M5 Galaxies

Topic

This model focuses on the entire population of galaxies and their star-formation activity. These galaxies are classified both morphologically—as spirals, ellipticals, or irregulars—and physically, based on their color, star-formation rate, and stellar mass.

The Schechter luminosity function provides a statistical description of this population: above a characteristic luminosity, the number of galaxies drops off exponentially, whereas below that luminosity, it follows a much shallower power law; this difference in behavior means that faint galaxies are abundant, while extremely luminous ones become rare beyond that characteristic scale.

Within this population, the most massive galaxies retain their metals far more efficiently than lighter ones; consequently, greater mass leads to greater chemical enrichment retention, meaning mass and chemical enrichment grow in tandem.

Furthermore, for a given stellar mass, these galaxies follow two very different evolutionary paths: a star-forming "main sequence," where the star-formation rate increases with stellar mass according to a relationship that is smoother than simple proportionality; and a separate population of quiescent galaxies that have effectively ceased forming stars. Thus, the journey from the initial galaxy population to these two distinct outcomes—encompassing the Schechter luminosity function and the metal-retention mechanism linking mass to chemical enrichment—demonstrates how a single starting ingredient (the mass at a galaxy's birth) ultimately gives rise to vastly different shapes, colors, and star-formation fates.

ID:4103