We have developed a computationally competitive N -body model of a previrialized aggregation of galaxies in a flat ΛCDM universe to assess the role of the multiple mergers that take place during the formation stage of such systems in the configuration of the remnants assembled at their centres. An analysis of a suite of 48 simulations of low-mass forming groups (M tot,gr ∼ 10 13 h −1 M ) demonstrates that the gravitational dynamics involved in their hierarchical collapse is capable of creating realistic firstranked galaxies without the aid of dissipative processes. Our simulations indicate that the brightest group galaxies (BGGs) constitute a distinct population from other group members, sketching a scenario in which the assembly path of these objects is dictated largely by the formation of their host system. We detect significant differences in the distribution of Sérsic indices and total magnitudes, as well as a luminosity gap between BGGs and the next brightest galaxy that is positively correlated with the total luminosity of the parent group. Such gaps arise from both the grow of BGGs at the expense of lesser companions and the decrease in the relevance of secondranked objects in equal measure. This results in a dearth of intermediate-mass galaxies which explains the characteristic central dip detected in their luminosity functions in dynamically young galaxy aggregations. The fact that the basic global properties of our BGGs define a thin mass fundamental plane strikingly similar to that followed giant early-type galaxies in the local universe reinforces confidence in the results obtained.

Aims. We present an adaptation of the standard scenario of disk-galaxy formation to the concordant ΛCDM cosmology aimed to derive analytical expressions for the scale length and rotation speed of present-day disks that form within four different, cosmologically motivated protogalactic dark matter halo-density profiles. Methods. We invoke a standard galaxy-formation model that includes virial equilibrium of spherical dark halos, specific angular momentum conservation during gas cooling, and adiabatic halo response to the gas inflow. The mean mass-fraction and mass-to-light ratio of the central stellar disk are treated as free parameters whose values are tuned to match the zero points of the observed sizeluminosity and circular speed-luminosity relations of galaxies. Results. We supply analytical formulas for the characteristic size and rotation speed of disks built inside Einasto r 1/6 , Hernquist, Burkert, and Navarro-Frenk-White dark matter halos. These expressions match simultaneously the observed zero points and slopes of the different correlations that can be built in the RVL space of disk galaxies from plausible values of the galaxy-and star-formation efficiencies.

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This paper reports one recent result from a set of pre-virialized galaxy group simulations that are being used in an investigation of measurement techniques for the quantity of intragroup light (IGL). We present evidence that the binding energy of the stellar material stripped from the galaxies is essentially uncorrelated with the local mass density. This suggests that IGL detection methods based on the distribution of luminosity perform poorly in detecting the unbound stars.