Spiral galaxies evolution

Planetary nebulae (PNe) offer the opportunities 1) to study stellar nucleosynthesis in the advanced phases of stellar evolution of stars in the wide mass range - -O. S to Mq and 2) to probe radial and as well horizontal/vertical chemical gradients in spiral galaxies by the time of formation of their progenitors. 

As a consequence chemical abundances in PNe are of primary importance for the chemical evolution of spiral galaxies, including our own and related topics. 

The IRAS galaxies provided some of the earliest evidence from redshift surveys, and from source counts as a function of observed flux, that the spiral galaxy population has undergone evolution (ORS see Fig. 12.2). This result is analogous to similar evidence from source counts of radio galaxies and quasars, as well as quasar redshifts, and a correlation that has been observed between radio and infrared luminosity suggests that the evolution could be similar in both cases. Typical simple models for such evolution include luminosity evolution according to... 

Thus it appears that spiral galaxies are constrained to exist one of a set of discrete state planes in the three-dimensional (M, S, a) space. This then gives rise to one of two possibilities either a spiral galaxy is born on one of these planes, and remains on this plane over its whole evolution or a spiral galaxy remains on one of these planes for very long periods, with the possibility of transiting to other planes in very short periods of time. 

The radial luminosity profiles of disks in spiral galaxies csin be described by an exponential law and are thus characterized by two parameters, the central stnface brightness (/uo) and the scalelength (h). Freeman (1970) foimd /to to be nearly constant in his sample of galaxies observed in the B band. This Freeman law has of course serious implications for theories on galaxy formation and evolution. 

Bob looks up. Stars are still being born now but more in the spiral arms than in the core. The core stars formed early in the Galaxy s history and are late in their evolution. The exploding stars, or supernovas, in the arms are kicking out heavy elements like carbon that were manufactured in the stars. ... 

The astrophysical problem of justifying on theoretical grounds the morphology of galaxies (spiral and eUiptical, with their different content in stars and gas), their chemical evolution (initial rapid enrichment of metals, i.e., any element heavier than hydrogen and helium), and, finally, the attempt to trace a classification based on different physical aspects of the evolution, has been tackled by employing the approach of cooperative systems. In these models a scenario is proposed where the large-scale dynamics are related to the local microscopic interactions. At the same time a macroscopic description (e.g., the interplay of various phases, the metallicity) is derived by means of few (stochastic) variables. 

In these lectures I present a highly opinionated review of the observed patterns of metallicity and element abundance ratios in nearby spiral, irregular, and dwarf elliptical galaxies, with connection to a number of astrophysical issues associated with chemical evolution. I also discuss some of the observational and theoretical issues associated with measuring abundances in H II regions and gas and stellar surface densities in disk galaxies. Finally, I will outline a few open questions that deserve attention in future investigations. 

The importance of this frequency for the resonance problem is that any force that is periodic on this time scale will produce a resonant interaction. For the more general problem of galactic structure, the points at which the perturbation frequency is the same as the epicyclic frequency are called the Lindblad resonances. These play a central role in density wave theory, which has been applied to a wide variety of astrophysical problems, including planetary ring systems, accretion disks, and the structure and evolution of spiral disk galaxies. 

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