Search

The stellar disc kinematics in a sample of fifteen intermediate- to late-type edge-on spiral galaxies are studied using a dynamical modeling 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. Dynamical models of the stellar discs are constructed using the disc structure from $I$-band surface photometry and rotation curves observed in the gas. The differences in the line-of-sight stellar kinematics between the models and absorption line spectroscopy are minimized using a least-squares approach. The modeling constrains the disc surface density and stellar radial velocity dispersion at a fiducial radius through the free parameter $\sqrt{M/L}$ $(\sigma_{\rm z}/\sigma_{\rm R})^{-1}$, where $\sigma_{\rm z}/\sigma_{\rm R}$ is the ratio of vertical and radial velocity dispersion and $M/L$ the disc mass-to-light ratio. For thirteen spirals a transparent model provides a good match to the mean line-of-sight stellar velocity dispersion. Models that include a realistic radiative transfer prescription confirm that the effect of dust on the observable stellar kinematics is small at the observed slit positions. We discuss possible sources of systematic error and conclude that most of these are likely to be small. The exception is the neglect of the dark halo gravity, which has probably caused an overestimate of the surface density in the case of low surface brightness discs., Comment: Accepted for publication by the Monthly Notices of the R.A.S

In earlier papers in this series we determined the intrinsic stellar disc kinematics of fifteen intermediate to late type edge-on spiral galaxies using a dynamical modeling technique. From the photometry we find that intrinsically more flattened discs tend to have a lower face-on central surface brightness and a larger dynamica 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 modeling that at least twelve discs are submaximal. The average disc contributes 53$\pm$4 percent to the observed rotation at 2.2 disc scalelengths, with a 1$\sigma$ scatter of 15 percent. 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$h_{\rm R}$ the submaximal nature of discs is independent of barredness. The possibility remains that very high surface brightness discs are maximal.We confirm that the radial stellar disc velocity dispersion is related to the galaxy maximum rotational velocity. The scatter in this $\sigma-v_{\rm max}$ 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., Comment: Accepted for publication by Mon. Not. R.A.S

We discuss the possible origin of the radial truncations in stellar discs, using measurements that we presented in an earlier paper (Kregel, van der Kruit & de Grijs, 2002). A tentative correlation is found with the de-projected face-on central surface brightness; lower surface brightness discs tend to have a smaller truncation radius in units of scalelength. This and our earlier finding that in smaller spirals the truncation tends to occur at a larger number of scalelengths are best reproduced when the truncation is caused by a constant gas density threshhold on star formation., Accepted for publication by Mon. Not. R.A.S

We present deep optical long-slit spectra of 17 edge-on spiral galaxies of intermediate to late morphological type, mostly parallel to their major axes and in a few cases parallel to the minor axes.The line-of-sight stellar kinematics are obtained from the stellar absorption lines using the improvedc ross-correlation technique. In general, the stellar kinematics are regular and can be traced well into the disc-dominated region. The mean stellar velocity curves are far from solid-body, indicating that the effect of dust extinction is not large. The line-of-sight stellar disc velocity dispersion correlates with the galaxy maximum rotational velocity, but detailed modeling is necessary to establish whether this represents a physical relation. In four spirals with a boxy- or peanut-shaped bulge we are able to detect asymmetric velocity distributions, having a common signature with projected radius in the mean line-of-sight velocity and the $h_{3}$ and $h_{4}$ curves. In two cases this kinematic asymmetry probably represents the `figure-of-eight' pattern synonymous of a barred potential. We emphasize, however, that the signatures seen in the $h_{3}$ and $h_{4}$ curves may also be due to the disc seen in projection., Comment: Accepted for publication by Mon. Not. R.A.S

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 microns 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 NGC4945. 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 NGC4945 to ongoing massive star formation. Our M-band spectrum also shows strong HI Pfund-beta and H2 0-0 S(9) line emission and gas phase CO absorption lines. The HI, H2, 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:IRS19. 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 NGC4945 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., 9 pages, 8 figures. Accepted for publication in A&A. Also available at this http://www.astro.rug.nl/~spoon/publications.html

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., 25 pages, 7 figures, appendix, Accepted for MNRAS (April 4 2002)

We present spectroscopic observations of the stellar motions in the disk of the superthin edge-on spiral galaxy IC 5249 and re-analyse synthesis observations of the HI. We find that the HI rotation curve rises initially to about 90-100 km/s, but contrary to the conclusion of Abe et al. (1999) flattens well before the edge of the optical disk. Over most part of the optical disk we have been able to establish that the (tangential) stellar velocity dispersion is 25-30 km/s. From earlier surface photometry we adopt a value for the radial scalelength of the disk of 7 +/- 1 kpc, a vertical scaleheight of 0.65 +/- 0.05 kpc and a disk truncation radius of 17 +/- 1 kpc. The very thin appearance of IC 5249 on the sky is the result of a combination of a low (face-on) surface brightness, a long scalelength and a a sharp truncation at only about 2.5 scalelengths. From various arguments we derive the stellar velocity dispersions at a position one radial scalelength as sigma_R about 35 km/s, sigma_{theta} about 30 km/s and sigma_z about 20 km/s. This is comparable to the values for the disk of our Galaxy in the solar neighborhood., Comment: 11 pages and 8 figures. Accepted for Astronomy and Astrophysics (September 2001)

We present Australia Telescope Compact Array (ATCA) and Westerbork Synthesis Radio Telescope (WSRT) HI observations of 15 edge-on spiral galaxies of intermediate to late morphological type. The global properties and the distribution and kinematics of the HI gas are analysed and discussed. We determine the rotation curves using the envelope-tracing method. For 10 spiral galaxies with a stellar disc truncation we find an average ratio of the HI radius to the truncation radius of the stellar disc of 1.1 +/- 0.2 (1 sigma). This paper has been accepted by MNRAS and is available in pdf-format at the following URL: http://www.astro.rug.nl/$\sim $vdkruit/jea3/homepage/paperII.pdf, Comment: Accepted for oublication in MNRAS

The HI 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 HI 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), suggesting that the disk is highly perturbed as already indicated by optical emission line spectroscopy. There are, in addition, two prominent HI tails, one extending to the north-west and the other, somewhat patchy, to the south. These HI 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., 10 pages, 11 figures, accepted for publication in A&A

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., 11 pages LaTeX, incl. 7 postscript figures, MNRAS, accepted; major revisions included