Mass to luminosity ratio

Mass-to-luminosity Ratios and Models of Physical Evolution of Stellar Populations... 

The next problem was to find internally constitent values of physical parameters of stellar populations of different age and composition. For this purpose I developed a model of physical evolution of stellar populations (Einasto 1971). When I started the modelling of physical evolution of galaxies I was not aware of similar work by Beatrice Tinsley (1968). When my work was almost finished I had the opportunity to read the PhD thesis by Beatrice. Both studies were rather similar, in some aspects my model was a bit more accurate (evolution was calculated as a continuous function of time whereas Beatrice found it for steps of 1 Gyr, also some initial parameters were different). Both models used the evolutionary tracks of stars of various composition (metallicity) and age, and the star formation rate by Salpeter (1955). I accepted a low-mass limit of star formation, Mo 0.03 Msun, whereas Beatrice used a much lower mass limit to get higher mass-to-luminosity ratio for elliptical galaxies. My model... 

Groups of galaxies are bound with conventional masses the mean mass-to-luminosity ratios of groups are 4 and 30 for spiral and elliptical dominated groups, respectively ... 

By the end of 1970s most objections against the dark matter hypothesis were rejected. In particular, luminous populations of galaxies have found to have lower mass-to-luminosity ratio than expected previously, thus the presence of extra dark matter both in galaxies and clusters has been confirmed. However, the nature of dark matter and its purpose was not yet clear. Also it was not clear how to explain the Big Bang nucleosynthesis constraint on the low density of matter, and the smoothness of the Hubble flow. 

The story of the global dark matter also spans many decades. It began with the work by Zwicky (1933) on the Coma cluster, was continued with the study by Kahn and Woltjer (1959) on the dynamics of the Galaxy-M31 system, and statistical determinations of masses and mass-to-luminosity ratios of pairs, groups and clusters of galaxies. For some reason, these studies did not awake the attention of the astronomical community. However, the awareness of the presence of a controversy with masses of galaxies and galaxy systems slowly increased. 

The chemical analysis has revealed that rather low C/O ratios are found in metal-poor extragalactic carbon stars, as found for galactic carbon stars of the solar vicinity. Furthermore, the three analyzed stars show similar s-elements enhancements [ls/Fe]=0.8-1.3 and [hs/Fe]=l.l-1.7. This leads to new constraints for evolutionary models. For instance, the derived C/O and 13C/12C ratios are lower than model predictions at low metallicity. On the contrary, theoretical predictions of neutrons exposures for the production of the s-elements are compatible with observations (see Fig. 1). Finally, from their known distances, we have estimated the luminosities and masses of the three stars. It results that SMC-B30 and Sgr-C3 are most probably intrinsic carbon stars while Sgr-Cl could be extrinsic. 

For premixed fuel-air systems, results are reported in various terms that can be related to a critical equivalence ratio at which the onset of some yellow flame luminosity is observed. Premixed combustion studies have been performed primarily with Bunsen-type flames [52, 53], flat flames [54], and stirred reactors [55, 56], The earliest work [57, 58] on diffusion flames dealt mainly with axisymmetric coflow (coannular) systems in which the smoke height or the volumetric or mass flow rate of the fuel at this height was used as the correlating parameter. The smoke height is considered to be a measure of the fuel s particulate formation and growth rates but is controlled by the soot particle bumup. The specific references to this early work and that mentioned in subsequent paragraphs can be found in Ref. [50],... 

The sdO classification causes some confusion because class members span a range of 2 dex in surface gravity (and hence in luminosity-to-mass ratio). PG classifications do not demonstrate this, but a finer scheme is more successful [154]. Higher-gravity stars lie close to the extreme horizontal-branch / helium main-sequence. A link with the He-sdB stars seems likely (Fig. 33). 

Although the M/L ratios are quite low for NGC 253 and M 82, they do not require that the energy source be non-stellar. Figure 7 shows the fraction of the mass that must be converted into stars in order to obtain a particular M/L ratio. The distribution of these stars is assumed to follow the Salpeter (1959) "initial" luminosity... 

Detailed studies have provided solid evidence for the existence of dark halos around disk galaxies of any morphological type, luminosity, and environmoit (e.g., Rubin et cU. 1985 Kent 1988). Nevertheless, quantitative assessmmt of the size and importance of the various dynamical components (e.g., disk, bulge, halo, and their M/L ratios) suffers from the limited validity of certain premises. One questionable assumption is that of constant M/L ratios for the bulge and disk components. Another question is about the mass distribution inferred from optical emission-line rotation curves, which are related to the kinematics of the ionized gas, so that rotation curves in bulge-dominated regions may not measure true rotational velocities (Kent 1988 Kormendy Westpfahl 1989). 

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