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Register a new userInfrared Surface Brightness Analysis of Galaxies in Compact Groups
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Images of 7 Compact groups of galaxies (CG) were obtained using the 2.1m telescope in San Pedro Martir (B.C. Mexico) equipped with the NIR camera CAMILA. The NIR images trace the mass of the galaxies, through the oldest and more evolved stellar populations. The goal of this project is to search for evidence of morphological perturbations correlated with the level of activity (AGN or star formation) of the galaxies. We find that the level of perturbation is well correlated with activity observed in optical spectrocopy (Coziol et al. 2004). Evidence for perturbations decreases from more active groups to less active groups, confirming the classification. Our analysis suggests that galaxies in more active groups are undergoing important transformations due to interaction and merging and that the whole groups is on a merger path. Galaxies in less active CG have gone through similar processes in the recent past and are either in a final merging phase or in equilibrium due to a more massive halo of dark matter.
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We are using the 2dF spectrograph to make a survey of all objects (`stars and `galaxies) in a 12 sq.deg region towards the Fornax cluster. We have discovered a population of compact emission-line galaxies unresolved on photographic sky survey plates and therefore missing in most galaxy surveys based on such material. These galaxies are as luminous as normal field galaxies. Using H-alpha to estimate star formation they contribute at least an additional 5 per cent to the local star formation rate.
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Bayesian statistical calculations and linear-bisector calculations for obtaining Cepheid distances and radii by the infrared surface brightness method have been compared for a set of 38 Cepheids. The distances obtained by the two techniques agree to 1.5%+/-0.6% and the radii agree to 1.1%+/-0.7%. Thus the two methods yield the same distances and radii at the 2 sigma level. This implies that the short distance to the LMC found in recent linearbisector studies of Cepheids is not a result of simplifications in the mathematical approach. The computed uncertainties in distance and radius are larger in the Bayesian calculation typically by a factor of three.
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