Found 24 talks width keyword galactic kinematics

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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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Wednesday July 16, 2008
Netherlands Institute for Radio Astronomy, the Netherlands

Abstract

Warps of disk galaxies are ubiquitous. In almost every disk galaxy a bending of the disk occurs where the stars fade away and hence where the dark matter halo becomes dominant. A clear understanding of this phenomenon has not been reached yet. Analysing H I observations of a small sample of symmetric, warped disk galaxies we found that they exhibit a two-disk structure, the warp being the transition from the inner flat disk to an outer, inclined one. At the transition radius, the rotation curve changes. This points towards symmetric warps being a long-lived phenomenon reflecting an internal change in the structure of the Dark Matter halo.
While warps usually occur where the stellar disks fade, examples of extreme warps are known that commence already at the centre of galaxies. One is present in the neutral gas disk of the "Spindle Galaxy "NGC 2685, formerly thought of as being a two-ringed polar ring galaxy. Utilising deep HI observations, we found that the two-ringed appearance is due to projection effects and that it rather possesses one coherent,extremely warped HI disk. Our success in fitting a tilted-ring model to the HI component, and, with that, assuming circular orbits of the tracer material, and the shape of the fitted rotation curve hint towards a rather spherical shape of the overall potential.

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Thursday May 22, 2008
Instituto de Estructura de la Materia, CSIC, Spain
University of Sheffield, UK

Abstract

1) In this brief seminar (<~25 minutes+questions) I will present recent results on the study of "deep", high resolution, surface brightness profiles of a sample of ~500 late-type galaxies in the redshift range 0.1—1.1, making use of publicly available HST/ACS imaging of the GOODS-South field. We have classified and parameterized, according to usual prescriptions in this kind of analysis, these profiles, with special emphasis put on the so called ``truncated'' disks. This is the case in which, beyond a certain radius, termed as ``Break Radius'', the exponentially decaying surface brightness profile along the stellar disk gives way to an even more abrupt exponential decay. This radius can be taken as an spatial "scale" for the disk, as observed in a given band (in our case, the rest-frame B-band). Comparing with analogous analysis for galaxies in the Local Universe, as we have done, it is possible to extract valuable information on the evolution of several photometric properties of the stellar disks of galaxies, related to the stellar populations distributions. I will also present results on the analysis of the color profiles of this sample of galaxies, which have yield an interesting result which is, perhaps, the main reason that justifies calling this talk a "breaking news" seminar, as I will show. Summarizing, an overview of the results we have obtained will be given, and our conclusions on them, explaining how they can be understood in the frame of Galaxy Evolution (2) Based on high quality near-infrared spectroscopy (obtained with WHT/LIRIS) we reveal that the nucleus of Mrk 573 is an obscured Narrow-Line Seyfert 1 and not an archetypal Seyfert 2 as it has been classified until now. Currently only four AGNs have been classified into this category. We have detected permitted OI and FeII transitions, which indicates the existence of a high density region similar to the BLRs detected in type 1 AGN.


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