MCMC determination of the cosmic UV background at z similar or equal to 0 from H alpha fluorescence
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Date
2019-01
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Journal Article
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yes
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Abstract
In a recent paper we reported on the detection of a diffuse Hα glow in the outskirts of the nearby, edge-on disc galaxy UGC 7321 observed with the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope. By interpreting the H α emission as fluorescence arising from hydrogen ionized by an external (i.e. extragalactic) radiation field, we estimated the UV background (UVB) intensity in terms of H I ionization rate (per ion) at z ≃ 0 to be in the range ΓHI ∼ 6 − 8 × 10⁻¹⁴ s⁻¹. In the present work, by performing radiative transfer calculations over a large set of models of the gaseous disc of UGC 7321, we refine our estimate and through an MCMC analysis derive a value for the photoionization rate of ΓHi=7.27⁺².⁹³₋₂.₉₀×10⁻¹⁴ s⁻¹. In particular, our analysis demonstrates that this value is robust against large variations in the galaxy model and that the uncertainties are mainly driven by the errors associated with the observed H α surface brightness. Our measurement is consistent with several recent determinations of the same quantity by a completely independent technique (i.e. flux decrement analysis of the Lyα forest), and support the notion that the low-redshift UVB is largely dominated by active galactic nuclei, possibly with no need of further contribution from star-forming galaxies.
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published
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Journal / series
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482 (2)
Pages / Article No.
2833 - 2837
Publisher
Oxford University Press
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Subject
radiative transfer; methods: numerical; intergalactic medium; cosmology: theory
Organisational unit
09592 - Cantalupo, Sebastiano (ehemalig) / Cantalupo, Sebastiano (former)
Notes
It was possible to publish this article open access thanks to a Swiss National Licence with the publisher.
Funding
163824 - From Cosmic Web to Galaxies: Illuminating the Gaseous Link between the Dark and the Bright Universe (SNF)