4 Comparison of the ALMA and Herschel - ESO

The full ALMA will be in operation toward the end of Herschel’s life, so the data rights for
Herschel may have expired. There is little need to have simultaneous measurement periods
except for the cases as noted above. It is possible that Herschel will detect interesting but
heavily obscured objects for which there can be no redshift measurements. Here there would
have to be a need for quick responses from the ALMA Observatory to measure redshifts
using CO rotational lines.
8.2 Supporting Observations
The best approach is to carry out lower angular resolution preparatory surveys of the
GOODS, HDF-S and/or CDFS and galactic fields in the millimetre, sub-mm or far infrared.
One possibility would be very deep integrations for extragalactic sources with the 12 m
APEX antenna and the LABOCA bolometer camera. Larger single dishes with large bolometer
cameras would provide better sensitivity, higher mapping speed, and also lower
source confusion levels. Possible choices might be the James Clerk Maxwell (JCMT) with
the SCUBA-2 camera. It is possible that the Large Millimeter Telescope (LMT), now under
construction, will be in operation soon. The LMT with a bolometer camera would provide
an excellent finding survey for ALMA. Further in the future, the use of the Extremely Large
Telescope, ELT, in the sub-mm range would also be a possible choice if the ELT has horizon
limits similar to ALMA’s. For galactic sources, one could use the results of appropriate
Spitzer Legacy programmes to image protostars or debris disks.
8.3 Supporting Data
There is a need to establish molecular collision rates, radiative transfer algorithms and chemical
reaction rates. For some molecules this is included in the EC Framework Programme 6
The Molecular Universe. The scope of this programme is limited, and much more is needed.
The Molecular Universe Programme should serve as a model for future undertakings.
One of the most important items for ALMA and Herschel is a completely automated form of
data reduction. There will be very large three-dimensional data cubes of large collections of
spectral line images (ie, two coordinates and velocity) or large two-dimensional broadband
images from ALMA. With combined ALMA and Herschel datasets, the broadband results
also form a data cube, with the third dimension being wavelength. These datasets may have
sizes of more than a few million data-points; this precludes any detailed analysis using simple
position-by-position analysis. The obvious step is to compare such datasets with models
in an automated way. Clearly for specific regions one would start with general geometries,
or pre-existing models based on lower angular resolution data, iterate the model until convergence,
and then check whether the model is realistic in some sense. There is no general
data reduction process available now, nor is there financial support for such a development.
This will have to be the next step in the analysis of combined Herschel-ALMA datasets.
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