http://arxiv.org/abs/2208.14084

(Abridged) We study the distribution of galaxies across the ageing diagram (AD): the connection between the fraction of stars formed during the last few Myr — traced by EW(H$\alpha$) — and the amount of stellar mass formed on scales of ~Gyr — using the dust-corrected optical colour $(g-r)_0$ or the Balmer break $D_n(4000)$ as observational proxies. By means of this diagram, it is possible to track recent changes on the star formation history (SFH) of galaxies and discriminate between galaxies governed by secular evolution (ageing) and systems whose star formation was suddenly interrupted (quenching). In order to provide a physical characterization of the location of galaxies across the AD, we use Pipe3D estimates of the SFH of two galaxy samples selected from the CALIFA and MaNGA surveys, in combination with the predictions from IllustrisTNG. We find that the distribution of galaxies in the AD can be described by four regimes, that strongly correlate with the stellar mass fractions formed in the last 300 Myr and 3 Gyr. Ageing systems, whose star formation rate changes on scales comparable to the age of the Universe, account for $70-80\%$ of the galaxy population in all our samples. Objects whose SFH was abruptly truncated arrange along a detached Quenched sequence that represents $\sim 5-10\%$ by (volume-corrected) number. Undetermined systems represent an intermediate population between the Ageing and Quenched regimes. Finally, Retired galaxies are located at the region in the AD where the Ageing and Quenched sequences converge. We define different star formation activity levels in terms of the birth rate parameter $b\equiv \frac{SFR}{\langle SFR \rangle}$ and find that galaxies transit from the Ageing to the Quenched sequence on scales ~500 Myr. We conclude that the ageing diagram provides a useful tool to discern recently Quenched galaxies from the dominant Ageing population.

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P. Corcho-Caballero, Y. Ascasibar, S. Sánchez, et. al.
Wed, 31 Aug 22
25/86

Comments: Submitted to MNRAS. Comments welcome!