Recovering galaxy stellar population properties from broad-band spectral energy distribution fitting – II. The case with unknown redshift
Recovering galaxy stellar population properties from broad-band spectral energy distribution fitting – II. The case with unknown redshift
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从宽带光谱能量分布拟合中恢复星系恒星种群特性——红移未知的情况
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发表时间：
2013
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通讯作者：
Australia.
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作者：
J. Pforr;C. Maraston;C. K. N. O. A. Observatory;Tucson;Usa Institute of Cosmology;Gravitation;U. Portsmouth;UK Harvard;Supercomputing;S. U. Technology;Australia.
在最近的一项工作（论文 I）中，我们探讨了宽带光谱能量分布拟合得出的星系恒星种群特性对拟合参数的依赖性，例如恒星形成历史 (SFH)、年龄网格、金属丰度、初始质量函数 (IMF)、尘埃红化和红化定律、滤波器设置和波长覆盖范围。在本文中，我们考虑红移也是拟合中的自由参数的情况，并研究是否可以立即获得光度红移和恒星种群属性的合理估计。与论文 I 一样，我们使用模拟恒星形成以及处于不同红移 (0.5-3) 的被动星系作为测试粒子。模拟恒星形成星系是从半解析星系形成模型中提取的。我们表明，对于高红移恒星形成星系，当使用宽波长覆盖范围（包括莱曼和 4000 A 断裂）和拟合中的宽模板设置时，可以同时确定光度红移、恒星质量和红化。与固定红移时一样，质量也得到了类似的良好恢复（中位〜0.2 dex）。对于近期恒星形成很少的老星系（在模拟中处于较低的红移），质量比固定红移情况更好地恢复，使得恢复的恒星质量中位数提高了高达 0.3 dex（在固定 IMF 下），而红移精度的不确定性仅增加~0.05。然而，红移恢复的失败也意味着质量恢复的失败。与固定红移一样，SFH 的不匹配以及年龄、尘埃和现在的红移之间的简并导致了年龄的低估、红化的高估和质量的低估。恒星质量最好在低红移时确定，而不会在拟合中变红。然后质量仅被低估~0.1 dex，而红移同样得到很好的恢复。毫不奇怪，对于被动星系来说，属性的恢复要好得多，例如对于被动星系来说。使用包括金属丰度效应的设置，质量的恢复仅比固定红移时稍差（在固定 IMF 下被低估约 0.02 dex，而不是约 0.01）。在所有情况下，物理参数的恢复关键取决于拟合中采用的波长覆盖范围，因为红移恢复取决于波长覆盖范围。众所周知，红移最好在包括莱曼和 4000 A 断裂的波长范围内恢复。与论文 I 一样，对改变模板、波长覆盖范围和滤波器的所有影响进行了量化，并提供了使用不同拟合参数（包括恒星种群模型）获得的恒星质量转换的缩放关系。
In a recent work (Paper I), we explored the dependence of galaxy stellar population properties derived from broad-band spectral energy distribution fitting on the fitting parameters, e.g. star formation histories (SFHs), age grid, metallicity, initial mass function (IMF), dust reddening and reddening law, filter setup and wavelength coverage. In this paper, we consider the case that also redshift is a free parameter in the fit and study whether one can obtain reasonable estimates of photometric redshifts and stellar population properties at once. As in Paper I, we use mock star-forming as well as passive galaxies placed at various redshifts (0.5–3) as test particles. Mock star-forming galaxies are extracted from a semi-analytical galaxy formation model. We show that for high-redshift star-forming galaxies, photometric redshifts, stellar masses and reddening can be determined simultaneously when using a broad wavelength coverage (including the Lyman and the 4000 A break) and a wide template setup in the fit. Masses are similarly well recovered (median ∼0.2 dex) as at fixed redshift. For old galaxies with little recent star formation (which are at lower redshift in the simulation), masses are better recovered than in the fixed redshift case, such that the median recovered stellar mass improves by up to 0.3 dex (at fixed IMF) whereas the uncertainty in the redshift accuracy increases by only ∼0.05. However, a failure in redshift recovery also means a failure in mass recovery. As at fixed redshift, mismatches in SFH and degeneracies between age, dust and now also redshift cause underestimated ages, overestimated reddening and underestimated masses. Stellar masses are best determined at low redshift without reddening in the fit. Masses are then underestimated by only ∼0.1 dex whereas redshifts are similarly well recovered. Not surprisingly, the recovery of properties is substantially better for passive galaxies, for which e.g. the mass is recovered only slightly worse than at fixed redshift (underestimated by ∼0.02 dex instead of ∼0.01, at fixed IMF) using a setup including metallicity effects. In all cases, the recovery of physical parameters is crucially dependent on the wavelength coverage adopted in the fitting because the redshift recovery depends on the wavelength coverage. As is well known, redshifts are best recovered for a wavelength coverage including the Lyman and 4000 A break. As in Paper I, all effects from changing templates, the wavelength coverage and filters are quantified and scaling relations for the transformation of stellar masses obtained using different fitting parameters, including stellar population models, are provided.