[Paper Review] Updated analysis of near-infrared background fluctuations

Bin Yue, Andrea Ferrara+1 more|arXiv (Cornell University)|Jan 11, 2016

Particle Detector Development and Performance3 citations

TL;DR

This paper resolves a tension in interpreting near-infrared background (NIRB) fluctuations by showing that the correlation between CIBER 1.1/1.6 μm and Spitzer 3.6 μm bands is due to Diffuse Galactic Light (DGL), not early black holes. The DGL component explains large-scale fluctuations, allowing the Direct Collapse Black Hole (DCBH) scenario to remain viable and reducing required DCBH abundance by up to 30%.

ABSTRACT

The power spectrum of Near InfraRed Background (NIRB) fluctuations measured at 3.6 $μ$m by { t Spitzer} shows a clustering excess over the known galaxies signal that has been interpreted in terms of early ($z\simgt 13$), accreting (direct collapse) black holes (DCBH) or low-$z$ intrahalo light (IHL). In addition, these fluctuations correlate with the cosmic X-ray background (CXB) measured at (0.5-2) keV, supporting the black hole explanation. This scenario has been questioned by the recent detection of a correlation between the two { t CIBER} 1.1/1.6 $μ$m bands with the 3.6 $μ$m { t Spitzer} one. This correlation is hardly explained by early DCBHs that, due to intergalactic absorption, cannot contribute to the shortest wavelength bands. Here we show that the new correlation is caused instead by a Diffuse Galactic Light (DGL) component arising from Galactic stellar light scattered by dust. The black hole interpretation of the excess remains perfectly valid and, actually, the inclusion of DGL allows less demanding (by up to about 30\%) requirements on the DCBH abundance/mass.

Motivation & Objective

• To resolve the apparent contradiction between the observed cross-correlation of NIRB fluctuations at 1.1/1.6 μm (CIBER) and 3.6 μm (Spitzer) and the DCBH hypothesis.
• To assess whether the DGL component in the Milky Way can explain the observed cross-correlations at large angular scales.
• To evaluate whether the inclusion of DGL reduces the required abundance or mass of early DCBHs to explain the NIRB clustering excess.
• To test the consistency of the DCBH scenario with the observed cross-correlation between 3.6 μm NIRB and cosmic X-ray background (CXB) fluctuations.
• To determine whether the DCBH model can simultaneously fit the 3.6 μm auto-correlation and 3.6 μm–CXB cross-correlation power spectra.

Proposed method

• Model the 3.6 μm auto-correlation power spectrum as the sum of DGL, shot noise from low-redshift galaxies, and a clustering component from DCBHs.
• Use shot noise dominance at small scales (l ≳ 10^4) to isolate the shot noise component (C_SN) from CIBER data at 1.1 and 1.6 μm.
• Fit the DGL contribution to the 1.1 × 3.6 μm and 1.6 × 3.6 μm cross-correlation power spectra at large scales (l ≲ 300), assuming perfect correlation between bands.
• Model the DCBH contribution to the 3.6 μm auto-correlation and 3.6 μm–CXB cross-correlation using fiducial and reduced mass density models (ρ_• = 4×10^5 and 2.7×10^5 M⊙ Mpc⁻³).
• Compare the total predicted power spectra (DGL + low-z sources + DCBHs) with Spitzer and Cappelluti et al. (2013) CXB data.
• Assess the consistency of the DCBH model with the unresolved CXB intensity limit at 1.5 keV (Moretti et al., 2012).

Experimental results

Research questions

• RQ1 Can the observed cross-correlation between CIBER 1.1/1.6 μm and Spitzer 3.6 μm NIRB fluctuations be explained by a DGL component instead of early DCBHs?
• RQ2 To what extent does including DGL reduce the required DCBH mass density or abundance to explain the NIRB clustering excess?
• RQ3 Does the DCBH model remain consistent with the observed 3.6 μm–CXB cross-correlation power spectrum?
• RQ4 Is the predicted DCBH contribution to the CXB auto-correlation power spectrum consistent with observational limits?
• RQ5 Can the DGL component alone account for the large-scale fluctuations in the 3.6 μm power spectrum, with low-redshift galaxies contributing only at small scales?

Key findings

• The 1.1 × 3.6 μm and 1.6 × 3.6 μm cross-correlation power spectra at large scales (l ≲ 300) are well-fitted by a DGL component that dominates the 3.6 μm auto-correlation power spectrum on those scales.
• The DGL contribution to the 3.6 μm auto-correlation power spectrum is sufficient to explain the observed large-scale fluctuations, with low-redshift galaxies contributing primarily through shot noise at small scales.
• The inclusion of DGL reduces the required DCBH mass density by up to approximately 30%, making the DCBH scenario less demanding.
• The DCBH model, when combined with DGL and low-redshift sources, provides a good fit to the Spitzer 3.6 μm auto-correlation power spectrum across all scales.
• The DCBH contribution to the 3.6 μm–CXB cross-correlation power spectrum matches the observed data, while the predicted CXB auto-correlation from DCBHs remains below the unresolved CXB intensity limit.
• The model predicts a significant suppression of the NIRB–CXB correlation at wavelengths shorter than 3.6 μm, consistent with the absence of DCBH contributions due to intergalactic absorption.