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Register a new userThe K Band Luminosity Function in Galaxy Clusters to z ~ 1
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R. De Propris
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We present $K$-band luminosity functions for galaxies in a heterogeneous sample of 38 clusters at $0.1 < z < 1$. Using infrared-selected galaxy samples which generally reach 2 magnitudes fainter than the characteristic galaxy luminosity $L^*$, we fit Schechter functions to background-corrected cluster galaxy counts to determine $K^*$ as a function of redshift. Because of the magnitude limit of our data, the faint-end slope $alpha$ is fixed at -0.9 in the fitting process. We find that $K^*(z)$ departs from no-evolution predictions at $z > 0.4$, and is consistent with the behavior of a simple, passive luminosity evolution model in which galaxies form all their stars in a single burst at $z_f = 2 (3)$ in an $H_0 = 65 km/s Mpc^{-1}, Omega_M = 0.3, Omega_{Lambda}=0.7 (0)$ universe. This differs from the flat or negative infrared luminosity evolution which has been reported for high redshift field galaxy samples. We find that the observed evolution appears to be insensitive to cluster X-ray luminosity or optical richness, implying little variation in the evolutionary history of galaxies over the range of environmental densities spanned by our cluster sample. These results support and extend previous analyses based on the color evolution of high redshift cluster E/S0 galaxies, indicating not only that their stellar populations formed at high redshift, but that the assembly of the galaxies themselves was largely complete by $z approx 1$, and that subsequent evolution down to the present epoch was primarily passive.
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We measured the K-band luminosity function using a complete sample of 4192 morphologically-typed 2MASS galaxies with 7 < K < 11.25 mag spread over 2.12 str. Early-type (T < -0.5) and late-type (T > -0.5) galaxies have similarly shaped luminosity functions, alpha_e=-0.92+/-0.10 and alpha_l=-0.87+/-0.09. The early-type galaxies are brighter, M_*e=-23.53+/-0.06 mag compared to M_*l=-22.98pm0.06 mag, but less numerous, n_*e=(0.0045+/-0.0006)h^3/Mpc^3 compared to n_*l=(0.0101+/-0.0013)h^3/Mpc^3 for H_0=100h km/s Mpc, such that the late-type galaxies slightly dominate the K-band luminosity density, j_late/j_early=1.17+/-0.12. Our morphological classifications are internally consistent, consistent with previous classifications and lead to luminosity functions unaffected by the estimated uncertainties in the classifications. These luminosity functions accurately predict the K-band number counts and redshift distributions for K < 18 mag, beyond which the results depend on galaxy evolution and merger histories.
We derive the rest-frame $K$-band luminosity function for galaxies in 32 clusters at $0.6 < z < 1.3$ using deep $3.6mu$m and $4.5mu$m imaging from the Spitzer Space Telescope InfraRed Array Camera (IRAC). The luminosity functions approximate the stellar mass function of the cluster galaxies. Their dependence on redshift indicates that massive cluster galaxies (to the characteristic luminosity $M^*_K$) are fully assembled at least at $z sim 1.3$ and that little significant accretion takes place at later times. The existence of massive, highly evolved galaxies at these epochs is likely to represent a significant challenge to theories of hierarchical structure formation where such objects are formed by the late accretion of spheroidal systems at $z < 1$.
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