The distribution of interstellar dust in CALIFA edge-on galaxies via oligochromatic radiative transfer fitting (1403.7527v1)

Abstract: We investigate the amount and spatial distribution of interstellar dust in edge-on spiral galaxies, using detailed radiative transfer modeling of a homogeneous sample of 12 galaxies selected from the CALIFA survey. Our automated fitting routine, FitSKIRT, was first validated against artificial data. This is done by simultaneously reproducing the SDSS $g$-, $r$-, $i$- and $z$-band observations of a toy model in order to combine the information present in the different bands. We show that this combined, oligochromatic fitting, has clear advantages over standard monochromatic fitting especially regarding constraints on the dust properties. We model all galaxies in our sample using a three-component model, consisting of a double exponential disc to describe the stellar and dust discs and using a S\'ersic profile to describe the central bulge. The full model contains 19 free parameters, and we are able to constrain all these parameters to a satisfactory level of accuracy without human intervention or strong boundary conditions. Apart from two galaxies, the entire sample can be accurately reproduced by our model. We find that the dust disc is about 75% more extended but only half as high as the stellar disc. The average face-on optical depth in the V-band is $0.76$ and the spread of $0.60$ within our sample is quite substantial, which indicates that some spiral galaxies are relatively opaque even when seen face-on.

Insights into the Interstellar Dust Distribution in CALIFA Edge-On Spiral Galaxies

The paper detailed in the paper, "The distribution of interstellar dust in CALIFA edge-on galaxies via oligochromatic radiative transfer fitting", presents a comprehensive analysis of interstellar dust distribution within a sample of 12 edge-on spiral galaxies chosen from the CALIFA survey. The authors leverage a robust radiative transfer modeling approach to derive insights into the spatial distribution and characteristics of dust within these galaxies, focusing on oligochromatic fitting techniques which improve the precision of parameter estimation over traditional monochromatic methods. This approach provides a nuanced understanding of dust properties by simultaneously integrating data from multiple observational bands.

Methodology and Validation

The core methodology centers on the application of FitSKIRT, an automated fitting routine which integrates the SKIRT radiative transfer code. This combination employs advanced genetic algorithm techniques to optimize model fits to multi-band imaging data, specifically the SDSS $g$-, $r$-, $i$-, and $z$-bands. The oligochromatic fitting process, which simultaneously processes images from multiple wavelengths, allows for a more precise constraint of dust parameters, thereby addressing parameter degeneracies that are often present in monochromatic fitting scenarios.

FitSKIRT's efficacy is first established through validation against synthetic data, demonstrating its capability to recover known input parameters with satisfactory accuracy. The paper underscores that the oligochromatic approach not only enhances accuracy but also provides robust solutions by balancing information extracted from different wavelength regimes.

Key Findings

The analysis reveals several salient features regarding the dust distribution in the studied galaxies. Typically, the dust disc is found to be more radially extended and thinner compared to the stellar disc, corroborating previous findings while offering refined quantitative insights. The mean dust-to-stellar scale height ratio is approximately 0.50, indicating that dust discs are about half as thick as the stellar discs.

The paper also measures the face-on optical depth in the V-band with a mean of 0.76 and a substantial spread of 0.60 within the sample. This variability suggests a broad range of opacities among spiral galaxies, with potential implications for the interpretation of light attenuation and star visibility in extragalactic studies.

An intriguing observation is the tentative relation between dust-to-stellar scale height ratios and the bulge-to-disc ratio. This suggests a potential structural influence on dust distribution, although the underlying mechanisms remain speculative and warrant further investigation.

Implications and Future Directions

The implications of this research extend into both practical and theoretical domains. From a practical perspective, the improved characterization of dust properties has consequences for understanding the obscuration and energy budgets of galaxies. The enhanced accuracy of oligochromatic fitting implies these methods could be crucial in similar studies, suggesting a paradigm shift from traditional single-band analyses.

Theoretically, the variability in dust characteristics like the face-on optical depth speaks to the diverse evolutionary histories and structural properties of spiral galaxies. Furthermore, the observed correlation between structural parameters and dust distribution invites future research into the potential feedback mechanisms between star formation, galactic morphology, and dust evolution.

Looking ahead, integrating these radiative transfer results with multi-wavelength data extending into the FIR could provide deeper insight into the dust energy balance, a longstanding issue in galaxy evolution studies. The authors suggest future work could include the calculation of expected FIR/submm emissions from the derived models, compared against actual observed data, to quantifiably address the dust energy discrepancy.

Ultimately, this research not only advances our understanding of dust characteristics in edge-on spiral galaxies but also refines methodological approaches for future explorations in extragalactic astrophysics.