A measurement of the z = 0 UV background from H$\alpha$ fluorescence

Abstract

We report the detection of extended Halpha emission from the tip of the HI disk of the nearby edge-on galaxy UGC 7321, observed with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope. The Halpha surface brightness fades rapidly where the HI column density drops below N(HI) = 10^19 cm^-2 , consistent with fluorescence arising at the ionisation front from gas that is photoionized by the extragalactic ultraviolet background (UVB). The surface brightness measured at this location is (1.2 +/- 0.5)x10^-19 erg/s/cm^2/arcsec^2, where the error is mostly systematic and results from the proximity of the signal to the edge of the MUSE field of view, and from the presence of a sky line next to the redshifted Halpha wavelength. By combining the Halpha and the HI 21 cm maps with a radiative transfer calculation of an exponential disk illuminated by the UVB, we derive a value for the HI photoionization rate of Gamma ~ (6-8)x10^-14 1/s . This value is consistent with transmission statistics of the Lyalpha forest and with recent models of a UVB which is dominated by quasars.

15 pages, 11 figures. Published in MNRAS

References in corpus (12)

• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• Massloss of galaxies due to a UV-background
• The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization
• Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity
• A Population of Faint Extended Line Emitters and the Host Galaxies of Optically Thick QSO Absorption Systems
• The Photon Underproduction Crisis
• MUSE searches for galaxies near very metal-poor gas clouds at z~3: new constraints for cold accretion models
• The properties of "dark" ΛCDM halos in the Local Group
• VoIgt profile Parameter Estimation Routine (VIPER): H I photoionization rate at z<0.5
• The Line-of-Sight Proximity Effect and the Mass of Quasar Host Halos
• Detection of [OI] 6300 and Other Diagnostic Emission Lines in the Diffuse Ionized Gas of M33 with Gemini-North
• The existence and detection of optically dark galaxies by 21cm surveys

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