4 Comparison of the ALMA and Herschel - ESO

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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. 48
8.4 Calibration To compare the Herschel and ALMA data, one must have accurate calibration. This will require a special measurement and source modelling programme. For ALMA, a science specification is to have absolute amplitude errors of 3% in the mm and 5% in the sub-mm. Thus any calibration source models must have accuracies of better than 1%. The limitations of ALMA and Herschel are very different. The PACS and SPIRE detectors are easily saturated. Thus it is likely that one would use the fainter, smaller outer planets or asteroids. Since the bolometer bandwidths are much larger than the ALMA bandwidths, common calibrations require a very accurate model of the sources including possible time variations. For Herschel HIFI and ALMA, there are common regions of the spectrum. However, the choice of spectral line calibration sources is more complex than with PACS or SPIRE. One may have to use either very small spectral line sources that are unresolved by ALMA, but bright enough to allow Herschel measurements, or (more likely) carry out a complete imaging of slightly extended calibration sources with ALMA. The first choice is limited by signal-to-noise ratios, while the second requires a larger investment in observing time with ALMA. 8.5 Data Archives ALMA data alone and Herschel data alone will each be a great step forward. Combined ALMA-Herschel datasets will be a tremendous advance. Allowing open access to data of general interest by means of Virtual Observatory (VO) is the only way for an optimum exploitation of Herschel data and subsequent ALMA observations. ALMA and Herschel data must be VO compliant. There must be a clear policy of data rights since there will be only a short time interval in which common measurements are possible. 8.6 Action Items for the Organisations ESA: There is a need to plan for Herschel surveys for regions within the ALMA elevation range. The calibration measurements must be carried out so that there are secure comparisons with ALMA continuum and spectral line data. The 75 µm band of PACS Herschel is needed to determine SEDs. These surveys will be unique; this wavelength is a fundamental input for the discrimination between AGN phenomena and starbursts in galaxies. For an efficient synergy, ESA should devote a significant part of Herschel time to Legacy projects, ie, projects of wide interest for the community, starting soon after the science verification phase or very early in Herschel’s lifetime. This would have to be the case for Herschel surveys of galactic and extragalactic sources, in continuum and spectroscopy. A targeted survey of Spitzer sources for ALMA follow-ups is needed. Such a survey would include debris disks, protostars, and galaxies. ESA must provide wide access to the data, 49
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Report by the ESA-ESO Working Group
Page 5 and 6: Contents 1 Executive Summary ......
Page 9 and 10: 1 Executive Summary The Herschel Sa
Page 11 and 12: 2 Introduction The Herschel satelli
Page 13 and 14: 3 Descriptions of Herschel and ALMA
Page 15 and 16: Table 1: ALMA Antenna Arrays and Co
Page 17 and 18: 3.2 Herschel Herschel is a cornerst
Page 19: Table 6: Some Characteristics of th
Page 22 and 23: Figure 6: A three-dimensional plot
Page 24 and 25: Figure 8: A plot of the Herschel HI
Page 27 and 28: 5 Common Calibration of ALMA and He
Page 29 and 30: 6 Specific Examples of Synergies Be
Page 31 and 32: 6.3 High Redshift Objects During th
Page 33 and 34: eview) have also revealed a new cla
Page 35 and 36: In addition to emission lines from
Page 37 and 38: y interactions. Consider the nearby
Page 39 and 40: Figure 12: Data for IC10. The integ
Page 41 and 42: matter interacts with the powerful
Page 43 and 44: In DRSP contribution 2.1.2, Kinetic
Page 45 and 46: The Orion KL region is one of the n
Page 47 and 48: degrees. The GLIMPSE survey is bein
Page 49 and 50: An example is DRSP contribution 3.3
Page 51 and 52: Figure 18: A schematic of the analy
Page 53: 7 Summary The PACS and SPIRE bolome
Page 58 and 59: calibration files and to a pipeline
Page 60 and 61: SWAS — Submillimeter Wave Astrono
Page 62 and 63: Falgarone, E., Hily-Blant, P., Pine
Page 64: Wilson, C. D., 2005 in Proc. of The
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