We investigate the luminosity–metallicity (L–Z) relation in the local Universe (0 < z < 0.15) using spectra of 6387 star‐forming galaxies extracted from the 2dF Galaxy Redshift Survey. This sample is by far the largest to date used to perform such a study. We distinguish star‐forming galaxies from active galactic nuclei (AGNs) using ‘standard’ diagnostic diagrams to build a homogeneous sample of starburst galaxies for the L–Z study. We propose new diagnostic diagrams using ‘blue’ emission lines ([O ii]λ3727, [O iii]λ5007 and Hβ) only to discriminate starbursts from AGNs in intermediate‐redshift (z > 0.3) galaxies. Oxygen‐to‐hydrogen (O/H) abundance ratios are estimated using the ‘strong‐line’ method, which relates the strength of following bright emission lines [O ii]λ3727, [O iii]λ5007 and Hβ (parameters R23 and O32) to O/H. We used the [N ii]λ6584/Hα emission‐line ratio as a ‘secondary’ abundance indicator to break the degeneracy between O/H and R23. We confirm the existence of the L–Z relation over a large range of abundances (∼2 dex) and luminosities (∼9 mag). We find a linear relation between the gas‐phase oxygen abundance and both the ‘raw’ and extinction‐corrected absolute B‐band magnitude with a rms of ∼0.27. A similar relation, with nearly the same scatter, is found in the R band. This relation is in good agreement with that derived by Melbourne and Salzer using the Kitt Peak National Observatory (KPNO) International Spectroscopic Survey (KISS) data. However, our L–Z relation is much steeper than previous determinations using samples of ‘normal’ irregular and spiral galaxies. This difference seems to be primarily due to the choice of the galaxy sample used to investigate the L–Z relation rather than any systematic error affecting the O/H determination. We anticipate that this L–Z relation will be used as the local ‘reference’ for future studies of the evolution with cosmic time of fundamental galaxy scaling relations.

We have recently identified a new radial migration mechanism resulting from the overlap of spiral and bar resonances in galactic disks. Here we confirm the efficiency of this mechanism in fully self-consistent, Tree-SPH simulations, as well as high-resolution pure N-body simulations. In all barred cases we clearly identify the effect of spiral-bar resonance overlap by measuring a bimodality in the changes of angular momentum in the disk, ΔL, whose maxima are near the bar's corotation and outer Lindblad resonance. This contrasts with the smooth distribution of ΔL for a simulation with no stable bar present, where strong radial migration is induced by multiple spirals. The presence of a disk gaseous component appears to increase the rate of angular momentum exchange by about 20%. The efficiency of this mechanism is such that galactic stellar disks can extend to over 10 scale-lengths within 1-3 Gyr in both Milky Way size and low-mass galaxies (circular velocity ∼100 km s −1 ). We also show that metallicity gradients can flatten in less than 1 Gyr rendering mixing in barred galaxies an order of magnitude more efficient than previously thought.

We have used new deep observations of the Coma cluster from Galaxy Evolution Explorer to visually identify 13 star-forming galaxies with asymmetric morphologies in the ultraviolet (UV). Aided by wide-field optical broad-band and Hα imaging, we interpret the asymmetric features as being due to star formation within gas stripped from the galaxies by interaction with the cluster environment. The selected objects display a range of structures from broad fanshaped systems of filaments and knots ('jellyfish') to narrower and smoother tails extending up to 100 kpc in length. Some of the features have been discussed previously in the literature, while others are newly identified here. We assess the ensemble properties of the sample. The candidate stripping events are located closer to the cluster centre than other star-forming galaxies; their radial distribution is more similar to that of all cluster members, dominated by passive galaxies. The fraction of blue galaxies which are undergoing stripping falls from 40 per cent in the central 500 kpc to less than 5 per cent beyond 1 Mpc. We find that tails pointing away from (i.e. galaxies moving towards) the cluster centre are strongly favoured (11/13 cases). From the small number of 'outgoing' galaxies with stripping signatures, we conclude that the stripping events occur primarily on first passage towards the cluster centre, and are short-lived compared to the cluster crossing time. Using galaxy infall trajectories extracted from a cosmological simulation, we find that the observed fraction of blue galaxies undergoing stripping can be reproduced if the events are triggered at a threshold radius of ∼1 Mpc and detectable for ∼500 Myr. Hubble Space Telescope images are available for two galaxies from our sample and reveal compact blue knots coincident with UV and Hα emission, apparently forming stars within the stripped material. Our results confirm that stripping of gas from infalling galaxies, and associated star formation in the stripped material, is a widespread phenomenon in rich clusters. Deep UV imaging of additional clusters is a promising route to constructing a statistically powerful sample of stripping events and constraining models for the truncation of star formation in clusters.