Flattening and truncation of stellar discs in edge-on spiral galaxies

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

Radially truncated galactic discs

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

Structure and kinematics of edge-on galaxy disks

TIJDENS het aanschouwen van de pracht van de sterrenhemel bekruipt menigeen een gevoel van verwondering en nietigheid, waarna al gauw vragen rijzen omtrent haar oorsprong, samenstelling en toekomst. In de voorgaande eeuw zijn, dankzij de versnelde samenloop van wetenschappelijke ontdekkingen en technologische ontwikkelingen, veel van deze vragen beantwoord. Zo is een enorme vooruitgang geboekt naar een alomvattend beeld van ons universum. De talloze sterren die ’s nachts met het blote oog zichtbaar zijn blijken slechts tot de meest nabije omgeving van onze zon te horen. Met haar omringende planeten en haar leeftijd van vier en een half miljard jaar is onze zon een gemiddelde ster, ´e´en van de ruwweg 100 miljard sterren die onze Melkweg rijk is. ... Zie: Samenvatting