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The counter-rotation phenomenon in disc galaxies directly indicates a complexgalaxy assembly history which is crucial for our understanding of galaxyphysics. Here we present the complex data analysis for a lenticular galaxy NGC448, which has been recently suspected to host a counter-rotating stellarcomponent. We collected deep long-slit spectroscopic observations using theRussian 6-m telescope and performed the photometric decomposition of SloanDigital Sky Survey (SDSS) archival images. We exploited (i) a non-parametricapproach in order to recover stellar line-of-sight velocity distributions and(ii) a parametric spectral decomposition technique in order to disentanglestellar population properties of both main and counter-rotating stellar discs.Our spectral decomposition stays in perfect agreement with the photometricanalysis. The counter-rotating component contributes $\approx$30 per cent tothe total galaxy light. We estimated its stellar mass to be$9.0^{+2.7}_{-1.8}\cdot10^{9}M_\odot$. The radial scale length ofcounter-rotating disc is $\approx$3 times smaller than that of the main disc.Both discs harbour old stars but the counter-rotating components reveals adetectable negative age gradient that might suggest an extended inside-outformation during $3\dots4$ Gyrs. The counter-rotating disc hosts moremetal-rich stars and possesses a shallower metallicity gradient with respect tothe main disc. Our findings rule out cosmological filaments as a source ofexternal accretion which is considered as a potential mechanism of thecounter-rotating component formation in NGC 448, and favour the satellitemerger event with the consequent slow gas accretion.

Stellar counter-rotation in lenticular galaxy NGC 448