Although the stellar initial mass function (IMF) has only been directly determined in star clusters it has been manifoldly applied on galaxy-wide scales. But taking the clustered nature of star formation into account the galaxy-wide IMF is constructed by adding all IMFs of all young star clusters leading to an integrated galactic initial mass function (IGIMF). The IGIMF is top-light compared to...

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F450W (∼B) and F555W (∼V ) of the intermediate-age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416, and Kron 3 in the Small Magellanic Cloud. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of t...

We have used optical spectroscopy to investigate the active galaxy populations in a sample of 20 nearby Abell clusters. The targets were identified on the basis of 1.4 GHz radio emission, which identifies them as either AGN or galaxies forming stars at rates comparable to or greater than that of the Milky Way. The spectra were used to characterize the galaxies via their emission and absorption ...

We investigate how the [OII] properties and the morphologies of galaxies in clusters and groups at z = 0.4− 0.8 depend on projected local galaxy density. We also compare our results with those derived from the field at similar redshifts and from clusters at low-z. In both nearby and distant clusters, higher-density regions contain proportionally fewer star-forming galaxies. At odds with low-z r...

We investigate the stellar populations in the star forming ring of the luminous infrared galaxy NGC 7469. We use Hubble Space Telescope multi-wavelength (UV through NIR) imaging complemented with new K-band ground-based long-slit spectroscopy, and mid-IR and radio maps from the literature. Spectral energy distributions (SEDs) and evolutionary synthesis models have been used to characterize the ...

We present WFPC2 images in the F450W, F606W and F814W filters of the interacting pair of galaxies NGC 454. Our data indicate that the system is in the early stages of interaction. A population of young star-clusters has formed around the late component, and substantial amounts of gas have sunk into the center of the earlier component, where it has not yet produced significant visible star forma...

We investigate the variation of current star formation in galaxies as a function of distance along three supercluster filaments, each joining pairs of rich clusters, in the Pisces-Cetus supercluster, which is part of the two-degree Field Galaxy Redshift Survey (2dFGRS). We find that even though there is a steady decline in the rate of star formation, as well as in the fraction of star forming g...

Star cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populati...

We use HST/ACS imaging of 100 early-type galaxies in the ACS Virgo Cluster Survey to investigate the nature of diffuse star clusters (DSCs). Compared to globular clusters (GCs), these star clusters have moderately low luminosities (MV > −8) and a broad distribution of sizes (3 < rh < 30 pc), but they are principally characterized by their low mean surface brightnesses which can be more than thr...

We present the results of a Hubble Space Telescope WFPC2 F555W and F814W survey of 69 dwarf elliptical galaxies (dEs) in the Virgo and Fornax Clusters and Leo Group. The V − I colors of the dE globular clusters, nuclei, and underlying field star populations are used to trace the dE star-formation histories. We find that the dE globular cluster candidates are as blue as the metal-poor globular c...