Missing [C II] emission from early galaxies

Journal
Date Issued
2020
Author(s)
Carniani, S.
•
Ferrara, A.
•
Maiolino, R.
•
•
Gallerani, S.
•
•
Kohandel, M.
•
Lupi, A.
•
Pallottini, A.
•
•
•
DOI
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 > 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 (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.
Volume
499
Issue
4
Start page
5136
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2020MNRAS.499.5136C
Rights
open.access
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