The role of E+A and post-starburst galaxies II. Spectral energy distributions and comparison with observations

In a previous paper (Falkenberg, Kotulla & Fritze 2009, astro-ph/0901.1665) we have shown that the classical definition of E+A galaxies excludes a significant number of post-starburst galaxies. We suggested that analysing broad-band spectral energy distributions (SEDs) is a more comprehensive method to select and distinguish poststarburst galaxies than the classical definition of measuring equivalent widths of (Hδ) and [O ii] lines. In this paper we will carefully investigate this new method and evaluate it by comparing our model grid of post-starburst galaxies to observed E+A galaxies from the MORPHS catalog. In a first part we investigate the UV/U-optical-NIR SEDs of a large variety in terms of progenitor galaxies, burst strengths and timescales of post-starburst models and compare them to undisturbed spiral, S0 and E galaxies as well as to galaxies in their starburst phase. In a second part we compare our post-starburst models with the observed E+A galaxies in terms of Lick indices, luminosities and colours. We then use the new method of comparing the model SEDs with SEDs of the observed E+A galaxies. We find that the post-starburst models can be distinguished from undisturbed spiral, S0 and E galaxies and galaxies in their starburst phase on the basis of their SEDs. It is even possible to distinguish most of the different post-starburst by their SEDs. From the comparison with observations we find that all observed E+A galaxies from the MORPHS catalog can be matched by our models. However only models with short decline timescales for the star formation rate are possible scenarios for the observed E+A galaxies in agreement with our results from the first paper (see Falkenberg, Kotulla & Fritze 2009a).