The morphological decomposition of Abell 868

We report on the morphological luminosity functions (LFs) and radial profiles derived for the galaxy population within the rich cluster Abell 868 (z = 0.153) based purely on Hubble Space Telescope imaging in F606W. We recover Schechter functions (-24.0 < M_F606W - 5 log h_0.65 < -16.0) within a 0.65h_0.65 Mpc radius for early (E/S0), mid (Sabc), and late (Sd/Irr) type galaxies of 1. M_all* - 5 log h _0.65 = -22.4_-0.6^+0.6, α_all = -1.27_-0.2^+0.2; 2. M_E/S0* - 5 log h _0.65 = -21.6_-0.6^+0.6, α_E/S0 = -0.5_-0.3^+0.2; 3. M_Sabc* - 5 log h _0.65 = -21.3_-0.9^+1.0, α_Sabc = -1.2_-0.2^+0.2; and 4. M_Sd/Irr* - 5 log h_0.65 = -17.4_-0.7^+0.7, α _Sd/Irr = -1.4_0.5^+0.6. The early, mid, and late types are all consistent with the recent field morphological LFs based on recent analysis of the Sloan Digital Sky Survey Early Data Release. From a detailed error analysis, including clustering of the background population, we note that improved statistics can only come from combining data from many clusters. We also examine the luminosity-density and number-density profiles as a function of morphology and draw the following conclusions: (1) the galaxies responsible for the steep faint-end slope are predominantly of late-type morphology; (2) the cluster core is dominated by elliptical galaxies; (3) the core is devoid of late-type systems; (4) the luminosity density as a function of morphological type is skewed toward early types when compared with the field; (5) up to half of the elliptical galaxies may have formed from the spiral population through core disk-destruction process(es). We believe the most plausible explanation is the conventional one that late types are destroyed during transit through the cluster core and that mid types are converted into early types through a similar process, which destroys the outer disk and results in a more tightly bound population of core elliptical galaxies.