Volume 562, February 2014
|Number of page(s)||10|
|Published online||04 February 2014|
High-resolution C+ imaging of HDF850.1 reveals a merging galaxy at z = 5.185⋆
Institut de Radioastronomie Millimétrique, Domaine
2 ALMA SCO, Alonso de Cordova 3107 Vitacura, Santiago, Chile
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Received: 22 August 2013
Accepted: 12 December 2013
New high-resolution maps with the IRAM interferometer of the redshifted C+ 158 μm line and the 0.98mm dust continuum of HDF850.1 at z = 5.185 show the source to have a blueshifted northern component and a redshifted southern component, with a projected separation of 0.3′′, or 2 kpc. We interpret these components as primordial galaxies that are merging to form a larger galaxy. We think it is the resulting merger-driven starburst that makes HDF850.1 an ultraluminous infrared galaxy, with LIR ~ 1013 L⊙. The observed line and continuum brightness temperatures and the constant line-to-continuum ratio across the source imply (1) high C+ line optical depth, (2) a C+ excitation temperature of the same order as the dust temperature, and (3) dust continuum emission that is nearly optically thick at 158 μm. These conclusions for HDF850.1 probably also apply to other high-redshift submillimeter galaxies and quasar hosts in which the C+ 158 μm line has been detected, as indicated by their roughly constant C+-to-158 μm continuum ratios, in sharp contrast to the large dispersion in their C+-to-FIR luminosity ratios. In brightness temperature units, the C+ line luminosity is about the same as the predicted CO(1–0) luminosity, implying that the C+ line can also be used to estimate the molecular gas mass, with the same assumptions as for CO.
Key words: galaxies: high-redshift / galaxies: kinematics and dynamics / galaxies: ISM / galaxies: individual: HDF850.1
The spectra of Fig. 2 are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/562/A35
© ESO, 2014
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