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 and225-350 photon ...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 and225-350 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|gb|>71°.29.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 IR60/IR25 below 3 indicates AGN activity in the region.The non-zero offsets of IR-UV plots 89 PU(FUV)and199 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.展开更多
In this work,we present a systematic comp arison of single-and multiple-sc attering models for dust-scattered starlight across the UV sky and attempt to derive a simulation model of multiple-scattered radiation using ...In this work,we present a systematic comp arison of single-and multiple-sc attering models for dust-scattered starlight across the UV sky and attempt to derive a simulation model of multiple-scattered radiation using the single-scattered radiation.Our new simulated multiple-scattering model uses a critical angle(θ_(c)),which is dependent on optical depth(τ),albedo(a),and phase function asymmetry(g),to replace the computationally intensive full Monte Carlo treatment.We find that multiple-scattering becomes increasingly important in almost all optical depths,depending on the scattering geometry.UV-bright stars show a peak scattering intensity near the stellar disk,dropping by an order of magnitude within 10°-15°and merging with the background at 40°-50°,whereas fainter or more distant stars require larger angular separations to reach the same relative reduction.We introduce a functional form,I_(θ)=I_(0)(1-tanh(SP×θ)),to describe the radial decrease in scattered intensity,with the slope parameter declining systematically for more distant stars.Depending on a star's position,multiplescattered fluxes can exceed single-scattered fluxes by up to 200%,and both converge at a critical angle,θ_(c),which depends logarithmically on stellar distance and is governed byτ,a,and g.Notably,θ_(c)remains independent of Galactic longitude or latitude,underscoring the robust,geometry-driven nature of the scattering process.展开更多
The study of diffuse ultraviolet(UV)background radiation is vital in the investigation of stellar and galactic evolution.Space-based UV observations are comprised of both foreground and background radiations.The foreg...The study of diffuse ultraviolet(UV)background radiation is vital in the investigation of stellar and galactic evolution.Space-based UV observations are comprised of both foreground and background radiations.The foreground emission in an observation is a result of solar contamination in the direction of observation.In our previous work,we modeled airglow(one of the major constituents of the foreground emission)as a function of10.7 cm Solar Flux and Sun Angle with great accuracy using GALEX deep observations.We adopt a similar methodology to validate the obtained model and run equivalent experiments here using far-UV(FUV)and nearUV(NUV)GALEX medium imaging surveys(MIS)with a total exposure time greater than 3300 s.We obtained a predictive model having excellent compatibility with the earlier model.Our analysis shows that the total foreground emission varies between 59 and 295 photon units in FUV whereas in NUV,it varies between 671 and1195 photon units depending upon the date and time of observation.We also noticed a strong correlation between the background emission and optical depth both in FUV and NUV,especially in the low density regions.This clearly indicates that the major contributor in diffuse background radiation is the starlight scattered by interstellar dust grains.展开更多
文摘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 and225-350 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|gb|>71°.29.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 IR60/IR25 below 3 indicates AGN activity in the region.The non-zero offsets of IR-UV plots 89 PU(FUV)and199 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.
文摘In this work,we present a systematic comp arison of single-and multiple-sc attering models for dust-scattered starlight across the UV sky and attempt to derive a simulation model of multiple-scattered radiation using the single-scattered radiation.Our new simulated multiple-scattering model uses a critical angle(θ_(c)),which is dependent on optical depth(τ),albedo(a),and phase function asymmetry(g),to replace the computationally intensive full Monte Carlo treatment.We find that multiple-scattering becomes increasingly important in almost all optical depths,depending on the scattering geometry.UV-bright stars show a peak scattering intensity near the stellar disk,dropping by an order of magnitude within 10°-15°and merging with the background at 40°-50°,whereas fainter or more distant stars require larger angular separations to reach the same relative reduction.We introduce a functional form,I_(θ)=I_(0)(1-tanh(SP×θ)),to describe the radial decrease in scattered intensity,with the slope parameter declining systematically for more distant stars.Depending on a star's position,multiplescattered fluxes can exceed single-scattered fluxes by up to 200%,and both converge at a critical angle,θ_(c),which depends logarithmically on stellar distance and is governed byτ,a,and g.Notably,θ_(c)remains independent of Galactic longitude or latitude,underscoring the robust,geometry-driven nature of the scattering process.
基金NASA's GALEX programSTScI is operated by the Association of Universities for Research in Astronomy,Inc.,under NASA contract NAS5-26555+1 种基金Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contractsthe support of DST-FIST。
文摘The study of diffuse ultraviolet(UV)background radiation is vital in the investigation of stellar and galactic evolution.Space-based UV observations are comprised of both foreground and background radiations.The foreground emission in an observation is a result of solar contamination in the direction of observation.In our previous work,we modeled airglow(one of the major constituents of the foreground emission)as a function of10.7 cm Solar Flux and Sun Angle with great accuracy using GALEX deep observations.We adopt a similar methodology to validate the obtained model and run equivalent experiments here using far-UV(FUV)and nearUV(NUV)GALEX medium imaging surveys(MIS)with a total exposure time greater than 3300 s.We obtained a predictive model having excellent compatibility with the earlier model.Our analysis shows that the total foreground emission varies between 59 and 295 photon units in FUV whereas in NUV,it varies between 671 and1195 photon units depending upon the date and time of observation.We also noticed a strong correlation between the background emission and optical depth both in FUV and NUV,especially in the low density regions.This clearly indicates that the major contributor in diffuse background radiation is the starlight scattered by interstellar dust grains.
