Inside-out quenching Outside-in quenching PS ridge −0.5 0.0 0.5 1.0 log EW(Hα) 0.002 0.004 0.006 L′(Hα) 1.5 2.0 2.5 3.0 D4000 ●Twice as frequent in globally passive systems than in globally active systems: → in line with simulations of ring formation via captures of small satellites ([1], [3]). ● α"emission in the rings of the globally active S0s is 4 times higher than in those globally passive, implying: →star formation feeds on the gas of the host, → in"plain rings. 0.0 0.5 1.0 log EW(Hα) 0.00025 0.00050 0.00075 L′(Hα) 1.8 2.0 2.2 D4000 PS PCA of spectral profiles of ~500 S0 MaNGA galaxies. Radial binning and stacking of spaxels to generate the spectral profile of each galaxy, i. e., the mean spectrum as a function of the galactocentric distance. Projection of the spectral profiles onto their first 2 principal components (~90% of the sample variance [4]). José L. Tous1, Jaime D. Perea2, José M. Solanes1, elena Domínguez Sánchez3 ¹Institut de Ciències del Cosmos, Universitat de Barcelona (ICCUB), ² Instituto de Astrofísica de Andalucía (IAA"CSIC) , ³ Instituto de Ciencias del Espacio (ICE"CSIC) The examination of the spatially resolved IFS maps in a sample of more than 500 lenticular (S0) galaxies drawn from the MaNGA survey has unveiled the existence of transient inner annular structures (⟨R⟩ 1 R ∼ 1 R e) betraying ongoing star formation in a good number of these objects. Activity gradients in these galaxies have been measured through a novel methodology based on the principal component analysis of their optical spectra averaged over bins of galactocentric radius. We find that the sign of these gradients is closely linked to the presence of rings in the spectral maps, which are specially conspicuous in the equivalent width of α"emission, EW( α), with a fractional abundance —22–37% depending on the strictness of ring identification— larger than that inferred from optical imaging. While the numbers of S0s with globally positive, negative, and flat activity gradients are comparable, star"forming rings are found almost exclusively in objects with a positive slope for which quenching proceeds inside"out, in good agreement with predictions from cosmological simulations studying S0 buildup. The assessment of these structures and the properties of the galaxies harboring them also indicates that the frequency of such rings increases with the mass of their hosts, that they feed mainly on the gas from the disks, that are more short"lived in galaxies with ongoing star formation, and that the local environment does not play a relevant role in their formation. From the present analysis, we conclude that the presence of rings in the EW of the α emission line is a common phenomenon among fully formed S0s, possibly associated with annular disk resonances driven by weakly disruptive mergers preferentially involving the more massive representatives of these galaxies and their smaller and closer satellites. – ACKNOWLEDGMENTS: Financial support from the Spanish state agency MCIN/AEI/10.13039/501100011033 and ERDF through the grants: PID2019–106027GB–C41, PID2019–106027GB–C43, PRE2020–091838 and PID2020"115098RJ"I00. 1 Put a ring on it: the origin of star-forming rings in S0 galaxies The closer to the PS in the PC1–PC2 plane, the weaker the activity (SF/AGN) [2]. Vectorization and quenching classification. Profiles are converted into vectors. Then, galaxies are classified according to the orientation of these vectors wrt the PS ridge. This orientation establishes how quenching proceeds in galaxies. 2 Uniform SF Uniform SF Star-forming rings are common in S0 galaxies (20% to 40%) and are almost exclusively found in galaxies with inside-out profiles. 3 Implications: → the gas hinders the formation of rings, → the captured satellites must be tiny galaxies. The ring fraction increases with stellar mass. No dependence with environment. 4 REFERENCES: [1] Deeley, S., Drinkwater, M. J., Sweet, S. M., et al. 2021, MNRAS, 508, 895, 2021MNRAS.508..895D; [2]