Diffuse Ultraviolet Sky Toward Nearby Galaxy Clusters

Abstract This study examines diffuse ultraviolet (UV) emissions in the PHOENIX_00 region near galaxy clusters using GALEX deep observations. In the far-UV (FUV) and near-UV (NUV), we detected backgrounds of 125–200 and 225–350 photon units (PU), with scatters of ±16 and ±22 PU, respectively. A moderate FUV-NUV correlation and FUV/NUV ratio below unity indicate FUV-dominated emission and little molecular hydrogen fluorescence or hot-line contributions. Dust influences the FUV background more strongly than the NUV, and UV band emissions correlate more strongly at Galactic latitudes <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>|</mml:mo> <mml:mi>gb</mml:mi> <mml:mo>|</mml:mo> <mml:mo>&gt;</mml:mo> <mml:mn>71</mml:mn> <mml:mover> <mml:mo>.</mml:mo> <mml:mtext>°</mml:mtext> </mml:mover> <mml:mn>29</mml:mn> </mml:math> . Infrared (IR) color ratios IR 60 /IR 100 (≈0.34 ± 0.03) indicate homogeneous large-grain temperatures and depletion of small grains and PAHs, while IR 60 /IR 25 below 3 indicates AGN activity in the region. The non-zero offsets of IR-UV plots 89 PU (FUV) and 199 PU (NUV) indicate the region’s baseline illumination and extragalactic radiation. Approximately 11% of the FUV offset and 23% of the NUV offset come from extragalactic background light, while the rest comes from dust-scattered starlight. Finally, our research shows that the interstellar radiation field directly affects the UV background, with the strength inversely proportional to local dust content.