10.2.2 Background Estimates

When we were calculating the background levels for MIPS wavelengths in §9.5.1, we also made estimates for IRAC wavelengths. See Table 9.1 for the results. The nebula is nowhere near as bright in these wavelengths as it was for MIPS, so it is not as big a concern. Relying on Spot's estimates is better than going to IRSKY in this case, particularly because these wavelengths are all shorter than the IRAS wavelengths. For comparison to saturation limits, we need to convert the background estimates to mJy/px using IRAC pixel sizes and the conversions from Appendix A; we get $3.4\times10^{-11}$ sr/px. We note that the contribution from the background alone will not saturate the detectors, but it will eat up dynamic range, leaving less room for counts due to objects. Now, we need a better estimate of counts due to the objects.