Missing [C ii ] emission from early galaxies

Monthly Notices of the Royal Astronomical Society, vol. 499, pp. 5136–5150

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 > 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.

Authors 12

1. Stefano Carniani corresponding

   Scuola Normale Superiore

   Affiliation as printed

   Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy

2. Andrea Ferrara

   Scuola Normale Superiore

   Affiliation as printed

   Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy

3. R. Maiolino

   University of Cambridge

   Affiliation as printed

   Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

   Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

4. M. Castellano

   Astronomical Observatory of Rome · National Institute for Astrophysics

   Affiliation as printed

   INAF – Osservatorio Astronomico di Roma, Via Frascati 33, I-00078 Monte Porzio Catone (RM), Italy

5. S. Gallerani

   Scuola Normale Superiore

   Affiliation as printed

   Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy

6. A. Fontana

   Astronomical Observatory of Rome · National Institute for Astrophysics

   Affiliation as printed

   INAF – Osservatorio Astronomico di Roma, Via Frascati 33, I-00078 Monte Porzio Catone (RM), Italy

7. M. Kohandel

   Scuola Normale Superiore

   Affiliation as printed

   Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy

8. Alessandro Lupi

   Scuola Normale Superiore

   Affiliation as printed

   Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy

9. A. Pallottini

   Scuola Normale Superiore

   Affiliation as printed

   Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy

10. L. Pentericci

    Astronomical Observatory of Rome · National Institute for Astrophysics

    Affiliation as printed

    INAF – Osservatorio Astronomico di Roma, Via Frascati 33, I-00078 Monte Porzio Catone (RM), Italy

11. Livia Vallini Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, PO Box 9500, NL-2300 RA Leiden, the Netherlands

12. E. Vanzella

    Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics

    Affiliation as printed

    INAF – Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, I-40129 Bologna, Italy