The evolution of the luminosity functions in the FORS Deep Field from low to high redshift

Abstract

We present the redshift evolution of the restframe galaxy luminosity function (LF) in the red r � , i � ,a ndzbands, as derived from the FORS Deep Field (FDF), thus extending our earlier results to longer wavelengths. Using the deep and homogeneous I-band selected dataset of the FDF, we were able to follow the red LFs over the redshift range 0.5 < z < 3.5. The results are based on photometric redshifts for 5558 galaxies derived from the photometry in 9 filters and achieving an accuracy of ∆z/(zspec + 1) ≤ 0.03 with only ∼1% outliers. A comparison with results from the literature shows the reliability of the derived LFs. Because of the depth of the FDF, we can give relatively tight constraints on the faint-end slope α of the LF; the faint-end of the red LFs does not show a large redshift evolution and is compatible within 1σ to 2σ with a constant slope over the redshift range 0.5 < z < 2.0. Moreover, the slopes in r � , i � ,a ndzare very similar to a best-fitting value of α = −1.33 ± 0.03 for the combined bands. There is a clear trend of α to steepen with increasing wavelength: αUV&u� = −1.07 ± 0.04 → αg� &B = −1.25 ± 0.03 → αr� &i� &z� = −1.33 ± 0.03. We subdivided our galaxy sample into four SED types and determined the contribution of a typical SED type to the overall LF. We show that the wavelength dependence of the LF slope can be explained by the relative contribution of different SED-type LFs to the overall LF, as different SED types dominate the LF in the blue and red bands. Furthermore we also derived and analyzed the luminosity density evolution of the different SED types up to z ∼ 2. We investigated the evolution of M ∗ and φ ∗ by means of the redshift parametrization M ∗ (z) = M ∗ + a ln (1 + z )a ndφ ∗ (z) = φ ∗ (1 + z) b . Based on the FDF data, we found only a mild brightening of M ∗ (ar� ∼− 0.8, and ai� ,z� ∼− 0.4) and a decreasing φ ∗ (br� ,i� ,z� ∼− 0.6) with increasing redshift. Therefore, fromz �∼ 0. 5t oz �∼ 3 the characteristic luminosity increases by ∼0.8, ∼0.4, and ∼0.4 mag in the r � , i � ,a ndzbands, respectively. Simultaneously the characteristic density decreases by about 40% in all analyzed wavebands. A comparison of the LFs with semi- analytical galaxy formation models by Kauffmann et al. (1999) shows a similar result to the blue bands: the semi-analytical models predict LFs that describe the data at low redshift very well, but show growing disagreement with increasing redshifts.