Strong [CII] emission at high redshift

We report the detection of the [CII] 157.74 mu m fine-structure line in the lensed galaxy BRI 0952-0115 at z = 4.43, using the APEX telescope. This is the first detection of the [CII] line in a source with L(FIR) < 10(13) L(circle dot) at high redshift. The line is much stronger than previous [CII] detections at high-z (a factor of 5-8 higher in flux), partly due to the lensing amplification. The L([CII])/ L(FIR) ratio is 10(-2.9), which is higher than observed in local galaxies with similar infrared luminosities. Together with previous observations of [CII] at high redshift, our result suggests that the [CII] emission in high-redshift galaxies is enhanced relative to local galaxies with the same infrared luminosity. This finding may result from selection effects of the few current observations of [CII] at high redshift and, in particular, from non detections that may not have been published ( although the few published upper limits are still consistent with the [CII] enhancement scenario). If the trend is confirmed with larger samples, it would indicate that high-z galaxies are characterized by different physical conditions than for their local counterparts. Regardless of the physical origin of the trend, this effect would increase the potential of the [CII]158 mu m line to search and characterize high-z sources.