Looking at cosmic near-infrared background radiation anisotropies

Abstract

The cosmic infrared background (CIB) contains emissions accumulated over the entire history of the Universe, including from objects inaccessible to individual telescopic studies. The near-IR (∼ 1 − 10 µm) part of the CIB, and its fluctuations, reflects emissions from nucleosynthetic sources and gravitationally accreting black holes (BHs). If known galaxies are removed to sufficient depths the source-subtracted CIB fluctuations at near-IR can reveal sources present in the first-stars-era and possibly new stellar populations at more recent times. This review discusses the recent progress in this newly emerging field which identified, with new data and methodology, significant source-subtracted CIB fluctuations substantially in excess of what can be produced by remaining known galaxies. The CIB fluctuations further appear coherent with unresolved cosmic X-ray background (CXB) indicating a very high fraction of BHs among the new sources producing the CIB fluctuations. These observations have led to intensive theoretical efforts to explain the measurements and their properties. While current experimental configurations have limitations in decisively probing these theories, their potentially remarkable implications will be tested in the upcoming CIB measurements with the ESA's Euclid dark energy mission. We describe the goals and methodologies of LIBRAE (Looking at Infrared Background Radiation with Euclid), a NASA-selected project for CIB science with Euclid, which has the potential for transforming the field into a new area of precision cosmology. * Alexander. Kashlinsky@nasa.gov; Code 665, Observational Cosmology Lab, E. Probing IGM at pre-reionization: CMB-CIB crosspower 48 F. History of emissions from Lyman tomography 49 G. Probing BAOs and dark energy at 10 < z < 16 50 H. LIBRAE summary 51 VIII. Other forthcoming experimental configurations 52 IX. Outlook for the future 53 X. Appendix: acronyms and abbreviations 54 XI. Acknowledgments 54 References 55 4π c I ν /h Planck = 0.63 Iν MJy/sr cm −3 . For comparison the CMB photons are orders-of-magnitude more abundant with n CMB = 413 cm −3 .CMB observations established the flat geometry of the Universe. We will thus adopt the Friedman-Robertson-Walker flat metric for the Universe with the interval given by dsω are the redshift, comoving coordinate distance, cosmic time, and solid angle. Photons move along null geodesics, ds 2 = 0. The Friedman equations with the matter, dark energy (Λ), radiation/relativistic component and curvature density parameters Ω m , Ω Λ , Ω γ , Ω K lead to c(1 + z)dt/dz = R H /E(z), where E(z) ≡ [Ω γ (1 + z) 4 + Ω m (1 + z) 3 + Ω K (1 + z) 2 + Ω Λ f (z)] 1/2 with f (z) describing the evolution of DE and R H ≡ cH −1 0 . The Hubble constant is H(z) = H 0 E(z) and the distance measures become: the coordinate distance x(z) = c (1 + z)dt = R H z 0 dz/E(z), the comoving angular di-Advanced CCD Imaging Spectrometer -imaging arrays AEGIS XD All-wavelength Extended Groth strip International Survey -X-ray, deep AGB Asymptotic giant branch AKARI A Japane...

Spectral Properties of Populations Behind the Coherence in Spitzer Near-infrared and Chandra X-Ray Backgrounds

“…The source-subtracted CIB fluctuations could be contributed by the shot noise from remaining sources in the beam, and the clustering of the remaining CIB sources. The CIB fluctuations are measured at a given shot noise level, P SN = S 2 (m)dN(m), which we express in units of nJy nW m −2 sr −1 (see Kashlinsky et al 2018, Sect IV.A.1). The COSMOS maps are clipped to the shot noise level of ∼86 nJy nW m −2 sr −1 and other maps are at the level of ∼50 and ∼30 nJy nW m −2 sr −1 in 3.6 and 4.5 µm, respectively.…”

“…Following these theoretical proposals, Kashlinsky et al (2005Kashlinsky et al ( , 2007 identified in deep Spitzer-based analysis significant source-subtracted CIB fluctuations at levels much higher than expected from remaining known sources Helgason et al 2012Helgason et al , 2014. See the recent review by Kashlinsky et al (2018) for summary and discussion.…”

The clustering of undetected high-redshift black holes and their signatures in cosmic backgrounds

“…Using Spitzer data, Kashlinsky et al (2012) find marginal cross-correlations with the NIR and 8 micron emission, while Matsumoto et al (2011) find no cross-correlation with longer wavelength 100 micron maps with AKARI. In contrast, Thacker et al (2015) do report a cross-correlation at longer 250, 350, and 500 micron wavelengths, but Kashlinsky et al (2018) argues that the claimed signal may be derived from known Galactic populations. At the shorter wavelengths probed by HST, Mitchell-Wynne et al (2015) observe a clear power-law on scales > 1 , which they attribute to diffuse Galactic light.…”

“…Observationally, it has been difficult to estimate the contribution from Galactic cirrus to the NIR fluctuations, as discussed in detail in Kashlinsky et al (2018). The main method with which to assess its contribution has been to attempt to find cross-correlations with bands where cirrus is known to be dominant.…”

“…Fluctuation analyses of the measured CIB-its power spectrum or two-point correlation function-have revealed excess power on arcminute to degree scales on the sky that remain unexplained even with the most optimistic extrapolations of faint galaxy populations (Helgason et al 2012;Yue et al 2013a), pointing to an entirely new missing contribution to the inventory. This excess has now been seen in both the 3.6 and 4.5 micron bands by two different infrared telescopes (Kashlinsky 2005;Kashlinsky et al 2012;Matsumoto et al 2011), is detected in multiple independent fields, and has persisted through years of improved measurements (see Kashlinsky et al 2018, for a review).…”