We examine the environment of star-forming galaxies selected in the 2dFGRS. We find that bright star-forming galaxies display a significant deficit of faint neighbours relative to passive galaxies. If a deficit in fainter companions implies a smaller mass halo, data support a scenario predicting star-formation to be suppressed in all systems more massive than 1013M⊙, rather than in clusters only.

We demonstrate that the high pressure of the hot intracluster medium (ICM) can trigger the collapse of molecular clouds in a spiral galaxy, leading to a burst of star formation in the clouds. Our hydrodynamical simulations show that the high gaseous (ram pressure and static thermal) pressure of the ICM strongly compresses a self-gravitating gas cloud within a short time scale (∼ 10 yr), dramati...

Recent high-resolution observations with the Hubble Space Telescope (HST) reveal that star clusters of extraordinary luminosity and compactness are commonly found in a variety of starburst systems. There has been much speculation that these clusters represent present-day analogs of young globular clusters. Using the HIRES echelle spectrograph on the Keck 10 m telescope, we obtained high-dispers...

We present HST/NICMOS observations of a sample of LIRGs. We show that active star formation appears to be occurring not only in the bright nuclei of these galaxies, but also in luminous super-star clusters and giant H ii regions with ages of up to 20− 40Myr. This population of bright clusters and H ii regions is unprecedented in normal galaxies and emphasizes the effects of the extreme star for...

We have formed “composite spectra” by combining the integrated–light spectra of individual galaxies in 8 intermediate–redshift and 12 low–redshift clusters of galaxies. Because these composite spectra have much higher signal–to–noise ratios than individual galaxy spectra, they are particularly useful in quantifying general trends in star formation for galaxy populations in distant clusters, z >...

We model gravitational collapse leading to star formation in a wide range of isolated disk galaxies using a three-dimensional, smoothed particle hydrodynamics code. The model galaxies include a dark matter halo and a disk of stars and isothermal gas. Absorbing sink particles are used to directly measure the mass of gravitationally collapsing gas. They reach masses characteristic of stellar clus...

We demonstrate that single and binary star clusters can be formed during cloud-cloud collisions triggered by the tidal interaction between the Large and Small Magellanic clouds. We run two different sets of self-consistent numerical simulations which show that compact, bound star clusters can be formed within the centers of two colliding clouds due to strong gaseous shocks, compression, and dis...

We investigate the recent and current star formation activity of galaxies as function of distance from the cluster center in a sample of 521 SDSS clusters at z < 0.1. We characterize the recent star formation history by the strength of the 4000Å break and the strength of the Balmer absorption lines, and thus probe the star formation history over the last ∼ 2Gyr. We show that when the Brightest ...

Star clusters that form in nuclear rings appear to be at slightly larger radii than the gas. We argue that the star clusters move out from the gas in which they are formed because of satellite-disk tidal interactions. In calculating the dynamics of this star cluster and gas ring system, we include the effects of dynamical friction of the background stars in the host galaxy on the star cluster, ...

It is a longstanding and remarkable problem when and how red S0 galaxies were formed in clusters of galaxies. We here propose that the major mechanism for the S0 creation is galaxy merging between two spirals with unequal mass. Our numerical simulations demonstrate that galaxy merging exhausts a large amount of interstellar medium of two gas-rich spirals owing to the moderately enhanced star fo...