Resolving galaxies in time and space: II: Uncertainties in the spectral synthesis of datacubes

TL;DR

This paper evaluates the uncertainties in spectral synthesis products derived from CALIFA galaxy datacubes, considering noise, calibration errors, synthesis methods, and model choices, and discusses their impact on stellar population properties.

Contribution

It systematically assesses the sources of uncertainties in spectral synthesis of datacubes, including noise, calibration, and model selection, providing a comprehensive error analysis.

Findings

Uncertainties in stellar masses, ages, and metallicities are 0.10-0.15 dex due to noise and calibration errors.

Shape errors increase uncertainties in A_V to 0.16 mag, higher than random noise.

Spatial averaging reduces uncertainties in radial profiles and star formation histories.

Abstract

In a companion paper we have presented many products derived from the application of the spectral synthesis code STARLIGHT to datacubes from the CALIFA survey, including 2D maps of stellar population properties and 1D averages in the temporal and spatial dimensions. Here we evaluate the uncertainties in these products. Uncertainties due to noise and spectral shape calibration errors and to the synthesis method are investigated by means of a suite of simulations based on 1638 CALIFA spectra for NGC 2916, with perturbations amplitudes gauged in terms of the expected errors. A separate study was conducted to assess uncertainties related to the choice of evolutionary synthesis models. We compare results obtained with the Bruzual & Charlot models, a preliminary update of them, and a combination of spectra derived from the Granada and MILES models. About 100k CALIFA spectra are used in this comparison. Noise and shape-related errors at the level expected for CALIFA propagate to 0.10-0.15 dex uncertainties in stellar masses, mean ages and metallicities. Uncertainties in A_V increase from 0.06 mag in the case of random noise to 0.16 mag for shape errors. Higher order products such as SFHs are more uncertain, but still relatively stable. Due to the large number statistics of datacubes, spatial averaging reduces uncertainties while preserving information on the history and structure of stellar populations. Radial profiles of global properties, as well as SFHs averaged over different regions are much more stable than for individual spaxels. Uncertainties related to the choice of base models are larger than those associated with data and method. Differences in mean age, mass and metallicity are ~ 0.15 to 0.25 dex, and 0.1 mag in A_V. Spectral residuals are ~ 1% on average, but with systematic features of up to 4%. The origin of these features is discussed. (Abridged)