Found 13 talks width keyword spiral galaxies

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Tuesday March 24, 2009
Laboratoire d'Astrophysique de Marseille, France

Abstract

I will propose a new theory to explain the formation and properties of rings and spirals in barred galaxies, focusing on a comparison of theoretical results to observations and giving some predictions for further comparisons. This theory can account for both spirals and rings, the latter both inner and outer. The model outer rings have the observed R1, R_1', R_2, R_2' and R_1R_2 morphologies, including the dimples near the direction of the bar major axis. It explains why the vast majority of spirals in barred galaxies are two armed and trailing and I will discuss what it takes for higher multiplicity arms to form. The shapes of observed and theoretical spirals agree and the theory predicts that stronger non-axisymmetric forcings at and somewhat beyond corotation will drive more open spirals. I will compare the ratio of ring diameters in theory and in observations and predict that more elliptical rings will correspond to stronger forcings. This theory also provides the right building blocks for the rectangular-like bar outline and for ansae.


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Thursday December 18, 2008
University of Nottingham, UK

Abstract

We present a detailed study of the lenticular galaxy NGC 1023 kinematics. To perform this analysis we use planetary nebulae (PNe). which can be observed in the faint outer regions of the galaxy, where traces of the galaxy past history are clearly recorded. If the circular speed is equal or lower than the stars velocity dispersion, the system is hot and it is the result of a minor merger. Otherwise, if the stellar motions are rotation dominated at large radii, a spiral galaxy is the progenitor of the lenticular. A first attempt at such an analysis was undertaken by Noordermeer et al. (2008), who found that the S0 system NGC 1023 has very peculiar kinematics in its disk, which do not seem to be consistent with either of the above scenarios. In this paper we show that that result was largely due to a contamination of the disk kinematics by stars belonging to the spheroidal component or accreted from the small companion. We present a new method based on a more sophisticated maximum-likelihood analysis that uses a full two-dimensional disk/spheroid decomposition to solve simultaneously for both disk and spheroid kinematics. This analysis reveal that NGC1023 has the kinematics expected for a stripped spiral galaxy.


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Friday October 24, 2008
Instituto de Astrofísica de Canarias, Spain

Abstract

(1) We present SAURON integral-field stellar velocity and velocity dispersion maps for four double-barred early-type galaxies: NGC2859, NGC3941,NGC4725 and NGC5850. The presence of the nuclear bar is not evident from the radial velocity, but it appears to have an important effect in the stellar velocity dispersion maps: we find two sigma-hollows of amplitudes between 10 and 40 km/s at either sides of the center, at the ends of the nuclear bars. We have performed numerical simulations to explain these features. Ruling out other possibilities, we finally conclude that, although the sigma-hollows may be originated by a younger stellar population component with low velocity dispersion, more likely they are an effect of the contrast between two kinematically different components: the high velocity dispersion of the bulge and the ordered motion (low velocity dispersion) of the nuclear bar.

(2) We have explored radial color and stellar surface mass density profiles for a sample of 85 late-type galaxies with available deep (down to ~27.0 mag/arcsec2 SDSS g'- and r'-band surface brightness profiles. About 90% of the light profiles have been classified as broken exponentials, exhibiting either truncations (Type II galaxies) or antitruncations (Type III galaxies). Their associated color profiles show significantly different behavior. For the truncated galaxies a radial inside-out bluing reaches a minimum of (g' - r') = 0.47 +/- 0.02 mag at the position of the break radius, this is followed by a reddening outwards. The anti-truncated galaxies reveal a more complex behavior: at the break position (calculated from the light profiles) the color profile reaches a plateau region - preceded with a reddening - with a mean color of about (g' - r') = 0.57 +/- 0.02 mag. Using the color to calculate the stellar surface mass density profiles reveals a surprising result. The breaks, well established in the light profiles of the Type II galaxies, are almost gone, and the mass profiles resemble now those of the pure exponential Type I galaxies. This result suggests that the origin of the break in Type II galaxies are most likely to be a radial change in stellar population, rather than being caused by an actual drop in the distribution of mass. The anti-truncated galaxies on the other hand preserve their shape to some extent in the stellar surface mass density profiles. We find that the stellar surface mass density at the break for truncated (Type II) galaxies is 13.6 +/- 1.6 Msun/pc2 and 9.9 +/- 1.3 Msun/pc2 for the anti-truncated (Type III) ones. We estimate that ~15% of the total stellar mass in case of Type II galaxies and ~9% in case of Type III galaxies are to be found beyond the measured break radii.

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