Found 21 talks width keyword galactic kinematics
AbstractTwo-dimensional stellar kinematics obtained with the integral-field spectrograph SAURON allow the classification of early-type galaxies into 'slow' and 'fast' rotators, different from their morphological classification into ellipticals and lenticulars. Most fast rotators, including lenticular as well as many elliptical galaxies, are consistent with oblate axisymmetric disk-like systems. On the other hand, the slow-rotator ellipticals show clear deviations from axisymmetry, which can be modeled with our extension of Schwarzschild's orbit superposition method to triaxial geometry. Besides galaxies, I show that Schwarzschild's method can also be used to model in detail globular clusters such as ω Cen and M15. The recovered internal orbital structure of ω Cen reveals besides a signature of tidal interaction, also a central stellar disk, supporting its origin as the nucleus of a stripped dwarf galaxy. The formally best-fit Schwarzschild model for M15 includes an intermediate-mass black hole, but we cannot exclude a model in which dark remnants make up the dark mass in the collapsed core.
AbstractWhen we measure the electron density within an H II region using ratios of emission lines we find characteristic values in the range of 100-300 cm-3. But when we make these measurements using the total luminosity in Hα and the overall radial size of an H II region we find average values in the range 3-10. I will first explain how this discrepancy occurs, and then go on to show some measurements of electron densities in the H II regions of M51 (over 2500 regions) and the dwarf galaxy NGC 4449 (over 250 regions) using the second method, by Leonel Gutiérrez and myself. From these measurements we can infer how the electron density varies with the radial size of an individual region, and how it varies as we move from the center of the galaxy disc to the outside. Some interesting simple global relationships are found, which tell us about the interaction of star forming regions with their surroundings and how this interaction varies across the face of a galaxy.
AbstractΛCDM-based numerical simulations predict a scenario consistent with observational evidence in Milky Way-like halos. However, less clear is the role of low-mass galaxies in the big picture. The best way to answer this question is to study the nearest example of a dwarf spiral galaxy, M33. We will use star clusters to understand the structure, kinematics and stellar populations of this galaxy. We will present our current status and future plans of a comprehensive study of the star cluster system of M33. This study will provide key insights into the star formation history, composition and kinematics of low-mass galaxies as well as place M33 within the context of galaxy formation process.
AbstractThe SAURON survey has revised our view of early type galaxies discovering that central disks and multiple kinematic components are common; 75% of the sample have extended ionized gas, often misaligned with the stars; half of S0s and 25% of Es have intermediate age populations. There is a tight relationship between the escape velocity and Mg line strength which holds both within and between galaxies raising uncomfortable questions for hierarchical assembly. Many of the properties of ETGs are related to a measure of their specific angular momentum : slow rotators are triaxial, close to spherical, isotropic and frequently exhibit decoupled central kinematics, whereas fast rotators are intrinsically flatter, oblate, have disk-like (anisotropic) kinematics and often have Mg enhanced disks. In general the slow rotators are more massive and have older populations Only half of the elliptical galaxies exhibit slow rotation, the remainder have stellar disks showing that the historic division by morphological class is physically misleading. We suggest that the contrasting physical properties of fast and slow rotators arise through distinct assembly histories with slow rotators forming in gas free, dry mergers and fast rotators retaining a disk component through a dissipative merger.
AbstractObservations have shown that massive galaxies at high redshift have much smaller sizes than galaxies of similar mass today. The mean stellar density of such objects was almost two orders of magnitude higher than the ones we measured in the most massive nearby galaxies, reaching, in some cases, densities similar to those observed in globular clusters. What is the nature of these objects? And, how these objects have been transformed into the present population of massive galaxies? We will summarize the recent findings our group has done on this topic. In particular, we will focus on our search for finding relics of these compact galaxies in the nearby universe, and the effort we have done for measuring the evolution of the velocity dispersion of these galaxies in the last 10 Gyr. The implications of this research within the galaxy formation scenario will be discussed.
AbstractFrom galaxy formation theory we expect galaxies to be embedded in massive dark matter haloes. For spiral and dwarf galaxies this has indeed been observationally confirmed, by modeling the kinematics from the large cold gas discs that often surround these galaxies. These gas discs are however rare in elliptical galaxies, so that we have to resort to other tracers when we want to probe their dark matter haloes, which are not always easily accessible. As a result, dark haloes for only a handful of early-type galaxies have been mapped. In this talk I will give an overview of the methods that can be used to find dark matter in early-type galaxies. I will then focus on two projects that I worked on with the integral-field spectrograph SAURON, using two different methods to constrain the dark halo. The first is based on the combination of two-dimensional ionised gas and cold gas kinematics. The second method uses SAURON as a 'photon collector', to obtain spectra at large radii in galaxies. From these spectra we can not only obtain the velocity profile and construct mass models to constrain the dark halo, but also infer the properties of the stellar halo population. I will show the results from these two projects and discuss some future prospects.
AbstractPeculiar velocities of galaxies, derived using distance estimators, are plagued with systematic effects and are unreliable beyond 100 Mpc/h. In Kashlinsky & Atrio-Barandela (2000) we proposed to measure peculiar velocities of clusters of galaxies using the temperature anisotropies on the Cosmic Microwave Background generated by the hot X-ray emitting. Using this technique we have recently found a bulk flow velocity of amplitude 600-1000 km/s in the same direction as the CMB dipole and encompassing a sphere of 300 Mpc/h radius. We shall discuss the cosmological implications of this measurement.
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.
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.
AbstractWarps 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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