Recovering galaxy stellar population properties from broad-band spectral energy distribution fitting (1203.3548v2)

Abstract: (Abridged) We explore the dependence of galaxy stellar population properties derived from broad-band SED-fitting - such as age, stellar mass, dust reddening, etc. - on a variety of parameters, such as SFHs, metallicity, IMF, dust reddening and reddening law, and wavelength coverage. Mock galaxies serve as test particles. We confirm our earlier results based on real z=2 galaxies, that usually adopted \tau-models lead to overestimate the SFR and to underestimate the stellar mass. Here, we show that - for star-forming galaxies - ages, masses and reddening, can be well determined simultaneously only when the correct SFH is identified. This is the case for inverted-\tau-models at high-z, for which we find that the mass recovery (at fixed IMF) is as good as ~0.04 dex. Since the right SFH is usually unknown we quantify offsets generated by adopting standard fitting setups. Stellar masses are generally underestimated resulting from underestimating ages. For fitting setups with a variety of SFHs the median mass recovery at z ~ 2-3 is as decent as ~0.1 dex, albeit with large scatter. The situation worsens towards lower redshifts because of the variety of possible SFHs and ages (~0.6 dex at z=0.5). A practical trick to improve upon this is to exclude reddening from the fitting to avoid unrealistically young and dusty solutions. Reddening and SFRs should then be determined by a separate fit. As expected, the recovery of properties is better for passive galaxies. For the two galaxy types the parameter recovery is optimal for a wavelength coverage from the rest-frame UV to the rest-frame near-IR. We quantify the effect of narrowing the wavelength coverage or adding/removing filters which can be useful for planning observational surveys. Finally, we provide scaling relations that allow the transformation of stellar masses obtained using different template fitting setups and stellar population models.

Recovering Galaxy Properties from SED-Fitting: Insights and Implications

The paper by Pforr, Maraston, and Tonini presents a rigorous investigation into the retrieval of galaxy stellar population properties through broad-band spectral energy distribution (SED) fitting techniques. As this process underpins many conclusions in the field of galaxy formation and evolution, understanding the nuances of parameter choices and their implications is crucial.

Methodology and Findings

The authors employ a comprehensive approach, utilizing mock galaxies with known stellar properties to evaluate the effectiveness of various SED-fitting setups. These mock galaxies are categorized into star-forming and passive, spanning redshifts from 0.5 to 3. The paper uses both M05 and BC03 stellar population models to explore differences in derived properties like age, stellar mass, and star formation rates. The analysis further extends to the effects of diverse parameters, including star formation histories, metallicities, initial mass functions (IMFs), and wavelength coverage.

Key Conclusions:

• Star Formation Histories: The paper conclusively illustrates that the alignment between the chosen template and the actual star formation history is integral for accurate determination of galaxy properties. The paper highlights that standard $\tau$-models are prone to underestimating stellar masses and overestimating star formation rates, particularly in scenarios where massive stars overshadow older populations.
• Inverted-$\tau$ Models: The authors identify inverted-$\tau$ models as effective tools for fitting high-redshift star-forming galaxies, emphasizing how these models allow robust recovery of both stellar masses and star formation rates due to their alignment with the genuine growth patterns of such galaxies.
• Reddening and Wavelength Coverage: An efficient method to mitigate the biases induced by mismatched star formation histories is to exclude reddening from fitting parameters and to perform separate fits for star formation rates. Furthermore, optimal recovery of galaxy properties requires a spectral coverage encompassing the rest-frame UV to near-IR wavelengths.
• Metallicity and IMF Effects: Metallicity holds secondary importance relative to age determinations, while IMF exerts noticeable influence on the fitting results, particularly on stellar masses.
• Passive Galaxies: The research demonstrates that passive galaxy properties are generally easier to retrieve using SED-fitting due to their simpler star formation history and well-defined spectral features.

Implications and Further Research

The insights derived from this paper underscore the importance of selecting appropriate models and parameters tailored to specific galaxy types and epochs when conducting broad-band SED-fitting. This comprehensive evaluation serves as a guide for researchers aiming to maximize the accuracy of galaxy property determinations. As future telescopic surveys expand their scope and reach, these findings will be pivotal in optimizing observational strategies and improving the reliability of cosmological inferences drawn from galaxy data.

The paper also sets a foundation for further exploration into scaling relations that can homogenize results obtained across different template setups and models, enhancing the interoperability of data from various surveys. Such advancements will undoubtedly contribute to a more coherent and nuanced understanding of galaxy evolution, enabling new theoretical developments in astrophysics.