Title: Observational evidence of galaxy assembly bias,
Abstract: We analyze the spectra of 300,000 luminous red galaxies (LRGs) with stellar
masses $M_* \gtrsim 10^{11} M_{\odot}$ from the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS). By studying their star-formation histories, we
find two main evolutionary paths converging into the same quiescent galaxy
population at $z\sim0.55$. Fast-growing LRGs assemble $80\%$ of their stellar
mass very early on ($z\sim5$), whereas slow-growing LRGs reach the same
evolutionary state at $z\sim1.5$. Further investigation reveals that their
clustering properties on scales of $\sim$1-30 Mpc are, at a high level of
significance, also different. Fast-growing LRGs are found to be more strongly
clustered and reside in overall denser large-scale structure environments than
slow-growing systems, for a given stellar-mass threshold. Our results imply a
dependence of clustering on stellar-mass assembly history (naturally connected
to the mass-formation history of the corresponding halos) for a homogeneous
population of similar mass and color, which constitutes a strong observational
evidence of galaxy assembly bias.