The photometric evolution of galaxies in a hierarchically clustering universe is investigated. The study is based on high-resolution numerical simulations that include the e †ects of gasdynamics, shock heating, radiative cooling, and a heuristic star formation scheme. The outcome of the simulations is convolved with photometric models, which enables us to predict the appearance of galaxies in the broadband colors U, B, V , R, I, and K. We demonstrate the e †ect of the mutual interplay of the hierarchical buildup of galaxies, photometric evolution, k-correction, and intervening absorption on the appearance of forming disk galaxies at redshift 1È3. We also discuss to what extent the numerical resolution of current computer simulations is sufficient to make quantitative predictions on surface density proÐles and color gradients.
We define a Tidal Dwarf Galaxy (TDG) as a self-gravitating entity of dwarf-galaxy mass built from tidal material expelled during interactions. We summarize our findings on broad-band imaging and spectroscopy of a sample of Tidal Dwarf Galaxies candidates in a sequence of interacting systems. Evidence for decoupled kinematics in the ionized gas have been found in several objects. This could indicate that they are bound galaxies and therefore genuine TDGs.As a detailed example we analyze the system AM 1159-530, where surprisingly high velocity gradients have been measured.
The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2006.10757.
The galaxy population in rich local galaxy clusters shows a ratio of one quarter elliptical galaxies, two quarters S0 galaxies, and one quarter spiral galaxies. Observations of clusters at redshift 0.5 show a perspicuously different ratio, the dominant galaxy type are spiral galaxies with a fraction of two quarters while the number of S0 galaxies decreases to a fraction of one quarter (Dressler et al. 1997). This shows an evolution of the galaxy population in clusters since redshift 0.5 and it has been suspected that galaxy transformation processes during the infall into a cluster are responsible for this change. These could be merging, starburst or rampressure stripping. We use our evolutionary synthesis models to describe various possible effects of those interactions on the star formation of spiral galaxies infalling into clusters. We study the effects of starbursts of various strengths as well as of the truncation of star formation at various epochs on the color and luminosity evolution of model galaxies of various spectral types. As a first application we present the comparison of our models with observed properties of the local S0 galaxy population to constrain possible S0 formation mechanisms in clusters. Application to other types of galaxies is planned for the future.
This paper is part of a series devoted to a detailed analysis of the properties of the compact group CG J1720-67.8 and its member galaxies with the aim of shedding light on its evolutionary history. Here we interpret our previously published observational results through comparison with chemically consistent spectrophotometric evolutionary synthesis models to gain further clues to the evolution of the galaxies in this group. In order to reduce the number of free parameters, we considered the simplest case of a single burst of star-formation turned on after 11−12 Gyr of undisturbed galaxy evolution. However, we also briefly explored the effect of multiple, interaction-induced bursts of star-formation. We found that the two spiral galaxies are consistent with interaction-induced strong starbursts switched on ∼40 to 180 Myr ago and still active. For the early-type galaxy, a < ∼ 0.9−1.3 Gyr old star-formation event (depending on the considered model) appears consistent with the observed properties. The comparison with models cannot rule out the possibility that this galaxy is already the result of a merger. Alternatively, a starformation episode in this galaxy might have been triggered by gas inflow as a consequence of the interaction with the companion galaxies. Estimates of galaxy masses were derived from the comparison with the models. Finally our results are discussed in comparison with other well-studied, poor galaxy systems.
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