The Alpine-Alma [Cii] Survey: Little To No Evolution In The [Cii]-Sfr Relation Over The Last 13 Gyr

The [C II ] 158 μ m line is one of the strongest IR emission lines, which has been shown to trace the star formation rate (SFR) of galaxies in the nearby Universe, and up to z ∼ 2. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at 4.4 < z < 5.9, provides a new opportunity to examine this question with the first statistical dataset. Using the ALPINE data and earlier measurements from the literature, we examine the relation between the [C II ] luminosity and the SFR over the entire redshift range from z ∼ 4 − 8. ALPINE galaxies, which are both detected in [C II ] and in dust continuum, show good agreement with the local L ([CII])–SFR relation. Galaxies undetected in the continuum by ALMA are found to be over-luminous in [C II ] when the UV SFR is used. After accounting for dust-obscured star formation, by an amount of SFR(IR) ≈ SFR(UV) on average, which results from two different stacking methods and SED fitting, the ALPINE galaxies show an L ([CII])–SFR relation comparable to the local one. When [C II ] non-detections are taken into account, the slope may be marginally steeper at high- z , although this is still somewhat uncertain. When compared homogeneously, the z > 6 [C II ] measurements (detections and upper limits) do not behave very differently to the z ∼ 4 − 6 data. We find a weak dependence of L ([CII])/SFR on the Ly α equivalent width. Finally, we find that the ratio L ([CII])/ L IR ∼ (1 − 3) × 10 −3 for the ALPINE sources, comparable to that of “normal” galaxies at lower redshift. Our analysis, which includes the largest sample (∼150 galaxies) of [C II ] measurements at z > 4 available so far, suggests no or little evolution of the [C II ]–SFR relation over the last 13 Gyr of cosmic time.