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Published February 1, 2011 | Submitted + Published
Journal Article Open

A physical model for the origin of the diffuse cosmic infrared background and the opacity of the Universe to very high energy γ-rays

Abstract

We present a physical model for origin of the cosmic diffuse infrared background (CDIRB). By utilizing the observed stellar mass function and its evolution as input to a semi-empirical model of galaxy formation, we isolate the physics driving diffuse IR emission. The model includes contributions from three primary sources of IR emission: steady-state star formation owing to isolated disc galaxies, interaction-driven bursts of star formation owing to close encounters and mergers, and obscured active galactic nuclei (AGNs). We find that most of the CDIRB is produced by equal contributions from objects at z∼ 0.5–1 and z≳ 1, as suggested by recent observations. Of those sources, the vast majority of the emission originates in systems with low to moderate IR luminosities (L_(IR) ≲ 10¹² L_⊙); the most luminous objects contribute significant flux only at high redshifts (z ≳ 2). All star formation in ongoing mergers accounts for ≲10 per cent of the total at all wavelengths and redshifts, while emission directly attributable to the interaction-driven burst itself accounts for ≲5 per cent. We furthermore find that obscured AGNs contribute ≲1–2 per cent of the CDIRB at all wavelengths and redshifts, with a strong upper limit of less than 4 per cent of the total emission. Finally, since electron–positron pair production interactions with the CDIRB represent the primary source of opacity to very high energy (VHE: E_γ ≳ 1 TeV) γ-rays, the model provides predictions for the optical depth of the Universe to the most energetic photons. We find that these predictions agree with observations of high-energy cut-offs at ∼ TeV energies in nearby blazars, and suggest that while the Universe is extremely optically thick at ≳10 TeV, the next generation of VHE γ-ray telescopes can reasonably expect detections from out to ∼50–150 Mpc.

Additional Information

© 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS. Accepted 2010 August 24. Received 2010 July 5; in original form 2010 March 2. We thank the anonymous referee for helpful comments. Also thanks to Michael Kuhlen, Desika Narayanan and Chris Hayward for helpful conversations. JDY acknowledges support from NASA through Hubble Fellowship grant #HF-51266.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Support for PFH was provided by the Miller Institute for Basic Research in Science, University of California Berkeley. The computations in this paper were run on the Odyssey cluster supported by the FAS Research Computing Group at Harvard University

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Submitted - 1003.4733.pdf

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August 19, 2023
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