The technical justification guidelines are given in Section 6.3 of the ALMA Cycle 3 Proposer's Guide and Capabilities.
The technical justification is entered directly into the OT via a designated Technical Justification pane for each Science Goal. Any figures associated with the Technical Justification must be included in the Science Justification PDF file.
The Technical Justification pane shows the relevant parameters entered by the PI in other parts of the Science Goal, as well as a number of derived quantities such as signal-to-noise ratio and dynamic range. The Technical Justification is entered in a free-format text box and should fully justify the technical aspects of the requested observations, with particular attention paid to those parameters that most directly affect the Science Goal time estimate. The text is limited to 4000 characters per Science Goal and should address the following aspects:– Sensitivity: relevant parameters to discuss here include the source flux, angular size, width of the spectral lines, desired spectral resolution/channel width and significance (i.e., signal-to-noise ratio). PIs should be aware that the sensitivity returned by the ALMA Sensitivity Calculator may not always be achievable. For instance, this can occur when the field of view contains a very bright source. Similarly, bright lines in the spectra can also make it very difficult to achieve a theoretical rms, as can a crowded spectrum or faint lines sitting on top of bright continua. Low or very high signal-to-noise ratios must be justified.
– Imaging: if science targets are to be mapped, the most important consideration will be whether the imaging algorithms are able to reconstruct the various source components. The uv-coverage for Cycle 3 is such that even snapshot images will be able to produce good maps of most sources. In the rare instances this is not the case (e.g. a very complex but bright source), the OT's sensitivity-based time estimate can be overridden, but this must be explicitly justified. PIs should make sure that the source fits within the inner 1/3 of the primary beam (field of view), or alternatively discuss the effects of the sensitivity loss towards the beam edges. Finally, overriding the OT recommendation concerning the use of the ACA must be justified.
– Correlator setup: the requested correlator setup, including the total bandwidth, spectral resolution, and spectral window placement should be justified. Additional details of the correlator setup are automatically defined by the OT in Phase 2 (based on the Phase 1 request) and will not normally need to be adjusted. In rare instances though this might be necessary. Examples include requiring a smoothing function other than Hanning or a very short integration time. Such requirements should be justified.
– Calibration: By default, ALMA observations will contain observations of sources necessary to calibrate the flux scale, bandpass and the relative gains of each antenna. For a small fraction of projects, e.g. those requiring a high spectral dynamic range, it might be necessary to perform additional calibrations and/or to use specific sources. Requests for user-defined calibrators must be justified.
– Bandpass accuracy: Projects that intend to observe spectral features that cover a significant fraction of a spw, and/or study spectral features with small contrast with respect to a strong continuum are affected by the bandpass accuracy. It has been determined that, for Cycle 3, projects that require spectral response accuracies per observation execution of up to 1000 for ALMA Bands 3,4 and 6 and 500 for Bands 7, 8, 9 and 10 are feasible. Requests for higher accuracies may be the grounds for rejection of the proposal (see section A-9.3 of the Cycle 3 Proposer's Guide and Capabilities).
– Scheduling/time constraints: most ALMA projects are not time constrained i.e. they will be dynamically scheduled when the source is at sufficient altitude above the horizon and the atmospheric conditions are appropriate for the wavelength being observed. However, some projects may have time constraints. The OT currently has the ability to capture specific time intervals, multiple epochs as well as one or more monitoring visits. In the latter case, the OT's sensitivity-based time estimate is overridden by the combined length of the monitoring visits specified. Any time constraints requested must be justified.
– Data rate: the maximum data rate is 60 MB/s, with an expected average of 6 MB/s. Spectral setups that result in a data rate that is more than twice the expected average of 6 MB/s must be justified.
– Special constraints on standard observing modes: these include requests for observations whose overheads are very high (> 30% of the total requested time), very short observations (less than 2 minutes on-source time) and lengthy observations (continuous target observations for more than 40 minutes). If such requests are made, they must be justified.
Any non-standard choices regarding the technical setup of the Science Goal (including those specifically mentioned above) will be explicitly listed above the Technical Justification text box and must be carefully justified.