4 Comparison of the ALMA and Herschel - ESO

abundances and H 2
densities. A typical Spectral Energy Distribution (SED) is shown in Fig.
1. We also show the operational wavelength ranges of the two instruments.
Both Herschel and ALMA will come into operation at similar times. ALMA should be
completed in 2012, but “early science” operation will begin well before this. The official
launch date of the Herschel satellite is early 2008 and it has an expected lifetime of more
than 3 years. Thus there should be a period during which both are in operation together.
This will allow for the simultaneous measurement of astronomical sources with rapid time
variations. However, even if the measurements do not overlap, one can combine results from
these facilities to improve the analysis of sources with slow or no time variations.
Hence it is important to establish regions of common ground and to develop strategies
that will optimise the opportunities to exploit the distinctive features of each instrument
and define combined programmes aimed at specific science goals. This report reviews the
capabilities of each instrument and compares their performance and approach to common
observational techniques in Chapters 3 and 4. If the observational areas of the two instruments
are to overlap, some form of common calibration is desirable and methods for this are
discussed in Chapter 5, before specific examples of potential common science programmes
are given in Chapter 6. Recommendations for the future, addressed separately and jointly
to ESO and ESA, are presented in Chapter 8.
4