An Accurate Position for HDF 850.1: The Brightest Submillimeter Source
  in the Hubble Deep Field-North
  We report a highly significant Submillimeter Array (SMA) detection of the
prototypical submillimeter source HDF 850.1, which is the brightest
submillimeter source in the Hubble Deep Field-North proper. The detection
yields an extremely precise position of RA(2000)=12:36:51.99 and
Dec(2000)=+62:12:25.83 with a 1-sigma positional uncertainty of 0.17 arcsec.
The position is consistent with the location of a millimeter wavelength
interferometric detection and with the locations of weak VLA detections at 1.4
and 8.4 GHz, but it is not consistent with any previous optical/near-infrared
identifications. The source appears pointlike at the 2 arcsec resolution of the
SMA, and the detected flux of 7.8+/-1.0 mJy is consistent with the measured
SCUBA fluxes. We tabulate fluxes and limits on HDF 850.1 at other wavelengths.
Our redshift estimate for HDF 850.1 based on the radio through mid-infrared
measurements is z=4.1. The faintness of the source at optical/near-infrared
wavelengths and the high estimated redshift suggest that HDF 850.1 may be an
analog of the brighter submillimeter source GOODS 850-5, which is also thought
to be at z>4. The fact that a source like HDF 850.1 should have appeared in one
of the very first blank-field SCUBA observations ever made suggests that such
high-redshift sources are quite common. Thus, we are led to conclude that
high-redshift star formation is dominated by giant dusty star-forming galaxies,
just as it is at lower redshifts.
