Multi-component Decomposition of Cosmic Infrared Background Fluctuations

Abstract

The near-infrared background between 0.5 µm to 2 µm contains a wealth of information related to radiative processes in the universe. Infrared background anisotropies encode the redshift-weighted total emission over cosmic history, including any spatially diffuse and extended contributions. The anisotropy power spectrum is dominated by undetected galaxies at small angular scales and diffuse background of Galactic emission at large angular scales. In addition to these known sources, the infrared background also arises from intra-halo light (IHL) at z < 3 associated with tidally-stripped stars during galaxy mergers. Moreover, it contains information on the very first galaxies from the epoch of reionization (EoR). The EoR signal has a spectral energy distribution (SED) that goes to zero near optical wavelengths due to Lyman absorption, while other signals have spectra that vary smoothly with frequency. Due to differences in SEDs and spatial clustering, these components may be separated in a multi-wavelength-fluctuation experiment. To study the extent to which EoR fluctuations can be separated in the presence of IHL, extra-galactic and Galactic foregrounds, we develop a maximum likelihood technique that incorporates a full covariance matrix among all the frequencies at different angular scales. We apply this technique to simulated deep imaging data over a 2×100 deg 2 sky area from 0.75 µm to 5 µm in 9 bands and find that such a "frequency tomography" can successfully reconstruct both the amplitude and spectral shape for representative EoR, IHL and the foreground signals.

Revealing the formation histories of the first stars with the cosmic near-infrared background

“…We employ a semi-empirical model to describe the known galaxy population, and then add in a physically-motivated, but flexible, model for Pop III stars that allow us to explore a wide range of plausible scenarios. This, in various aspects, improves over previous models, which, e.g., parameterized the fraction of cosmic star formation in Pop III haloes as a function of redshift only and/or employed simpler Pop II models calibrated to earlier datasets (e.g., Cooray et al 2012b;FZ13;Helgason et al 2016;Feng et al 2019). These advancements not only allow more accurate modeling of the contribution to the NIRB from high-𝑧 galaxies, but also provide a convenient physical framework to analyse and interpret datasets of forthcoming NIRB surveys aiming to quantify the signal level of galaxies during and before reionization.…”

“…which is frequently adopted in the literature to estimate the Pop III contribution (e.g., Cooray et al 2012b;Fernandez & Zaroubi 2013;Feng et al 2019). It can be seen that, compared with the phenomenological description using the error function, our physical models imply a more extended early phase with the Pop II SFRD gradually catching up.…”

“…For reference, we show in Fig. 6 the remaining fluctuation signal associated with low-𝑧 (𝑧 3) galaxies after masking bright, resolved ones, as predicted by the luminosity function model from Feng et al (2019). Other sources of emission such as the IHL may also contribute a significant fraction of the total observed fluctuations -though with a lower certainty, making the component separation even more challenging.…”

“…Note that in practice the contribution of high-𝑧 star-forming galaxies will be blended with other NIRB components from lower redshifts. Separation techniques relying on the distinction in the spectral shape of each component have been demonstrated in e.g., Feng et al (2019). For reference, we show in Fig.…”

“…In particular, Fernandez and Zaroubi (2013, hereafter FZ13) point out that strong Ly𝛼 emission from Pop III stars can lead to a "bump" in the mean spectrum of the NIRB, a spectral signature that can reveal information about physical properties of Pop III stars and the timing of the Pop III to Pop II transition. The soon-to-be-launched satellite Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx;Doré et al 2014) has the raw sensitivity to detect the contribution of galaxies during the epoch of reionization (EoR) to the NIRB at high significance (Feng et al 2019), making it possible, at least in principle, to detect or rule out such spectral features. However, despite significant differences in detailed predictions, previous modeling efforts (e.g., Fernandez & Komatsu 2006;Cooray et al 2012b;Yue et al 2013a;Helgason et al 2016) have suggested that first galaxies during and before the EoR may only contribute to approximately less than 1% of both the source-subtracted NIRB mean intensity and its angular fluctuations, as measured from a series of deep imaging surveys (e.g., Kashlinsky et al 2012;Zemcov et al 2014;Seo et al 2015).…”