CO(1-0) imaging of M51 with CARMA and NRO45
  We report the CO(J=1-0) observations of M51 using both the Combined Array for
Research in Millimeter Astronomy (CARMA) and the Nobeyama 45m telescope
(NRO45). We describe a procedure for the combination of interferometer and
single-dish data. In particular, we discuss (1) the joint imaging and
deconvolution of heterogeneous data, (2) the weighting scheme based on the
root-mean-square (RMS) noise in the maps, (3) the sensitivity and uv-coverage
requirements, and (4) the flux recovery of a combined map. We generate
visibilities from the single-dish map and calculate the noise of each
visibility based on the RMS noise. Our weighting scheme, though it is applied
to discrete visibilities in this paper, is applicable to grids in uv-space, and
this scheme may advance in future software development. For a realistic amount
of observing time, the sensitivities of the NRO45 and CARMA visibility data
sets are best matched by using the single dish baselines only up to 4-6
kilo-lambda (about 1/4-1/3 of the dish diameter). The synthesized beam size is
determined to conserve the flux between synthesized beam and convolution beam.
The superior uv-coverage provided by the combination of CARMA long baseline
data with 15 antennas and NRO45 short spacing data results in the high image
fidelity, which is evidenced by the excellent overlap between even the faint CO
emission and dust lanes in an optical HST image and PAH emission in an Spitzer
8 micron image.
