We analyse the global structure of the old stellar discs in 34 edge-on spiral galaxies. The radial and vertical exponential scale parameters of the discs are obtained by applying an improved two-dimensional decomposition technique to our I-band photometry. We find a clear increase in the disc scaleheight with maximum rotational velocity, in accordance with observations of the stellar velocity dispersions in galaxy discs. The range and maximum of the intrinsic flattening of the disc light seem to increase with both maximum rotational velocity and total HI mass. We use the disc flattening to estimate the disc contribution to the maximum rotational velocity, resulting in an average of 57+-22 percent. The disc light distributions are further investigated for the presence of radial truncations. We find that the radial light distributions of at least 20 spirals are truncated, corresponding to 60 percent of the sample. For small scalelength spirals, which are the most numerous in the local Universe, the results suggest that the average ratio of disc truncation radius to disc scalelength is at least four.Comment: 25 pages, 7 figures, appendix, Accepted for MNRAS (April 4 2002

In earlier papers in this series we determined the intrinsic stellar disc kinematics of 15 intermediate‐ to late‐type edge‐on spiral galaxies using a dynamical modelling technique. The sample covers a substantial range in maximum rotation velocity and deprojected face‐on surface brightness, and contains seven spirals with either a boxy or peanut‐shaped bulge. Here we discuss the structural, kinematical and dynamical properties. From the photometry we find that intrinsically more flattened discs tend to have a lower face‐on central surface brightness and a larger dynamical mass‐to‐light ratio. This observation suggests that, at a constant maximum rotational velocity, lower surface brightness discs have smaller vertical stellar velocity dispersions. Although the individual uncertainties are large, we find from the dynamical modelling that at least 12 discs are submaximal. The average disc contributes 53 ± 4 per cent to the observed rotation at 2.2 disc scalelengths (hR), with a 1σ scatter of 15 per cent. This percentage becomes somewhat lower when effects of finite disc flattening and gravity by the dark halo and the gas are taken into account. Since boxy and peanut‐shaped bulges are probably associated with bars, the result suggests that at 2.2 hR the submaximal nature of discs is independent of barredness. The possibility remains that very high surface brightness discs are maximal, as these discs are underrepresented in our sample. We confirm that the radial stellar disc velocity dispersion is related to the galaxy maximum rotational velocity. The scatter in this σ versus vmax relation appears to correlate with the disc flattening, face‐on central surface brightness and dynamical mass‐to‐light ratio. Low surface brightness discs tend to be more flattened and have smaller stellar velocity dispersions. The findings are consistent with the observed correlation between disc flattening and dynamical mass‐to‐light ratio and can generally be reproduced by the simple collapse theory for disc galaxy formation. Finally, the disc mass Tully–Fisher relation is offset from the maximum‐disc scaled stellar mass Tully–Fisher relation of the Ursa Major cluster. This offset, −0.3 dex in mass, is naturally explained if the discs of the Ursa Major cluster spirals are submaximal.

We present the first results of a systematic analysis of radially truncated exponential discs for four galaxies of a complete sample of disc-dominated edge-on spiral galaxies. The discs of our sample galaxies are truncated at similar radii on either side of their centres. With possible the exception of the disc of ESO 416-G25, it appears that the truncations in our sample galaxies are closely symmetric, in terms of both their sharpness and the truncation length. However, the truncations occur over a larger region and not as abruptly as found in previous studies. We show that the truncated luminosity distributions of our sample galaxies, if also present in the mass distributions, comfortably meet the requirements for longevity. The formation and maintenance of disc truncations are likely closely related to stability requirements for galactic discs.Comment: 11 pages LaTeX, incl. 7 postscript figures, MNRAS, accepted; major revisions include

Abstract. The composition of ice grains provides an important tool for the study of the molecular environment of star forming regions. Using ISAAC at the VLT to obtain spectra around 4.65 µm we have detected for the first time "XCN" and CO ice in an extragalactic environment: the nuclear region of the nearby dusty starburst/AGN galaxy NGC 4945. The profile of the solid CO band reveals the importance of thermal processing of the ice while the prominence of the XCN band attests to the importance of energetic processing of the ice by FUV radiation and/or energetic particles. In analogy to the processing of ices by embedded protostars in our Galaxy, we attribute the processing of the ices in the center of NGC 4945 to ongoing massive star formation. Our M-band spectrum also shows strong HI Pfβ and H 2 0-0 S(9) line emission and gas phase CO absorption lines. The HI, H 2 , PAH, gas phase CO and the ices seem to be embedded in a rotating molecular disk which is undergoing vigorous star formation. Recently, strong OCN − absorption has been detected in the spectrum of the Galactic center star GC: IRS 19. The most likely environment for the OCN − absorption is the strongly UV-exposed GC molecular ring. The presence of processed ice in the center of NGC 4945 and our Galactic center leads us to believe that processed ice may be a common characteristic of dense molecular material in star forming galactic nuclei.

Abstract. The H i structure and kinematics of the peculiar starburst galaxy NGC 3310 (Arp 217, UGC 5786) are discussed. New evidence bearing on the origin of the starburst is presented. The bulk of H i coincides with the bright optical disk and shows differential rotation. Its velocity dispersion is, however, unusually large for a spiral galaxy (up to 40 km s −1 ), suggesting that the disk is highly perturbed as already indicated by optical emission line spectroscopy. There are, in addition, two prominent H i tails, one extending to the north-west and the other, somewhat patchy, to the south. These H i tails, the perturbed kinematics and the peculiar optical morphology strongly suggest a recent merger between two gas-rich galaxies. This seems to have been a major merger in which most of the gas in the inner parts has been preserved in neutral atomic form and either one of the progenitor disks has survived or a new disk has formed.