Galaxy dynamics

Both pieces of evidence concern spiral galaxies the first concerns the nature of the cosmological redshift measured for such objects, while the second concerns the nature of spiral galaxy dynamics. To have a clear appreciation of the issues, some background knowledge is useful. 

Observations of galaxy duster do not help in this respect since the available data stop our understanding of the DM density profile at distances r 10 kpc from their centres (see Fig.5.1). Down to these scales the NFW is still allowed and at smaller scales the inner slope remains quite uncertain even when the combined analysis of X-ray, gravitational lensing and galaxy dynamics data are taken into account (Dalai Keeton 2003). 

The scarcity of data and their invaluable content require that they be recorded in the most careful manner. The human eye is an incredibly powerful and versatile instrument, with an amazing dynamic range. But almost the entire universe is beyond its reach. Modem telescopes have a sensitivity 9 to 10 order of magnitude higher, yet they are barely able to provide a glimpse at the youngest galaxies, least to say stars. 

Abstract. In an effort to determine accurate stellar parameters and abundances for a large sample of nearby stars, we have performed the detailed analysis of 350 high-resolution spectra of FGK dwarfs and giants. This sample will be used to investigate behavior of chemical elements and kinematics in the thick and thin disks, in order to better constrain models of chemical and dynamical evolution of the Galaxy. 

Scl is a close companion of the Milky Way, at a distance of 72 5 kpc [7], with a low total (dynamical) mass, (1.4 0.6) x 107Mq [8], and modest luminosity, My = —10.7 0.5, and central surface brightness, Soy = 23.5 0.5 mag/arcsec2 [9] with no HI gas [10]. CMD analysis, including the oldest Main Sequence turnoffs, has determined that this galaxy is predominantly old and that the entire star formation history can have lasted only a few Gyr [11]. 

Typical timescales 1/v range from as little as 108 years (roughly the dynamical timescale) for a starburst galaxy to maybe 2 x 109 years in an early-type spiral to... 

Thus the mass of stars and that of the whole system steadily increase while z soon approaches 1 and the stellar metallicity distribution is very narrow (see Fig. 8.24). The accretion rate is constant in time if the star formation rate is any fixed function of the mass of gas. Other models in which the accretion rate is constant, but less than in the extreme model, have been quite often considered in the older literature (e.g. Twarog 1980), but are less popular now because they are not well motivated from a dynamical point of view, there is an upper limit to the present inflow rate into the whole Galaxy of about 1 M0yr 1 from X-ray data (Cox Smith 1976) and they do not provide a very good fit to the observed metallicity distribution function. 

Numerical modelling of the chemical evolution of the Milky Way and/or similar disk galaxies, taking into account dynamical effects, was pioneered by Larson (1976) and Tinsley and Larson (1978). Because of many uncertainties in the details... 

Fig. 8.37. The different gaseous and stellar components connected via mass, momentum and energy exchange, with their principal interactions, in the chemo-dynamical model of the Galaxy, after Samland, Hensler and Theis (1997). Courtesy Gerhard Hensler.

Parameters of dynamically hot galaxies , i.e. various classes of ellipticals and the bulges of spirals, generally lie close to a Fundamental Plane in the 3-dimensional space of central velocity dispersion, effective surface brightness and effective radius or equivalent parameter combinations (Fig. 11.10). This is explained by a combination of three factors the Virial Theorem, some approximation to... 

Fig. 11.11. Relation between central Mg2 index and central velocity dispersion for dynamically hot galaxies. Coding as in Fig. 11.10. Adapted from Bender (1992).

O.J. Eggen, D. Lynden-Bell and Sandage assemble dynamical and chemical evidence for formation of the Galaxy by free-fall collapse. The issue is still debated. 

Freeman, K. C. 1990, in R. Wielen (ed.), Dynamics and Interactions of Galaxies, Berlin Springer-Verlag, p. 36. 

Renzini, A., Ciotti, L. Pellegrini, S. 1993, in I. J. Danziger, W. W. Zeilinger K.Kjar (eds.), ESO Conference Workshop Proc. no. 45 Structure, Dynamics and Chemical Evolution of Elliptical Galaxies, Garching ESO, p. 443. 

As is well known, the expansion of the Universe was revealed through the redshifting of light from distant galaxies. The fate of such a dynamic universe then became one of the main questions to be addressed by cosmology. 

Summing up the dynamical argument, telescopes reveal the architecture and motions of the cosmos on every scale. Planets, stars, galaxies, and clusters of galaxies are nested one within the other like Chinese boxes. But then the need for dark matter suddenly arises. Without it, stars at the edge of our Galaxy would fly off and the swarms of galaxies in clusters would scatter like birds. 

The rotation curve is calculated in two steps (1) by subtracting the global redshift component (i.e., cosmological redshift + Doppler effect arising from peculiar motion) from the Doppler profile measured directly across the galaxy s disk and (2) by determining the actual dynamical centre of the galaxy. 

The process of estimating the global redshift component and estimating the dynamical center is termed the process of folding the rotation curve. Because of the very noisy nature of the data, this process is very far from trivial, especially if one is interested in accurate dynamical studies of spiral galaxies. 

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