Euclid preparation: LXXXI. The impact of nonparametric star formation histories on spatially resolved galaxy property estimation using synthetic Euclid images

Abstract

We analyzed the spatially resolved and global star formation histories (SFHs) for a sample of 25 TNG50-SKIRT Atlas galaxies to assess the feasibility of reconstructing accurate SFHs from Euclid-like data. This study provides a proof of concept for extracting the spatially resolved SFHs of local galaxies with Euclid, highlighting the strengths and limitations of SFH modeling in the context of next-generation galaxy surveys. We used the spectral energy distribution (SED) fitting code Prospector to model both spatially resolved and global SFHs using parametric and nonparametric configurations. The input consisted of mock ultraviolet--near-infrared photometry derived from the TNG50 cosmological simulation and processed with the radiative transfer code SKIRT. We show that nonparametric SFHs provide a more effective approach to mitigating the outshining effect by recent star formation, offering improved accuracy in the determination of galaxy stellar properties. Also, we find that the nonparametric SFH model at resolved scales closely recovers the stellar mass formation times (within 0.1~dex) and the ground truth values from TNG50, with an absolute average bias of $0.03$~dex in stellar mass and $0.01$~dex in both specific star formation rate and mass-weighted age. In contrast, larger offsets are estimated for all stellar properties and formation times when using a simple $τ$-model SFH, at both resolved and global scales, highlighting its limitations. These results emphasize the critical role of nonparametric SFHs in both global and spatially resolved analyses, as they better capture the complex evolutionary pathways of galaxies and avoid the biases inherent in simple parametric models.

Figures (12)

• Figure 1: SFR as a function of $M_\star$ for the TNG50- SKIRT Atlas galaxies at $z = 0$. Galaxies are separated as star-forming (blue stars) and quiescent (red points) based on their sSFR. The dashed orange line indicates this separation between star formation and quiescence (sSFR = $10^{-11}$ yr$^{-1}$). The black squares indicate the selected sample of 25 galaxies used in our analysis.
• Figure 2: Example of a simulated galaxy processed with piXedfit. We show the synthetic images of GALEX, LSST, and for TNG275545 with the O1 orientation index. Observational effects were introduced to the original synthetic images from the TNG50- SKIRT Atlas database in the form of simulated noise and convolution with the PSF of the corresponding cameras. The FWHM of the PSF as well as the pixel size of the images are $5\arcsecf05$ and $1\arcsecf5$, respectively. The pixels are binned with piXedfit to increase the S/N of the spatially resolved SEDs.
• Figure 3: Examples of the stellar property maps of five TNG50- SKIRT Atlas galaxies, obtained from the spatially resolved SED fitting of GALEX, LSST, and photometry with Prospector. The maps include the stellar mass surface density ($\Sigma_\star$), the SFR surface density ($\Sigma_\mathrm{SFR}$), stellar metallicity ($Z_\star$), and mass-weighted stellar age ($t_\mathrm{\star,\,mw}$). Next to each galaxy’s sub-halo ID, we indicate whether a galaxy is classified as star-forming (SF) or quiescent (Q), based on its global sSFR.
• Figure 4: Examples of residual maps of the stellar properties of two TNG50- SKIRT Atlas galaxies, obtained from the nonparametric SFH configuration. The residual maps include the stellar mass surface density ($\Sigma_\star$), the SFR surface density ($\Sigma_\mathrm{SFR}$), stellar metallicity ($Z_\star$), and mass-weighted stellar age ($t_\mathrm{\star,\,mw}$). Each residual map is computed as the logarithmic ratio of the inferred property from Prospector to the ground truth value from TNG50, expressed as $\logten$( Prospector/TNG50).
• Figure 5: Comparisons of the spatially resolved stellar population properties for 6958 pixel bins in the 25 sample galaxies derived from spatially resolved SED fitting with a nonparametric SFH model. The depicted physical properties include the stellar mass surface density ($\Sigma_\star$), the SFR surface density ($\Sigma_\mathrm{SFR}$), the stellar metallicity ($Z_\star$), and the mass-weighted stellar age ($t_\mathrm{\star,\,mw}$). The colors indicate the average trend with the dust optical depth in the $V$ band ($\hat{\tau}_\mathrm{dust,\, 2}$), calculated with the LOESS method. Each hexbin includes a minimum of five points. Contours enclose 20%, 50%, and 80% of the total data. The dashed orange line represents the one-to-one relation. The Spearman’s correlation coefficient ($\rho$), measured bias (average offset $\mu$), and scatter (standard deviation $\sigma$) relative to the ground truth from TNG50 are indicated in the legend of each panel.