Missing [C II] emission from early galaxies

Jun 16, 2020
15 pages
Published in:
  • Mon.Not.Roy.Astron.Soc. 499 (2020) 4, 5136-5150
  • Published: Nov 21, 2020
e-Print:
DOI:

Citations per year

202020212022202320240246810
Abstract: (Oxford University Press)
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[OIII]/L[CII]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[CII]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[CII]L_{\rm [C\, \small {II}]}| of z > 6 galaxies lies, on average, slightly below the local |L[CII]SFRL_{\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[OIII]/L[CII]<10L_{\rm [O\, \small {III}]}/L_{\rm [C\, \small {II}]}\lt 10|⁠, i.e. more in line with current hydrodynamical simulations.
  • galaxies: evolution
  • galaxies: formation
  • galaxies: high-redshift
  • galaxies: ISM