| Abstract |
We present sensitive phase-referenced Very Long Baseline Interferometry
(VLBI) results on the radio continuum emission from the z = 1.87
luminous submillimeter galaxy (SMG) GOODS 850-3. The observations were
carried out at 1.4 GHz using the High-Sensitivity Array (HSA). Our
sensitive tapered VLBI image of GOODS 850-3 at 0farcs47 × 0farcs34
(3.9 × 2.9 kpc) resolution shows a marginally resolved continuum
structure with a peak flux density of 148 ± 38 μJy
beam-1, and a total flux density of 168 ± 73
μJy, consistent with previous Very Large Array and MERLIN
measurements. The deconvolved size of the source is
0farcs27(±0farcs12) × <0farcs23, or 2.3(±1.0)
× <1.9 kpc, and the derived intrinsic brightness temperature is
>(5 ± 2) × 103 K. The radio continuum
position of this galaxy coincides with a bright and extended
near-infrared source that nearly disappears in the deep Hubble Space
Telescope optical image, indicating a dusty source of nearly 9 kpc in
diameter. No continuum emission is detected at the full VLBI resolution
(13.2 × 7.2 mas, 111 × 61 pc), with a 4σ point source
upper limit of 26 μJy beam-1, or an upper limit to
the intrinsic brightness temperature of 4.7 × 105 K.
The extent of the observed continuum source at 1.4 GHz and the derived
brightness temperature limits are consistent with the radio emission
(and thus presumably the far-infrared emission) being powered by a major
starburst in GOODS 850-3, with a star formation rate of ~2500 M
sun yr-1. Moreover, the absence of any
continuum emission at the full resolution of the VLBI observations
indicates the lack of a compact radio-loud active galactic nucleus in
this z = 1.87 SMG.
Based in part on observations obtained at the Canada-France-Hawaii
Telescope (CFHT), which is operated by the National Research Council of
Canada, the Institut National des Sciences de l'Univers of the Centre
National de la Recherche Scientifique of France, and the University of
Hawaii, and the Subaru Telescope, which is operated by the National
Astronomical Observatory of Japan. |