Missing [C <scp>ii</scp>] emission from early galaxies
Stefano Carniani, Andrea Ferrara, R. Maiolino, M. Castellano, S. Gallerani, A. Fontana, M. Kohandel, Alessandro Lupi, A. Pallottini, L. Pentericci, L. Vallini, E. Vanzella
Abstract
ABSTRACT ALMA observations have revealed that [C ii] 158 μm line emission in high-z galaxies is ≈2–3 × more extended than the UV continuum emission. Here we explore whether surface brightness dimming (SBD) of the [C ii] line is responsible for the reported [C ii] deficit, and the large $L_{\rm [O\, \small {III}]}/L_{\rm [C\, \small {II}]}$ luminosity ratio measured in early galaxies. We first analyse archival ALMA images of nine z &gt; 6 galaxies observed in both [C ii] and [O iii]. After performing several uv-tapering experiments to optimize the identification of extended line emission, we detect [C ii] emission in the whole sample, with an extent systematically larger than the [O iii] emission. Next, we use interferometric simulations to study the effect of SBD on the line luminosity estimate. About 40 per cent of the extended [C ii] component might be missed at an angular resolution of 0.8 arcsec, implying that $L_{\rm [C\, \small {II}]}$ is underestimated by a factor ≈2 in data at low (&lt;7) signal-to-noise ratio. By combining these results, we conclude that $L_{\rm [C\, \small {II}]}$ of z &gt; 6 galaxies lies, on average, slightly below the local $L_{\rm [C\, \small {II}]}-\mathrm{ SFR}$ relation (Δz = 6–9 = −0.07 ± 0.3), but within the intrinsic dispersion of the relation. SBD correction also yields $L_{\rm [O\, \small {III}]}/L_{\rm [C\, \small {II}]}\lt 10$, i.e. more in line with current hydrodynamical simulations.