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Large and small-scale structures and the dust energy balance problem in spiral galaxies

Waad Saftly (UGent) , Maarten Baes (UGent) , Gert De Geyter, Peter Camps (UGent) , F Renaud, J Guedes and Ilse De Looze (UGent)
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Abstract
The interstellar dust content in galaxies can be traced in extinction at optical wavelengths, or in emission in the far-infrared. Several studies have found that radiative transfer models that successfully explain the optical extinction in edge-on spiral galaxies generally underestimate the observed FIR/submm fluxes by a factor of about three. In order to investigate this so-called dust energy balance problem, we use two Milky Way-like galaxies produced by high-resolution hydrodynamical simulations. We create mock optical edge-on views of these simulated galaxies (using the radiative transfer code SKIRT), and we then fit the parameters of a basic spiral galaxy model to these images (using the fitting code FitSKIRT). The basic model includes smooth axisymmetric distributions along a Sersic bulge and exponential disc for the stars, and a second exponential disc for the dust. We find that the dust mass recovered by the fitted models is about three times smaller than the known dust mass of the hydrodynamical input models. This factor is in agreement with previous energy balance studies of real edge-on spiral galaxies. On the other hand, fitting the same basic model to less complex input models (e.g. a smooth exponential disc with a spiral perturbation or with random clumps), does recover the dust mass of the input model almost perfectly. Thus it seems that the complex asymmetries and the inhomogeneous structure of real and hydrodynamically simulated galaxies are a lot more efficient at hiding dust than the rather contrived geometries in typical quasi-analytical models. This effect may help explain the discrepancy between the dust emission predicted by radiative transfer models and the observed emission in energy balance studies for edge-on spiral galaxies.
Keywords
MOLECULAR CLOUDS, STELLAR RADIATION, NEARBY GALAXIES, galaxies: ISM, hydrodynamics, methods: numerical, RADIATIVE-TRANSFER SIMULATIONS, EDGE-ON GALAXIES, DISC GALAXIES, INTERSTELLAR-MEDIUM, HIGH-RESOLUTION, HERSCHEL-ATLAS, MULTIPLE-SCATTERING, radiative transfer

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Citation

Please use this url to cite or link to this publication:

MLA
Saftly, Waad et al. “Large and Small-scale Structures and the Dust Energy Balance Problem in Spiral Galaxies.” ASTRONOMY & ASTROPHYSICS 576 (2015): n. pag. Print.
APA
Saftly, W., Baes, M., De Geyter, G., Camps, P., Renaud, F., Guedes, J., & De Looze, I. (2015). Large and small-scale structures and the dust energy balance problem in spiral galaxies. ASTRONOMY & ASTROPHYSICS, 576.
Chicago author-date
Saftly, Waad, Maarten Baes, Gert De Geyter, Peter Camps, F Renaud, J Guedes, and Ilse De Looze. 2015. “Large and Small-scale Structures and the Dust Energy Balance Problem in Spiral Galaxies.” Astronomy & Astrophysics 576.
Chicago author-date (all authors)
Saftly, Waad, Maarten Baes, Gert De Geyter, Peter Camps, F Renaud, J Guedes, and Ilse De Looze. 2015. “Large and Small-scale Structures and the Dust Energy Balance Problem in Spiral Galaxies.” Astronomy & Astrophysics 576.
Vancouver
1.
Saftly W, Baes M, De Geyter G, Camps P, Renaud F, Guedes J, et al. Large and small-scale structures and the dust energy balance problem in spiral galaxies. ASTRONOMY & ASTROPHYSICS. 2015;576.
IEEE
[1]
W. Saftly et al., “Large and small-scale structures and the dust energy balance problem in spiral galaxies,” ASTRONOMY & ASTROPHYSICS, vol. 576, 2015.
@article{7058683,
  abstract     = {The interstellar dust content in galaxies can be traced in extinction at optical wavelengths, or in emission in the far-infrared. Several studies have found that radiative transfer models that successfully explain the optical extinction in edge-on spiral galaxies generally underestimate the observed FIR/submm fluxes by a factor of about three. In order to investigate this so-called dust energy balance problem, we use two Milky Way-like galaxies produced by high-resolution hydrodynamical simulations. We create mock optical edge-on views of these simulated galaxies (using the radiative transfer code SKIRT), and we then fit the parameters of a basic spiral galaxy model to these images (using the fitting code FitSKIRT). The basic model includes smooth axisymmetric distributions along a Sersic bulge and exponential disc for the stars, and a second exponential disc for the dust. We find that the dust mass recovered by the fitted models is about three times smaller than the known dust mass of the hydrodynamical input models. This factor is in agreement with previous energy balance studies of real edge-on spiral galaxies. On the other hand, fitting the same basic model to less complex input models (e.g. a smooth exponential disc with a spiral perturbation or with random clumps), does recover the dust mass of the input model almost perfectly. Thus it seems that the complex asymmetries and the inhomogeneous structure of real and hydrodynamically simulated galaxies are a lot more efficient at hiding dust than the rather contrived geometries in typical quasi-analytical models. This effect may help explain the discrepancy between the dust emission predicted by radiative transfer models and the observed emission in energy balance studies for edge-on spiral galaxies.},
  articleno    = {A31},
  author       = {Saftly, Waad and Baes, Maarten and De Geyter, Gert and Camps, Peter and Renaud, F and Guedes, J and De Looze, Ilse},
  issn         = {0004-6361},
  journal      = {ASTRONOMY & ASTROPHYSICS},
  keywords     = {MOLECULAR CLOUDS,STELLAR RADIATION,NEARBY GALAXIES,galaxies: ISM,hydrodynamics,methods: numerical,RADIATIVE-TRANSFER SIMULATIONS,EDGE-ON GALAXIES,DISC GALAXIES,INTERSTELLAR-MEDIUM,HIGH-RESOLUTION,HERSCHEL-ATLAS,MULTIPLE-SCATTERING,radiative transfer},
  language     = {eng},
  pages        = {9},
  title        = {Large and small-scale structures and the dust energy balance problem in spiral galaxies},
  url          = {http://dx.doi.org/10.1051/0004-6361/201425445},
  volume       = {576},
  year         = {2015},
}

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