We present a new, robust measurement of the evolving rest-frame ultraviolet (UV) galaxy luminosity function (LF) over the key redshift range from z ≃ 2 to z ≃ 4. Our results are based on the high dynamic range provided by combining the Hubble Ultra Deep Field (HUDF), CANDELS/GOODS-South, and UltraVISTA/COSMOS surveys. We utilize the unparalleled multifrequency photometry available in this survey ‘wedding cake’ to compile complete galaxy samples at z ≃ 2, 3, 4 via photometric redshifts (calibrated against the latest spectroscopy) rather than colour–colour selection, and to determine accurate rest-frame UV absolute magnitudes (M1500) from spectral energy distribution (SED) fitting.
Our new rest-frame UV (1500 Å) galaxy LFs at z ≃ 2, 3 and 4. The (blue, green, red) data points indicate the values derived via the Vmax estimator, with the colour-matched solid lines showing the best-fitting Schechter functions. The values corresponding to the data points and their errors are tabulated in Table 2, while the values of the best-fitting Schechter parameters are given in Table 3, and plotted in Fig. 8. The vertical dashed line in each panel at M1500 = −18 is shown simply to indicate the typical absolute magnitude limit reached by previous studies at these redshifts, while the background shading indicates the absolute magnitude regimes in which the three different surveys (UltraVISTA/COSMOS, CANDELS/GOODS-S, HUDF) make the dominant contribution to our new measurement of the LF at each redshift. For comparison purposes, at each redshift we also show several LFs from the literature as indicated in the legend.
Our new determinations of the UV LF extend from M1500 ≃ −22 (AB mag) down to M1500 = −14.5, −15.5 and −16 at z ≃ 2, 3 and 4, respectively (thus, reaching ≃ 3–4 mag fainter than previous blank-field studies at z ≃ 2,3). At z ≃ 2, 3, we find a much shallower faint-end slope (α = −1.32 ± 0.03) than reported in some previous studies (α ≃ −1.7), and demonstrate that this new measurement is robust. By z ≃ 4, the faint-end slope has steepened slightly, to α = −1.43 ± 0.04, and we show that these measurements are consistent with the overall evolutionary trend from z = 0 to 8. Finally, we find that while characteristic number density (ϕ*) drops from z ≃ 2 to z ≃ 4, characteristic luminosity (M*) brightens by ≃ 1 mag. This, combined with the new flatter faint-end slopes, has the consequence that UV luminosity density (and hence unobscured star formation density) peaks at z ≃ 2.5–3, when the Universe was ≃ 2.5 Gyr old.
Further details can be found in Parsa, S. et al. 2015, MNRAS, 456, 3194