2023MNRAS.519.1476A

We investigate how the environment affects the assembly history of massive galaxies. For that purpose, we make use of Survey for High-z Absorption Red and Dead Sources (SHARDS) and HST spectrophotometric data, whose depth, spectral resolution, and wavelength coverage allow to perform a detailed analysis of the stellar emission as well as obtaining unprecedentedly accurate photometric redshifts. This expedites a sufficiently accurate estimate of the local environment and a robust derivation of the star formation histories of a complete sample of 332 massive galaxies (>10¹⁰M_⊙) at redshift 1 ≤ z ≤ 1.5 in the GOODS-N field. We find that massive galaxies in this redshift range avoid the lowest density environments. Moreover, we observed that the oldest galaxies in our sample with mass-weighted formation redshift $\mathrm{\overline{z}_{M-w} \ge 2.5}$, avoid the highest density regions, preferring intermediate environments. Younger galaxies, including those with active star formation, tend to live in denser environments ($\Sigma = \mathrm{5.0_{1.1}^{24.8}\times 10^{10}\, M_{\odot }\, Mpc^{-2}}$). This behaviour could be expected if those massive galaxies starting their formation first would merge with neighbours and sweep their environment earlier. On the other hand, galaxies formed more recently ($\overline{z}_{M-w} \lt 2.5$) are accreted into large-scale structures at later times and we are observing them before sweeping their environment or, alternatively, they are less likely to affect their environment. However, given that both number and mass surface densities of neighbour galaxies is relatively low for the oldest galaxies, our results reveal a very weak correlation between environment and the first formation stages of the earliest massive galaxies.