The cosmic radio background from 150 MHz to 8.4 GHz and its division into AGN and star-forming galaxy flux

Abstract

We present a revised measurement of the extra-galactic background light (EBL) at radio frequencies based on a near complete compendium of radio source counts. We present the radio-EBL at 150 MHz, 325 MHz, 610 MHz, 1.4 GHz, 3 GHz, 5 GHz, and 8.4 GHz. In all cases the contribution to the radio-EBL, per decade of flux, exhibits a two-humped distribution well matched to the AGN and star-forming galaxy (SFG) populations, and with each population contributing roughly equal energy. Only at 3 GHz are the source count contributions to the EBL fully convergent, and hence we report empirical lower limits to the radio-EBL in the remaining bands. Adopting predictions from the SHARK semi-analytic model for the form of the SFG population, we can fit the fainter source counts providing measurements of the total contribution to the radio-EBL for the SFG and the AGN populations separately. This constitutes an empirically constrained model-dependent measurement for the SFG contribution, but a fully empirical measurement of the AGN contribution. Using the ProSpect spectral energy distribution code we can model the UV-optical-infrared-mm-radio SFG EBL at all frequencies from the cosmic star-formation history and the adoption of a Chabrier initial mass function. However, significant discrepancy remains (5 ×) between our source-count estimates of the radio-EBL and the direct measurements reported from the ARCADE-2 experiment. We can rule out a significant missing discrete source radio population and suggest that the cause of the high ARCADE-2 radio-EBL values may need to be sought either in the foreground subtraction or as a yet unknown diffuse component in the radio sky.

The impact of a modified CMB photon density on UHECR propagation

“…Among its characteristics, there is an intriguing anomaly observed in the CMB line temperature at low frequencies, starting at around 1 GHz [9,10,21]. While radio sources originating from within our galaxy offer a plausible explanation, they fail to account for the isotropic nature of the excess radiation [21,23]. Another potential contributor to this foreground signal could be the decay of axions with a mass of approximately 30 𝜇eV (8 GHz); compare [8] for a general discussion of axion decays at radio frequencies.…”

Structure Formation Paradigm and Axion Quark Nugget dark matter model

“…with dark photon DM model [50]. Another recent example is the observed excess in radio frequency bands, ν ∈ (150 MHz, 8.4 GHz) where significant discrepancy remains as large as factor ∼ 5 [51].…”

JWST NIRCam Photometry: A Study of Globular Clusters Surrounding Bright Elliptical Galaxy VV 191a at z = 0.0513

“…Table 1 and Figure 3 show our procedure to estimate the number of background galaxies behind VV 191a and how these may affect the GC sample in each of the ringlets in Figure 2. Table 1 shows each of the adopted elliptical ringlet areas in arcsec 2 , the number of detected GC candidates, and the number of background galaxies from m AB = 24 mag down to the detection limits (AB  27.2-28 mag) expected in each ringlet area, following Figures 6-8 and Section 4 of Windhorst et al (2023) and the integration method of Tompkins et al (2023), with a cosmic variance on the integrated galaxy counts of 10% (see Section 4 and Appendix B2 of Windhorst et al 2023). This amounts to 496,300 galaxies deg −2 (or 0.0383 arcsec −2 ) over the magnitude range 24 mag  m AB  27.2 mag in F090W.…”