Missing [C ii] emission from early galaxies. Issue 4 (14th October 2020)

• Record Type: Journal Article
• Authors: Carniani, S; Ferrara, A; Maiolino, R; Castellano, M; Gallerani, S; Fontana, A; Kohandel, M; Lupi, A; Pallottini, A; Pentericci, L; Vallini, L; Vanzella, E
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 499:Issue 4(2020)
• Page Start: 5136
• Page End: 5150
• Publication Date: 2020-10-14
• Subjects: galaxies: evolution -- galaxies: formation -- galaxies: high-redshift -- galaxies: ISM; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3178
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: ALMA observations have revealed that [C ii ] 158 μ m 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 > 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 (<7) signal-to-noise ratio. By combining these results, we conclude that $L_{\rm [C\, \small {II}]}$ of z > 6 galaxies lies, on average, slightly below the local $L_{\rm [C\, \small {II}]}-\mathrm{ SFR}$ relation (Δ z = 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.