Ultraviolet Radiative Transfer Modeling of Nearby Galaxies with Extraplanar Dusts

Abstract

In order to examine their relation to the host galaxy, the extraplanar dust of six nearby galaxies are modeled, employing a three dimensional Monte Carlo radiative transfer code. The targets are from the highly-inclined galaxies that show dust-scattered ultraviolet halos, and the archival Galaxy Evolution Explorer FUV band images were fitted with the model. The observed images are in general well reproduced by two dust layers and one light-source layer, whose vertical and radial distributions have exponential profiles. We obtained several important physical parameters, such as star formation rate (SFR_UV), face-on optical depth, and scale-heights. Three galaxies (NGC 891, NGC 3628, and UGC 11794) show clear evidence for the existence of extraplanar dust layer. However, it is found that the rest three targets (IC 5249, NGC 24, and NGC 4173) do not necessarily need a thick dust disk to model the ultraviolet (UV) halo, because its contribution is too small and the UV halo may be caused by the wing part of the GALEX point spread function. This indicates that the galaxy samples reported to have UV halos may be contaminated by galaxies with negligible extraplanar (halo) dust. The galaxies showing evidence of the extraplanar dust layer fall within a narrow range on the scatter plots between physical parameters such as SFR_UV and extraplanar dust mass. Several mechanisms possible to produce the extraplanar dust are discussed. We also found a hint that the extraplanar dust scale-height might not be much different from the polycyclic aromatic hydrocarbon emission characteristic height.

33 pages, 7 figures, 5 tables, ApJ in press

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• The Halos and Environments of Nearby Galaxies (HERON) II: The outer structure of edge-on galaxies
• Comparison of the extraplanar H$\alpha$ and UV emissions in the halos of nearby edge-on spiral galaxies
• The distribution of dust in edge-on galaxies: I. The global structure
• The nature of the UV halo around the spiral galaxy NGC 3628
• Candidate List of Edge-on Galaxies with Substantial Extraplanar Dust
• Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS) II. Revisiting the ionisation mechanism of the extraplanar diffuse ionised gas
• Polarization as a probe of thick dust disk in edge-on galaxies: application to NGC 891
• Constraining the top-light initial mass function in the extended ultraviolet disk of M83
• Observing the Earliest Stages of Star Formation in Galaxies: 8 micron Cores in Three Edge-on Disks
• Radiative transfer in disc galaxies $-$ V. The accuracy of the KB approximation
• Seeking Edge-on Galaxies with Substantial Extraplanar Dust Using a Radiative Transfer Model: Determination of the Model Parameter Uncertainties for EON_10.477_41.954 (FGC 79)
• Extraplanar emission in isolated edge-on late-type galaxies. I. The H$\alpha$ distribution versus to the old and young stellar discs
• Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- IV: Program overview and first results on the polarization fraction
• The core starbursts of the galaxy NGC 3628: Radio very long baseline interferometry and X-ray studies