On the 3 dimensional structure of edge-on disk galaxies

A simple algorithm is employed to deproject the two dimensional images of a pilot sample of 12 high-quality images of edge-on disk galaxies and to study their intrinsic 3 dimensional stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dustlane. This could be explained by the widespread presence of a thick disk component in these galaxies. In addition, the 3 dimensional view allows the study of the vertical distribution of the outer disk, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated disks. This could be regarded as a weakening of the "truncation" with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies.Comment: LaTeX, 25 pages, 10 figures (some low resolution), MNRAS accepted. Version with all figures in full resolution (~6MB) available at http://www.astro.rug.nl/~pohlen/pohlen_3Dedgeon.p

Trends for Outer Disk Profiles

The surface-brightness profiles of galaxy disks fall into three main classes, based on whether they are simple exponentials (Type I), bend down at large radii (Type II, "truncations") or bend up at large radii (Type III, "antitruncations"). Here, we discuss how the frequency of these different profiles depends on Hubble type, environment, and the presence or absence of bars; these trends may herald important new tests for disk formation models.Comment: LaTeX, 2 pages, 1 EPS figure, uses modified newpasp.sty (included). To appear in Formation and Evlution of Galaxy Disks, eds. J.G. Funes and E.M. Corsin

Three-dimensional modelling of edge-on disk galaxies

We present detailed three-dimensional modelling of the stellar luminosity distribution for the disks of 31 relatively nearby (<= 110 Mpc) edge-on spiral galaxies. In contrast to most of the standard methods available in the literature we take into account the full three-dimensional information of the disk. We minimize the difference between the observed 2D-image and an image of our 3D-disk model integrated along the line of sight. Thereby we specify the inclination, the fitting function for the z-distribution of the disk, and the best values for the structural parameters such as scalelength, scaleheight, central surface brightness, and a disk cut-off radius. From a comparison of two independently developed methods we conclude, that the discrepancies e.g. for the scaleheights and scalelengths are of the order of ~10%. These differences are not due to the individual method itself, but rather to the selected fitting region, which masks the bulge component, the dust lane, or present foreground stars. Other serious limitations are small but appreciable intrinsic deviations of real disks compared to the simple input model. In this paper we describe the methods and present contour plots as well as radial profiles for all galaxies without previously published surface photometry. Resulting parameters are given for the complete sample.Comment: LaTeX, 25 pages, 28 figures higher quality figures available at http://www.astro.ruhr-uni-bochum.de/astro/publications/pub2000.htm

Outer edges of face-on spiral galaxies

We present deep optical imaging of three face-on disk galaxies together with a detailed description of the reduction and calibration methods used, in order to measure the intrinsic shape of their outer stellar edges. Whereas it is now well accepted that disks of spiral galaxies are not infinite exponential beyond galactocentric distances of about 3-5 radial scalelengths, the genuine structure of the truncation region is not yet well known. Our data quantitatively establish a smooth truncation behaviour of the radial surface brightness profiles and is best described by a two-slope model, characterised by an inner and outer exponential scalelength separated at a relatively well defined break radius. This result disagrees with the frequently assumed sharply truncated nature of the radial surface brightness profiles and implies the presence of stars and even star-formation beyond the break radius. In addition, we do not find a strong influence of a nearby companion on the ratio of the break radius to the radial scalelength. Our results denote new observational constraints for the search of the physical explanation for these smooth disk truncations.Comment: LaTeX, 10 pages, 17 figures, accepted to be published in A&A, minor changes to the quality of figure

Land landing couch dynamics computer program

Computer programs perform landing stability studies of mechanical impact system designs for advanced spacecraft. The programs consider variation in spacecraft vertical and horizontal velocity, attitude and orientation, shock strut load-stroke characteristics, and ground coefficient of friction

A framework for evaluating supply chain performance

Managers require measures spanning multiple enterprises to increase supply chain competitiveness and to increase the value delivered to the end-customer. Despite the need for supply chain metrics, there is little evidence that any firms are successfully measuring and evaluating interfirm performance. Existing measures continue to capture intrafirm performance and focus on traditional measures. The lack of a framework to simultaneously measure and translate interfirm performance into value creation has largely contributed to this situation. This article presents a framework that overcomes these shortcomings by measuring performance across multiple firms and translating supply chain performance into shareholder value

Anti-truncated stellar light profiles in the outer regions of STAGES spiral galaxies: bulge or disc related?

We present a comparison of azimuthally averaged radial surface brightness mu(r) profiles and analytical bulge-disc decompositions (de Vaucouleurs, r^(1/4) bulge plus exponential disc) for spiral galaxies using Hubble Space Telescope/Advanced Camera for Surveys V-band imaging from the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). In the established classification scheme, antitruncated mu(r) profiles (Type III) have a broken exponential disc with a shallower region beyond the break radius r_brk. The excess light at large radii (r > r_brk) can either be caused by an outer exponential disc (Type III-d) or an extended spheroidal component (Type III-s). Using our comparisons, we determine the contribution of bulge light at r > r_brk for a large sample of 78 (barred/unbarred, Sa-Sd) spiral galaxies with outer disc antitruncations (mu_brk > 24 mag arcsec^-2). In the majority of cases (~85 per cent), evidence indicates that excess light at r > r_brk is related to an outer shallow disc (Type III-d). Here, the contribution of bulge light at r > r_brk is either negligible (~70 per cent) or too little to explain the antitruncation (~15 per cent). However in the latter cases, bulge light can affect the measured disc properties (e.g. mu_brk, outer scalelength). In the remaining cases (~15 per cent), light at r > r_brk is dominated by the bulge (Type III-s). Here, for most cases the bulge profile dominates at all radii and only occasionally (3 galaxies, ~5 per cent) extends beyond that of a dominant disc and explains the excess light at r > r_brk. We thus conclude that in the vast majority of cases antitruncated outer discs cannot be explained by bulge light and thus remain a pure disc phenomenon.Comment: Accepted to MNRA

The Outer Structure of Galactic Disks: Connections Between Bars, Disks, and Environments

Surface-brightness profiles for early-type (S0-Sb) disks exhibit three main classes (Type I, II, and III). Type II profiles are more common in barred galaxies, and most of the time appear to be related to the bar's Outer Lindblad Resonance. Roughly half of barred galaxies in the field have Type II profiles, but almost none in the Virgo Cluster do; this might be related to ram-pressure stripping in clusters. A strong \textit{anti}correlation is found between Type III profiles ("antitruncations") and bars: Type III profiles are most common when there is no bar, and least common when there is a strong bar.Comment: LaTeX, 4 pages, 2 EPS figures, uses modified newpasp.sty (included). To appear in Pathways through an Eclectic Universe, eds. J. H. Knapen, T. J. Mahoney, & A. Vazdeki

The puzzle about the radial cut-off in galactic disks

The stellar disk in a spiral galaxy is believed to be truncated physically because the disk surface brightness is observed to fall faster than that for an exponential in the outer, faint regions. We review the literature associated with this phenomenon and find that a number of recent observations contradict the truncation picture. Hence we question the very existence of a physical outer cut-off in stellar disks. We show, in this paper, that the observed drop in the surface brightness profiles in fact corresponds to a negligible decrease in intensity, and that this minor change at the faint end appears to be exaggerated on a log-normal plot. Since minor deviations from a perfect exponential are common throughout the disk, we suggest that such a deviation at the faint end could easily give rise to the observed sharp drop.Comment: 4 pages, 3 .eps figures, Astron. & Astrophys Letters, In pres