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--- courses:ast403:galaxy-luminosity-function [2026/02/14 06:44] – shuvo
+++ courses:ast403:galaxy-luminosity-function [2026/02/14 06:47] (current) – shuvo
@@ Line 11: / Line 11: @@
 The function is defined by three primary parameters as illustrated in the figure above:
-$L^*$ (Characteristic Luminosity): The "break" luminosity where the function transitions from power-law to exponential decay. In the blue band, $L_B^* \approx 1.2 \times 10^{10} h^{-2} L_\odot$, which is comparable to the luminosity of the Milky Way.
+**$L^*$ (Characteristic Luminosity):** The "break" luminosity where the function transitions from power-law to exponential decay. In the blue band, $L_B^* \approx 1.2 \times 10^{10} h^{-2} L_\odot$, which is comparable to the luminosity of the Milky Way.
-$\alpha$ (Faint-end Slope): This defines the abundance of faint galaxies. Typical values are $\alpha \approx -1.07$ for blue-band surveys. If $\alpha \leq -1$, the total number density of galaxies is formally infinite, though the physical function is cut off at a minimum luminosity.
+**$\alpha$ (Faint-end Slope):** This defines the abundance of faint galaxies. Typical values are $\alpha \approx -1.07$ for blue-band surveys. If $\alpha \leq -1$, the total number density of galaxies is formally infinite, though the physical function is cut off at a minimum luminosity.
-$\Phi^*$ (Normalization): The number density of galaxies per Mpc$^3$, typically found to be $\Phi^* \approx 1.6 \times 10^{-2} h^3 \text{ Mpc}^{-3}$.
+**$\Phi^*$ (Normalization):** The number density of galaxies per Mpc$^3$, typically found to be $\Phi^* \approx 1.6 \times 10^{-2} h^3 \text{ Mpc}^{-3}$.
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 The "universal" Schechter function is often a simplification, as the luminosity distribution depends heavily on morphology and environment:
-//Color Bimodality:// The galaxy population exhibits a bimodal distribution in color-magnitude space. Red sequence galaxies (older, early-type) dominate at high luminosities, while the blue cloud (star-forming, late-type) dominates at lower luminosities.
+**Color Bimodality:** The galaxy population exhibits a bimodal distribution in color-magnitude space. Red sequence galaxies (older, early-type) dominate at high luminosities, while the blue cloud (star-forming, late-type) dominates at lower luminosities.
-{{ :courses:ast403:galaxy_color.jpg?600 |Fig2:  }}
+[{{ :courses:ast403:galaxy_color.jpg?600 |Fig2: The density of galaxies in color–magnitude space.The color of ∼ 70 000 galaxies with redshifts $0.01 \le z \le 0.08$ from the Sloan Digital Sky Survey is measured by the rest-frame $u−r$, i.e., after a (small) correction for their redshift was applied.}}]
 **Environmental Dependence:** In rich clusters, the luminosity function is dominated at the bright end by ellipticals and S0 galaxies, and at the faint end by dwarf ellipticals ($dE$). Clusters often contain a cD galaxy at the center that is significantly brighter than the Schechter $L^*$ predicts, representing a "light excess" at large radii.