Fluctuation of the background sky in the Hubble Extremely Deep Field (XDF) and its origin

Abstract

We performed a fluctuation analysis of the Hubble Extremely Deep Field (XDF) at four optical wavelength bands and found large fluctuations that are significantly brighter than those expected for ordinary galaxies. Good cross-correlations with flat spectra are found down to 0.2 arcsec, indicating the existence of a spatial structure even at the 0.2 arcsec scale. The detected auto and cross-correlations provide a lower limit of 24 nW m −2 sr −1 for the absolute sky brightness at 700 ∼ 900 nm, which is consistent with previous observations. We searched for candidate objects to explain the detected large fluctuation using the catalog of the Hubble Ultra Deep Field (UDF), and found that the surface number density of faint compact objects (FCOs) rapidly increases toward the faint end. Radial profiles of FCOs are indistinguishable from the PSF, and the effective radius based on de Vaucouleur's law is estimated to be smaller than 0.02 arcsec. The SEDs of FCOs follow a power law at optical wavelengths, but show greater emission and structure at λ > 1µm. Assuming that the FCOs are the cause of the excess brightness and fluctuations, the faint magnitude limit is 34.9 mag for the F775W band, and the surface number density reaches 2.6 × 10 3 (arcsec) −2 .Recent γ ray observations require that the redshift of FCOs must be less than 0.1, if FCOs 1 are the origin of the excess optical and infrared background. Assuming that FCOs consist of missing baryons, the mass and luminosity of a single FCO range from 10 2 to 10 3 solar units, and mass-to-luminosity ratio is significantly lower than 1.0 solar unit. The maximum effective radius of an FCO is 4.7 pc. These results and the good correlation between near-infrared and X-ray background indicate that FCOs could be powered by the gravitational energy associated with black holes.

Probing Intra-Halo Light with Galaxy Stacking in CIBER Images

“…Additionally, EBL fluctuation analyses have also consistently reported excess fluctuations over those expected from the IGL (Kashlinsky et al 2005;Thompson et al 2007;Matsumoto et al 2011;Kashlinsky et al 2012;Cooray et al 2012;Zemcov et al 2014;Mitchell-Wynne et al 2015;Seo et al 2015;Kim et al 2019;Matsumoto & Tsumura 2019). One explanation is emission from the epoch of reionization (Kashlinsky et al 2005;Matsumoto et al 2011;Kashlinsky et al 2012;Mitchell-Wynne et al 2015), while other studies suggest IHL contributes most of the excess fluctuations (Cooray et al 2012).…”

On the origin of the optical and near-infrared extragalactic background light

“…To identify the origin of excess brightness and fluctuation, Matsumoto and Tsumura (2019) 83 ) (hereafter referred to as M&T) analyzed the fluctuation of XDF, which is the deepest image using HST. 84 ) They expected the appearance of new objects to be responsible for the excess brightness and fluctuation, since ILG arising from the ordinary galaxies is very low in XDF images after masking.…”

“…For a fluctuation analysis, M&T constructed a mask image by masking all plausible sources in a combined image (see details in Ref. 83 ), which was applied to the individual images. Eventually, 53.3% of the pixels remained.…”

“… 63 ) They also applied a simple correction for the masking effect, which is only slightly noticeable at large angles. 83 )…”

“…63) They also applied a simple correction for the masking effect, which is only slightly noticeable at large angles. 83) Figure 4 presents the fluctuations of four filter bands as a function of the angles, 2:/q. The shot noise at small angular scales and flat fluctuation patterns at angles larger than 10 arcsec are evident.…”