016 ), where [3.4 μ m]—[4.6 μ m]. To further probe which mid-infrared sources are responsible for this correlation, we make a rough cut to separate quasars and active galactic nuclei (AGNs; ) from star-forming (SF) galaxies (; Mingo et al. 2016 ). In Figure 6 we plot the power spectrum of 185 MHz sources (left panel), 4.5 μ m
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