A low level of extragalactic background light as revealed by gamma-rays from blazars

Abstract

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the first stars, which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356-309 and 1ES 1101-232, at redshifts z=0.165 and z=0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources -- in particular from the first stars formed. This result also indicates that intergalactic space is more transparent to gamma-rays than previously thought.

15 pages, 7 figures. Accepted by Nature, in press (April 20 issue). Replaced with published version. Title changed, text and figures rearranged with addition of Supplementary Information

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• The possibility of multi-TeV secondary gamma rays from GRB221009A
• Prospects of additional contribution at Optical-NIR band of EBL in the light of VHE spectra
• The Contribution of Galaxies to the $3.4\mu \mathrm{m}$ Cosmic Infrared Background as Measured Using WISE
• Nonthermal Radiation of the Extreme TeV Blazar 1ES 0229+200 from Electromagnetic Cascades on Infrared Photon Field
• Redshift measurement of the BL-Lac gamma-ray blazar PKS 1424+240
• Very high energy $\gamma$-ray emission from RBS 0679
• Detecting a unique EBL signature with TeV gamma rays
• The First VHE Activity of OJ 287 and the Extragalactic Background Light
• Cascade Model of an Anomaly in Blazar Spectra at Very High Energy
• Rapid jet ejection from PKS 0215+015 coincident with a high-energy neutrino event
• H.E.S.S.: The High Energy Stereoscopic System
• Searches for very high energy gamma rays from blazars with CANGAROO-III telescope in 2005-2009
• Simultaneously unveiling the EBL and intrinsic spectral parameters of gamma-ray sources with Hamiltonian Monte Carlo
• The H.E.S.S. extragalactic sky
• Cosmic connections: from cosmic rays to gamma rays, to cosmic backgrounds and magnetic fields
• Detailed modelling of the EBL along VHE γ-ray paths
• Testing models of extragalactic $\gamma$-ray propagation using observations of extreme blazars in GeV and TeV energy ranges
• Extragalactic Background Light: Measurements and Applications
• Parsec-scale Structure and Kinematics of Faint TeV HBLs
• The H.E.S.S. Extragalactic Sky
• 130GeV gamma-ray line through axion conversion
• Predictions of TeV emission for a set of hard BL Lac objects
• Have Cherenkov telescopes detected a new light boson?
• A new light boson from MAGIC observations?
• Science Drivers for AGN Observations with the Cherenkov Telescope Array
• Physics Insights from Recent MAGIC AGN Observations
• NICER Perspective on TeV Blazar Mrk~421: X-ray Variability and Particle Acceleration