[Paper Review] Measuring energy production in the Universe over all wavelengths and all time

Simon P. Driver|arXiv (Cornell University)|Feb 24, 2021

Astronomy and Astrophysical Research4 citations

TL;DR

This paper proposes a unified framework to measure the Cosmic Spectral Energy Distribution (CSED) by modeling energy production across all wavelengths and cosmic time, using integrated galaxy counts and dust reprocessing models. It achieves ~30% accuracy in predicting the extragalactic background light (EBL) from UV to far-IR, with future facilities enabling 1% precision and enabling falsifiable tests of star-formation and AGN evolution.

ABSTRACT

The study of the extragalactic background light (EBL) is undergoing a renaissance. New results from very high energy experiments and deep space missions have broken the deadlock between the contradictory measurements in the optical and near-IR arising from direct versus discrete source estimates. We are also seeing advances in our ability to model the EBL from gamma-ray to radio wavelengths with improved dust models and AGN handling. With the advent of deep and wide spectroscopic and photometric redshift surveys, we can now subdivide the EBL into redshift intervals. This allows for the recovery of the Cosmic Spectral Energy Distribution (CSED), or emissivity of a representative portion of the Universe, at any time. With new facilities coming online, and more unified studies underway from gamma-ray to radio wavelengths, it will soon be possible to measure the EBL to within 1 per cent accuracy. At this level correct modelling of reionisation, awareness of missing populations or light, radiation from the intra-cluster and halo gas, and any signal from decaying dark-matter all become important. In due course, the goal is to measure and explain the origin of all photons incident on the Earth's surface from the extragalactic domain, and within which is encoded the entire history of energy production in our Universe.

Motivation & Objective

• To resolve the long-standing discrepancy between direct and integrated galaxy count measurements of the Cosmic Optical and Infrared Background (COB/CIB).
• To model the full extragalactic background light (EBL) from γ-rays to radio waves using consistent physical assumptions.
• To reconstruct the Cosmic Spectral Energy Distribution (CSED) as a time-resolved measure of energy production across cosmic history.
• To enable falsifiable tests of star-formation history, dust models, and AGN contributions through comparison with future high-precision data.
• To lay the groundwork for measuring all extragalactic photon flux incident on Earth with 1% accuracy using upcoming multi-wavelength surveys.

Proposed method

• Uses integrated galaxy counts (IGL-EBL) and direct background measurements (direct-EBL) to constrain the EBL across UV to far-IR wavelengths.
• Applies a consistent physical model with Chabrier initial mass function (IMF), dust attenuation from Dale et al. (2019), and metallicity tracking the star-formation history.
• Models dust reprocessing of starlight, attributing ~50% of initial photons to re-emission in the far-IR, consistent with observational constraints.
• Constructs the Cosmic Spectral Energy Distribution (CSED) by subdividing the EBL into redshift bins, enabling time-resolved energy production tracking.
• Employs deep spectroscopic and photometric redshift surveys (e.g., DEVILS, WAVES, MOONS, PFS) to deconstruct the EBL into billion-year timeslices.
• Combines stacking of x-ray and radio data at galaxy locations to probe diffuse contributions in X-ray and radio domains.

Experimental results

Research questions

• RQ1 Can the discrepancy between direct and integrated galaxy count measurements of the COB/CIB be reconciled through a physically consistent model?
• RQ2 To what extent can the full EBL from UV to radio be modeled with current data and improved dust and AGN physics?
• RQ3 How accurately can the Cosmic Spectral Energy Distribution (CSED) be reconstructed to trace energy production at different cosmic epochs?
• RQ4 What role do missing populations, intra-cluster gas, or decaying dark matter play in shaping the EBL at sub-1% measurement accuracy?
• RQ5 Can future surveys (e.g., JWST, Euclid, LSST, eROSITA, CTA) achieve 1% precision in measuring the EBL from UV to mid-IR?

Key findings

• The model reproduces the observed COB and CIB to within ~30% accuracy across the optical to far-IR range, matching measurement uncertainties.
• The Cosmic Spectral Energy Distribution (CSED) at 7.5 billion years ago shows that energy production was dominated by unobscured and obscured AGN and disc components.
• The model successfully predicts the present-day EBL using only the cosmic star-formation history and basic assumptions on dust and IMF.
• Future surveys such as HST SkySURF, VST KiDS, VISTA VIKING, and DEVILS can achieve ~3% measurement accuracy of the EBL from UV to near-IR.
• The combination of deep spectroscopic surveys and improved radio and X-ray stacking techniques will enable CSED measurements into the X-ray and radio domains.
• With upcoming facilities like Messier, Euclid, Roman, and LSST, a 1% constraint on the UV to mid-IR EBL becomes feasible within the next decade.