Cosmic Infrared Background from Early Epochs - Searching for Signatures of the First Stars

Cosmic infrared background (CIB) contains emission from epochs inaccessible to current telescopic studies, such as the era of the first stars. We discuss theoretical expectations for the CIB contributions from the early population of massive stars. We then present the latest results from the ongoing project by our team [9, 10, 11, 12] to measure/constrain CIB fluctuations from early epochs using deep Spitzer data. The results show the existence of significant CIB fluctuations at the IRAC wavelengths (3.6 to 8 μm) which remain after removing galaxies down to very faint levels. These fluctuations must arise from populations that have a significant clustering component, but only low levels of the shot noise. Furthermore, there are no correlations between the source-subtracted IRAC maps and the corresponding fields observed with the HST ACS at optical wavelengths. Taken together, these data imply that 1) the sources producing the CIB fluctuations are individually faint with Sν < a few nJy at 3.6 and 4.5 μm; 2) are located within the first 0.7Gyr (unless these fluctuations can somehow be produced by so far unobserved local galaxies of extremely low luminosity and with the unusual for local populations clustering pattern), 3) they produce contribution to the net CIB flux of at least 1-2 nW/m2/sr at 3.6 and 4.5 μm and must have mass-to-light ratio significantly below the present-day populations, and 4) they have angular density of ∼ a few per arcsec2 and are in the confusion of the present day instruments, but can be individually observable with JWST.