The Diffuse Radiation Field at High Galactic Latitudes

Akshaya, M S; Murthy, Jayant; Ravichandran, Sathish Kumar; Henry, R. C.; Overduin, James

doi:10.3847/1538-4357/aabcb9

Cited by 30 publications

(58 citation statements)

References 61 publications

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“…We have studied the latitude range between 70 • and 80 • as a continuation of our characterisation of the diffuse UV sky. This region has a greater amount of nebulosity and hence higher column densities than our earlier study at the Galactic Poles (Akshaya et al 2018). We confirm the presence of an offset at zero column density (E(B -V) = 0) with a level of 240 ± 18 photon units in the FUV and 394 ± 37 photon units in the NUV, slightly higher than in the polar regions (Akshaya et al 2018).…”

Section: Discussionsupporting

confidence: 73%

Components of the diffuse ultraviolet radiation at high latitudes

Akshaya

Murthy

Ravichandran

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We have used data from the Galaxy Evolution Explorer to study the different components of the diffuse ultraviolet background in the region between the Galactic latitudes 70 • -80 • . We find an offset at zero dust column density (E(B -V) = 0) of 240 ± 18 photon units in the FUV (1539Å) and 394 ± 37 photon units in the NUV (2316 A). This is approximately half of the total observed radiation with the remainder divided between an extragalactic component of 114 ± 18 photon units in the FUV and 194 ± 37 photon units in the NUV and starlight scattered by Galactic dust at high latitudes. The optical constants of the dust grains were found to be a=0.4±0.1 and g=0.8±0.1 (FUV) and a=0.4±0.1 and g=0.5±0.1 (NUV). We cannot differentiate between a Galactic or extragalactic origin for the zero-offset but can affirm that it is not from any known source.

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Section: Discussionsupporting

confidence: 73%

Components of the diffuse ultraviolet radiation at high latitudes

Akshaya

Murthy

Ravichandran

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Their final diffuse radiation maps in FUV and NUV are dominated by starlight scattered by Milky Way dust, especially at low latitudes. At high latitudes, the extragalactic contribution is significant but its amplitude is under debate, due to the uncertainties in the near-Earth and Galactic foregrounds (Hamden et al 2013;Henry et al 2015;Akshaya et al 2018). Our cross-correlation analysis has the advantage that the result should not be biased by the presence of foregrounds, as they only add noise but do not correlate with extragalactic large-scale structures.…”

Section: Diffuse Lightmentioning

confidence: 99%

Broadband Intensity Tomography: Spectral Tagging of the Cosmic UV Background

Chiang

Ménard

Schiminovich

2019

ApJ

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Cosmic photons can be efficiently collected by broadband intensity mapping but information on their emission redshift and frequency is largely lost. We introduce a technique to statistically recover these otherwise collapsed dimensions by exploiting information in spatial fluctuations and apply it to the Galaxy Evolution Explorer (GALEX) All Sky and Medium Imaging Surveys. By spatially cross-correlating photons in the GALEX far-UV (1500 Å) and near-UV (2300 Å) bands with a million spectroscopic objects in the Sloan Digital Sky Survey as a function of redshift, we robustly detect the redshift-dependent intensity of the UV background (UVB) modulated by its clustering bias up to z ∼ 2. These measurements clearly reveal the imprints of UVB spectral features redshifting through the filters. Using a simple parameterization, we simultaneously fit a UVB emissivity and clustering bias factor to these observations and constrain the main spectral features of the UVB spectrum: (i) the Lyman break, (ii) the non-ionizing UV continuum, which agrees with the Haardt & Madau model but does not rely on any assumption regarding the nature of the sources, and (iii) the Lyα emission, whose luminosity density is consistent with estimates of the combined galaxy and AGN contributions at z ∼ 1. Because the technique probes the total background including low surface brightness emission, we place constraints on the amount of UV light originating from the diffuse intergalactic medium (IGM). Finally, the clustering bias of UV photons is found to be chromatic and evolving. Our frequency-and redshift-dependent UVB measurement delivers a summary statistic of the universe's net radiation output from stars, black holes, and the IGM combined.

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“…The all-sky nature of the GALEX and the SPEAR observations have allowed us to separate the components based on their distribution over the sky. The foreground emission (airglow and zodiacal light) is dependent on the observation time and date and Murthy (2014b) has characterized their contribution to the total diffuse background in the GALEX data while Akshaya et al (2018Akshaya et al ( , 2019 have mapped the contributions from the Galactic and extragalactic components at high latitudes. Similarly, Seon et al (2011) andJo et al (2017) have mapped the diffuse emission observed by SPEAR, both the continuum dust emission and the molecular hydrogen fluorescence with the advantage over GALEX of spectroscopy but a poorer sensitivity and spatial resolution.…”

Section: Introductionmentioning

confidence: 99%

“…Of all the contributors to the diffuse observations, the only one which might be expected to be time-variable is the airglow, which is a function of the local time of observation (Murthy 2014b), and it was a surprise when Akshaya et al (2018) found time-variable variations in the GALEX observations in Virgo, which they attributed to unknown atmospheric sources. GALEX was never intended to probe variability in the DGL and it is difficult now, after the mission has ended, to divine the source of the variability.…”

Section: Introductionmentioning

confidence: 99%

Time variations in the UV background

Murthy¹,

Gowtham²

2022

Preprint

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We have found variations in the diffuse ultraviolet background on the scale about 10 days over the 10 year life of the GALEX mission. These variations are only apparent in the near-ultraviolet band of GALEX and are most likely related to variations in the zodiacal light due to brightness variations of the solar NUV flux. The variations can be as high as 200 photon units in the NUV, amounting to about 15% of the zodiacal light or < 10% of the total NUV diffuse radiation. There is no effect on the far-ultraviolet band of GALEX. Further work will require better observations chosen specifically for the purpose of investigating this component and will be difficult to obtain.

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The Diffuse Radiation Field at High Galactic Latitudes

Cited by 30 publications

References 61 publications

Components of the diffuse ultraviolet radiation at high latitudes

Components of the diffuse ultraviolet radiation at high latitudes

Broadband Intensity Tomography: Spectral Tagging of the Cosmic UV Background

Time variations in the UV background

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