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We report the results of Gemini/GMOS long-slit spectroscopic observationsalong the major and minor axes of the central galaxies in two fossil groups,SDSS J073422.21+265133.9 and SDSS J075828.11+374711.8 (the NGC 2484 group).Spatially resolved kinematics and stellar population parameters (ages,metallicities and $\alpha$-element abundance ratios) derived using ~20 Lickindices are presented. Despite remarkable similarities in their morphologies,photometric properties (luminosity and colour) and kinematics, the two galaxiesexhibit significantly different stellar population parameters.  SDSS J073422.21+265133.9 exhibits a strong metallicity gradient(Delta[Z/H]/Delta R ~ -0.4) all the way into the centre of the galaxy. It alsoexhibits an age profile that suggest a relatively recent, centrallyconcentrated burst of star formation superimposed on an older, more spatiallyextended population. NGC 2484, a well known X-ray AGN, exhibits a flatcore-like structure in its metallicity gradient, but no detectable agegradient. The alpha-element abundance ratio ([E/Fe]) profiles of the twogalaxies are also significantly different. SDSS J073422.21+265133.9 exhibits aslightly positive gradient (Delta [E/H]/Delta R ~ 0.1), perhaps againsuggesting a more recent central burst of star formation, while NGC 2484 showsa negative gradient (Delta [E/H]/Delta R ~-0.1), indicating that star formationmay have happened "inside out".  Our analysis of these two galaxies of similar mass, morphology and kinematicstherefore suggests two different mechanisms to have been in action during theirformation. Consequently, we conclude that the central galaxies of fossil groupscan not be considered a homogeneous group with regard to their formationprocesses or star formation histories.

Spatially resolved stellar population parameters in the BCGs of two fossil groups