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Drawing from the LEGA-C dataset, we present the spectroscopic view of thestellar population across a large volume- and mass-selected sample of galaxiesat large lookback time. We measure the 4000\AA\ break (D$_n$4000) and Balmerabsorption line strengths (probed by H$\delta$) from 1019 high-quality spectraof $z=0.6 - 1.0$ galaxies with $M_\ast = 2 \times 10^{10} M_\odot - 3 \times10^{11} M_\odot$. Our analysis serves as a first illustration of the power ofhigh-resolution, high-S/N continuum spectroscopy at intermediate redshifts as aqualitatively new tool to constrain galaxy formation models. The observedD$_n$4000-EW(H$\delta$) distribution of our sample overlaps with thedistribution traced by present-day galaxies, but $z\sim 0.8$ galaxies populatethat locus in a fundamentally different manner. While old galaxies dominate thepresent-day population at all stellar masses $> 2\times10^{10} M_\odot$, we seea bimodal D$_n$4000-EW(H$\delta$) distribution at $z\sim0.8$, implying abimodal light-weighted age distribution. The light-weighted age dependsstrongly on stellar mass, with the most massive galaxies$>1\times10^{11}M_\odot$ being almost all older than 2 Gyr. At the same time weestimate that galaxies in this high mass range are only $\sim3$ Gyr youngerthan their $z\sim0.1$ counterparts, at odd with pure passive evolution given adifference in lookback time of $>5$ Gyr; younger galaxies must grow to$>10^{11}M_\odot$ in the meantime, and/or small amounts of young stars mustkeep the light-weighted ages young. Star-forming galaxies at $z\sim0.8$ havestronger H$\delta$ absorption than present-day galaxies with the sameD$_n$4000, implying larger short-term variations in star-formation activity.

Stellar Populations of over one thousand $z\sim0.8$ Galaxies from LEGA-C: Ages and Star Formation Histories from D$_n$4000 and H$\delta$