Photometric Characterization of a Well-defined Sample of Isolated Galaxies in the Context of the AMIGA Project

Abstract

We perform a detailed photometric analysis (bulge–disc–bar decomposition and Concentration-Asymmetry-Clumpiness – CAS parametrization) for a well-defined sample of isolated galaxies, extracted from the Catalog of Isolated Galaxies and reevaluated morphologically in the context of the Analysis of the interstellar Medium of Isolated GAlaxies project. We focus on Sb–Sc morphological types, as they are the most representative population among the isolated spiral galaxies. Our analysis yields a large number of important galactic parameters and various correlation plots are used to seek relationships that might shed light on the processes involved in determining those parameters. Assuming that the bulge Sérsic index and/or bulge/total luminosity ratios are reasonable diagnostics for pseudo- versus classical bulges, we conclude that the majority of late-type isolated disc galaxies likely host pseudo-bulges rather than classical bulges. Our parametrization of galactic bulges and discs suggests that the properties of the pseudo-bulges are strongly connected to those of the discs. This may indicate that pseudo-bulges are formed through internal processes within the discs (i.e. secular evolution) and that bars may play an important role in their formation. Although the sample under investigation covers a narrow morphological range, a clear separation between Sb and Sbc–Sc types is observed in various measures, e.g. the former are redder, brighter, have larger discs and bars, more luminous bulges, are more concentrated, more symmetric and clumpier than the latter. A comparison with samples of spiral galaxies (within the same morphological range) selected without isolation criteria reveals that the isolated galaxies tend to host larger bars, are more symmetric, less concentrated and less clumpy.