The stellar mass assembly of galaxies can be affected by both secular and environmental processes. In this study, for the first time, we investigate the stellar mass assembly of $\sim90,000$ low redshift, central galaxies selected from SDSS group catalogues (M$_{\rm Stellar}\gtrsim10^{9.5}$M$_{\odot}$, M$_{\rm Halo}\gtrsim10^{12}$M$_{\odot}$) as a function of both stellar and halo mass. We use estimates of the times at which 10, 50 and 90 per cent of the stellar mass was assembled from photometric spectral energy distribution fitting, allowing a more complete investigation than single stellar ages alone. We consider trends in both stellar and halo mass simultaneously, finding dependencies of all assembly times on both. We find that galaxies with higher stellar masses (at constant halo mass) have on average older lookback times, similar to previous studies of galaxy assembly. We also find that galaxies at higher halo mass (at constant stellar mass) have younger lookback times, possibly due to a larger reservoir of gas for star formation. An exception to this is a sub sample with high stellar-to-halo mass ratios, which are likely massive, field spirals. We compare these observed trends to those predicted by the TNG300 simulation, finding good agreement overall as a function of either stellar or halo mass. However, some differences in the assembly times (of up to $\sim 3$ Gyr) appear when considering both stellar and halo mass simultaneously, noticeably at intermediate stellar masses (M$_{\rm Stellar} \sim 10^{11}$ M$_{\odot}$). These discrepancies are possibly linked to the quenched fraction of galaxies and the kinetic mode AGN feedback implemented in TNG300.

中文翻译：

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SDSS和TNG300模拟中低红移、大质量、中央星系的恒星质量组装

星系的恒星质量组装会受到长期和环境过程的影响。在这项研究中，我们首次研究了从 SDSS 群目录 (M$_{\rm Stellar}\gtrsim10^{9.5}$M$ _{\odot}$, M$_{\rm Halo}\gtrsim10^{12}$M$_{\odot}$) 作为恒星和晕质量的函数。我们使用光度光谱能量分布拟合对 10%、50% 和 90% 的恒星质量进行组装的时间进行估计，从而可以进行比单独单个恒星年龄更完整的研究。我们同时考虑恒星和晕质量的趋势，找到所有组装时间对两者的依赖性。我们发现具有较高恒星质量（在恒定光晕质量下）的星系平均具有较旧的回溯时间，类似于之前对星系组装的研究。我们还发现具有较高晕质量（以恒定恒星质量）的星系具有更年轻的回溯时间，这可能是由于用于恒星形成的气体储量更大。一个例外是具有高恒星与晕质量比的子样本，这可能是巨大的场螺旋。我们将这些观察到的趋势与 TNG300 模拟预测的趋势进行比较，发现总体上作为恒星质量或晕质量的函数具有良好的一致性。然而，当同时考虑恒星和晕质量时，组装时间会出现一些差异（高达 $\sim 3$ Gyr），尤其是在中等恒星质量 (M$_{\rm Stellar} \sim 10^{11} $ M$_{\odot}$)。这些差异可能与星系的淬灭分数和 TNG300 中实施的动力学模式 AGN 反馈有关。