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