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The empirical MILES stellar library is used to test the accuracy of three different, state-of-the-art, theoretical model libraries of stellar spectra. These models are widely used in the literature for stellar population analysis. A differential approach is used so that responses to elemental abundance changes are tested rather than absolute levels of the theoretical spectra. First we directly compare model line strengths and spectra to empirical data to investigate trends. Then we test how well line strengths match when element response functions are used to account for changes in [α/Fe] abundances. The aim is to find out where models best represent real star spectra, in a differential way, and hence identify good choices of models to use in stellar population analysis involving abundance patterns. We find that most spectral line strengths are well represented by these models, particularly iron and sodium sensitive indices. Exceptions include the higher order Balmer lines (Hδ, Hγ), in which the models show more variation than the data, particularly at low temperatures. C24668 is systematically underestimated by the models compared to observations. We find that differences between these models are generally less significant than the ways in which models vary from the data. Corrections to C2 line lists for one set of models are identified, improving them for future use.

The growth channel of massive galaxies involving mergers can be studied via close pairs as putative merger progenitors, where the stellar populations of the satellite galaxies will be eventually incorporated into the massive primaries. We extend our recent analysis of the GAMA-based sample of close pairs presented in Ferreras et al. to the general spectroscopic dataset of SDSS galaxies (DR14), for which the high S/N of the data enables a detailed analysis of the differences between satellite galaxies with respect to the mass of the primary galaxy. A sample of approximately two thousand satellites of massive galaxies is carefully selected within a relatively narrow redshift range (0.07

We explore the constraints that can be placed on the evolutionary timescales for typical low redshift galaxies evolving from the blue cloud through the green valley and onto the red sequence. We utilise galaxies from the GAMA survey with 0.1 < z < 0.2 and classify them according to the intrinsic (u* − r*) colours of their stellar populations, as determined by fits to their multi-wavelength spectral energy distributions. Using these fits to also determine stellar population ages and star formation timescales, we argue that our results are consistent with a green valley population dominated by galaxies that are simply decreasing their star formation (running out of gas) over a timescale of 2-4 Gyr which are seen at a specific epoch in their evolution (approximately 1.6 e-folding times after their peak in star formation). If their fitted star formation histories are extrapolated forwards, the green galaxies will further redden over time, until they attain the colours of a passive population. In this picture, no specific quenching event which cuts-off their star formation is required, though it remains possible that the decline in star formation in green galaxies may be expedited by internal or external forces. However, there is no evidence that green galaxies have recently changed their star formation timescales relative to their previous longer term star formation histories.

Unresolved gas and dust observations show a surprising diversity in the amount of interstellar matter in early-type galaxies. Using ALMA observations we resolve the ISM in z∼0.05 early-type galaxies. From a large sample of early-type galaxies detected in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) we selected five of the dustiest cases, with dust masses Md ∼several× 107M⊙, with the aim of mapping their submillimetre continuum and 12CO(2-1) line emission distributions. These observations reveal molecular gas disks. There is a lack of associated, extended continuum emission in these ALMA observations, most likely because it is resolved out or surface brightness limited, if the dust distribution is as extended as the CO gas. However, two galaxies have central continuum ALMA detections. An additional, slightly offset, continuum source is revealed in one case, which may have contributed to confusion in the Herschel fluxes. Serendipitous continuum detections further away in the ALMA field are found in another case. Large and massive rotating molecular gas disks are mapped in three of our targets, reaching a few× 109M⊙. One of these shows evidence of kinematic deviations from a pure rotating disc. The fields of our two remaining targets contain only smaller, weak CO sources, slightly offset from the optical galaxy centres. These may be companion galaxies seen in ALMA observations, or background objects. These heterogeneous findings in a small sample of dusty early-type galaxies reveal the need for more such high spatial resolution studies, to understand statistically how dust and gas are related in early-type galaxies.