R. Scaramella

Luminosity function of clusters of galaxies

The composite galaxy luminosity function (hereafter LF) of 39 Abell clusters of galaxies is derived by computing the statistical excess of galaxy counts in the cluster direction with respect to control elds. Due to the wide eld coverage of the digitised POSS-II plates, we can measure eld counts around each cluster in a fully homogeneous way. Furthermore, the availability of virtually unlimited sky coverage allows us to directly compute the LF errors without having to rely on the estimated variance of the background. The wide eld coverage also allows us to derive the LF of the whole cluster, including galaxies located in the cluster outskirts. The global composite LF has a slope 1:1 0:2 with minor variations from blue to red lters, and M 21:7; 22:2; 22: 4m ag (H0 =5 0 km s 1 Mpc 1 )i ng;r and i lters, respectively (errors are detailed in the text). These results are in quite good agreement with several previous determinations and in particular with the LF determined for the inner region of a largely overlapping set of clusters, but derived making use of a completely dierent method for background subtraction. The similarity of the two LFs suggests the existence of minor dierences between the LF in the cluster outskirts and in the central region, or a negligible contribution of galaxies in the cluster outskirts to the global LF.

Cataloging of the Digitized Poss-II: Initial Scientific Results

The Second Palomar Sky Survey (POSS-II) is now nearing completion. It will cover the entire northern sky with 894 fields (6.5° square) at 5° spacings, with no gaps in the coverage. Plates are taken in three bands: IIIa-J + GG395, λ eff ~ 480 nm; IIIa-F + RG610, λ eff ~ 650 nm; and IV-N + RG9, λ eff ~ 850 nm. Typical limiting magnitudes reached are B J ~ 22.5, R F ~ 20.8, and I N ~ 19.5, i.e., ~ 1 m – 1.5 m deeper than the POSS-I. The image quality is improved relative to the POSS-I, and is comparable to the southern photographic sky surveys. For more details, see Reid et al. (1987), and Reid & Djorgovski (1993).