We present SKIRT (Stellar Kinematics Including Radiative Transfer), a new Monte Carlo radiative transfer code that allows the calculation of the observed stellar kinematics of a dusty galaxy. The code incorporates the effects of both absorption and scattering by interstellar dust grains, and calculates the Doppler shift of the emerging radiation exactly by taking into account the velocities of the emitting stars and the individual scattering dust grains. The code supports arbitrary distributions of dust through a cellular approach, whereby the integration through the dust is optimized by means of a novel efficient trilinear interpolation technique.We apply our modelling technique to calculate the observed kinematics of realistic models for dusty disc galaxies. We find that the effects of dust on the mean projected velocity and projected velocity dispersion are severe for edge-on galaxies. For galaxies which deviate more than a few degrees from exactly edge-on, the effects are already strongly reduced. As a consequence, dust attenuation cannot serve as a possible way to reconcile the discrepancy between the observed shallow slopes of the inner rotation curves of low surface brightness galaxies and the predictions of cold dark matter cosmological models. For face-on galaxies, the velocity dispersion increases with increasing dust mass owing to scattering, but the effects are limited, even for extended dust distributions. Finally, we show that serious errors can be made when the individual velocities of the dust grains are neglected in the calculations.

In order to investigate the nature of dwarf Low Surface Brightness (LSB) galaxies we have undertaken a deep B and I band CCD survey of a 14 sq degree strip in the Virgo Cluster and applied a Fourier convolution technique to explore its dwarf galaxy population down to a central surface brightness of ∼ 26 B mag/ arcsec 2 and a total absolute B mag of ∼ -10. In this paper we carry out an analysis of their morphology, (B-I) colours and atomic hydrogen content. We compare these properties with those of dwarf galaxies in other environments to try and assess how the cluster environment has influenced their evolution. Field dwarfs are generally of a more irregular morphology, are bluer and contain relatively more gas. We assess the importance that various physical processes have on the evolution of cluster dwarf galaxies (ram pressure stripping, tidal interactions, supernova driven gas loss). We suggest that enhanced star formation triggered by tidal interactions is the major reason for the very different general properties of cluster dwarfs: they have undergone accelerated evolution.

In order to investigate the nature of dwarf Low Surface Brightness (LSB) galaxies we have undertaken a deep B and I band CCD survey of a 14 sq degree strip in the Virgo Cluster and applied a Fourier convolution technique to explore its dwarf galaxy population down to a central surface brightness of ∼ 26 B mag/ arcsec 2 and a total absolute B mag of ∼-10. In this paper we carry out an analysis of their morphology, (B-I) colours and atomic hydrogen content. We compare these properties with those of dwarf galaxies in other environments to try and assess how the cluster environment has influenced their evolution. Field dwarfs are generally of a more irregular morphology , are bluer and contain relatively more gas. We assess the importance that various physical processes have on the evolution of cluster dwarf galaxies (ram pressure stripping , tidal interactions, supernova driven gas loss). We suggest that enhanced star formation triggered by tidal interactions is the major reason for the very different general properties of cluster dwarfs: they have undergone accelerated evolution.

We have carried out a fully sampled large area (4°× 8°) 21‐cm H i line survey of part of the Virgo cluster using the Jodrell Bank multibeam instrument. The survey has a sensitivity some three times better than the standard HIJASS (H i Jodrell All Sky Survey) and HIPASS (H i Parkes All Sky Survey) surveys. We detect 31 galaxies, 27 of which are well‐known cluster members. The four new detections have been confirmed in the HIPASS data and by follow‐up Jodrell Bank pointed observations. One object lies behind M86, but the other three have no obvious optical counterparts upon inspection of the digital sky survey fields. These three objects were mapped at Arecibo with a smaller 3.6‐arcmin half power beam width (HPBW) and a four times better sensitivity than the Jodrell Bank data, which allow an improved determination of the dimensions and location of two of the objects, but surprisingly failed to detect the third. The two objects are resolved by the Arecibo beam, giving them a size far larger than any optical images in the nearby field. To our mass limit of 5 × 107(Δv/50 km s−1) M⊙ and column density limit of 3 × 1018(Δv/50 km s−1) atom cm−2, these new detections represent only about 2 per cent of the cluster atomic hydrogen mass. Our observations indicate that the H i mass function of the cluster turns down at the low‐mass end, making it very different to the field galaxy H i mass function. This is quite different to the Virgo cluster optical luminosity function, which is much steeper than that in the general field. Many of the sample galaxies are relatively gas‐poor compared with H i selected samples of field galaxies, confirming the ‘anaemic spirals’ view of Virgo cluster late‐type galaxies. The velocity distribution of the H i detected galaxies is also very different to that of the cluster as a whole. There are relatively more high‐velocity galaxies in the H i sample, suggesting that they form part of a currently infalling population. The H i sample with optical identifications has a minimum H i column density cut‐off more than an order of magnitude above that expected from the sensitivity of the survey. This observed column density is above the normally expected level for star formation to occur. The two detections with no optical counterparts have very much lower column densities than that of the rest of the sample, below the star formation threshold.