Abstract
ABSTRACTWe present spherical, nonrotating, isotropic models of early-type galaxies with stellar and dark-matter components both described by deprojected Sérsic density profiles and prove that they represent physically admissible stable systems. Using empirical correlations and recent results of N-body simulations, all the free parameters of the models are expressed as functions of one single quantity: the total (B-band) luminosity of the stellar component. We analyze how to perform discrete N-body realizations of Sérsic models. To this end, an optimal smoothing length is derived, defined as the softening parameter minimizing the error on the gravitational potential for the deprojected Sérsic model. It is shown to depend on the Sérsic index n and on the number of particles of the N-body realization. A software code allowing the computations of the relevant quantities of one- and two-component Sérsic models is provided. Both the code and the results of the present work are primarily intended as tools to perform N-body simulations of early-type galaxies, where the structural nonhomology of these systems (i.e., the variation of the shape parameter along the galaxy sequence) might be taken into account.
Highlights
Merging of red-sequence galaxies might be an important channel for the formation of massive early-type galaxies (ETGs).Such dry mergers have been observed to take place and have an impact on the population of ETGs at both low, and intermediate redshift, in cluster and field environments
A further evidence comes from the fact that the stellar mass on the red sequence has been found to be nearly doubled from z ∼ 1 (Zucca et al 2006; Bell et al 2004) on, implying that at least some red galaxies must be formed from merging systems that are either very dusty or gas-poor (Faber et al 2005)
Using semi-analytical models, Khochfar & Burkert (2003) found that a large fraction of present-day ETGs are formed by merging bulge-dominated systems and that the fraction of spheroidal mergers increases with luminosity, with massive ETGs being formed by nearly dissipationless events
Summary
Merging of red-sequence galaxies might be an important channel for the formation of massive early-type galaxies (ETGs) Such dry mergers have been observed to take place and have an impact on the population of ETGs at both low Component is described by simple analytic density laws, such as the King or the Hernquist profiles This approach implicitly neglects one key observational feature: the structural non-homology of the ETG population (Graham & Colless 1997). The models describe spherical, non-rotating, isotropic systems, and are intended as a tool to perform N-body simulations of ETGs. In a companion contribution (Coppola et al 2009b, in preparation), we use the S2 models to investigate how dissipation-less (major and minor) mergers affect the structural properties of ETGs, such as the shape of their light profile and their stellar population gradients.
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