The ALPINE-ALMA [CII] survey:Little to no evolution in the [CII]-SFR relation over the last 13 Gyr

The [CII] 158 mu 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 similar to 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 [CII] luminosity and the SFR over the entire redshift range from z similar to 4-8. ALPINE galaxies, which are both detected in [CII] 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 [CII] when the UV SFR is used. After accounting for dust-obscured star formation, by an amount of SFR(IR) approximate to 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 [CII] 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 [CII] measurements (detections and upper limits) do not behave very differently to the z similar to 4-6 data. We find a weak dependence of L([CII])/SFR on the Ly alpha equivalent width. Finally, we find that the ratio L([CII])/L-IR similar to (1-3) x 10(-3) for the ALPINE sources, comparable to that of "normal" galaxies at lower redshift. Our analysis, which includes the largest sample (similar to 150 galaxies) of [CII] measurements at z>4 available so far, suggests no or little evolution of the [CII]-SFR relation over the last 13 Gyr of cosmic time.