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Accurate photometric redshift (photo- z) estimation requires support from multiband observational data. However, in the actual process of astronomical observations and data processing, some sources may have missing observational data in certain bands for various reasons. This could greatly affect the accuracy and reliability of photo- z estimation for these sources, and even render some estimation methods unusable. The same situation may exist for the upcoming Chinese Space Station Telescope (CSST). In this study, we employ a deep learning method called generative adversarial imputation networks (GAIN) to impute the missing photometric data in CSST , aiming to reduce the impact of data missing on photo- z estimation and improve estimation accuracy. Our results demonstrate that using the GAIN technique can effectively fill in the missing photometric data in CSST. Particularly, when the data missing rate is below 30 per cent, the imputation of photometric data exhibits high accuracy, with higher accuracy in the g, r, i, z , and y bands compared to the NUV and u bands. After filling in the missing values, the quality of photo- z estimation obtained by the widely used easy and accurate Zphot from Yale (eazy) software is notably enhanced. Evaluation metrics for assessing the quality of photo- z estimation, including the catastrophic outlier fraction (f out), the normalized median absolute deviation (⁠|$\rm {\sigma _{NMAD}}$|⁠), and the bias of photometric redshift (bias), all show some degree of improvement. Our research will help maximize the utilization of observational data and provide a new method for handling sample missing values for applications that require complete photometry data to produce results. [ABSTRACT FROM AUTHOR]

Accurate estimation of photometric redshifts (photo- z) is crucial in studies of both galaxy evolution and cosmology using current and future large sky surveys. In this study, we employ Random Forest (RF), a machine learning algorithm, to estimate photo- z and investigate the systematic uncertainties affecting the results. Using galaxy flux and colour as input features, we construct a mapping between input features and redshift by using a training set of simulated data, generated from the Hubble Space Telescope Advanced Camera for Surveys (HST-ACS) and COSMOS catalogue, with the expected instrumental effects of the planned China Space Station Telescope (CSST). To improve the accuracy and confidence of predictions, we incorporate inverse variance weighting and perturb the catalogue using input feature errors. Our results show that weighted RF can achieve a photo- z accuracy of |$\rm \sigma _{NMAD}=0.025$| and an outlier fraction of |$\rm \eta =2.045\ \hbox{per cent}$|⁠ , significantly better than the values of |$\rm \sigma _{NMAD}=0.043$| and |$\rm \eta =6.45\ \hbox{per cent}$| obtained by the widely used Easy and Accurate Zphot from Yale (EAZY) software, which uses template-fitting method. Furthermore, we have calculated the importance of each input feature for different redshift ranges and found that the most important input features reflect the approximate position of the break features in galaxy spectra, demonstrating the algorithm's ability to extract physical information from data. Additionally, we have established confidence indices and error bars for each prediction value based on the shape of the redshift probability distribution function, suggesting that screening sources with high confidence can further reduce the outlier fraction. [ABSTRACT FROM AUTHOR]

The accuracy of galaxy photometric redshift (photo- z) can significantly affect the analysis of weak gravitational lensing measurements, especially for future high-precision surveys. In this work, we try to extract photo- z information from both galaxy flux and image data expected to be obtained by China Space Station Telescope (CSST) using neural networks. We generate mock galaxy images based on the observational images from the Advanced Camera for Surveys of Hubble Space Telescope (HST -ACS) and COSMOS catalogues, considering the CSST instrumental effects. Galaxy flux data are then measured directly from these images by aperture photometry. The multilayer perceptron (MLP) and convolutional neural network (CNN) are constructed to predict photo- z from fluxes and images, respectively. We also propose to use an efficient hybrid network, which combines the MLP and CNN, by employing the transfer learning techniques to investigate the improvement of the result with both flux and image data included. We find that the photo- z accuracy and outlier fraction can achieve σNMAD = 0.023 and |$\eta = 1.43{{\ \rm per\ cent}}$| for the MLP using flux data only, and σNMAD = 0.025 and |$\eta = 1.21{{\ \rm per\ cent}}$| for the CNN using image data only. The result can be further improved in high efficiency as σNMAD = 0.020 and |$\eta = 0.90{{\ \rm per\ cent}}$| for the hybrid transfer network. These approaches result in similar galaxy median and mean redshifts 0.8 and 0.9, respectively, for the redshift range from 0 to 4. This indicates that our networks can effectively and properly extract photo- z information from the CSST galaxy flux and image data. [ABSTRACT FROM AUTHOR]