What does "Effective Radius" mean?

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The effective radius is a term used to describe the size of a galaxy. It helps scientists understand how galaxies grow and change over time. This measurement is important because it connects to various other features of galaxies, like their brightness and mass.

When scientists talk about the effective radius, they often look at different wavelengths of light, such as optical and near-infrared. They found that the effective radius can be larger than the radius calculated from the mass of the stars in the galaxy, and this difference changes based on the light wavelength. For example, in certain light bands, the effective radius can be up to 58% larger than the stellar mass radius.

The presence of dust in a galaxy also affects the effective radius measurements. When images are taken of galaxies with dust, they appear larger compared to images taken with less dust. However, this effect is usually small.

Studies have shown that the way stars are distributed within a galaxy plays a big role in the effective radius. Additionally, the way light is absorbed by dust is a smaller factor.

Comparisons with observational data reveal that there can be significant differences in effective radius values for different types of galaxies, especially between blue and red galaxies. The sizes of blue galaxies can be notably different from what models predict, which can lead to more questions about their formation and growth.

Overall, the effective radius is a key piece of information for scientists studying the life cycle and characteristics of galaxies.