Target allocation yields for massively multiplexed spectroscopic surveys with fibers
2014
We present Simulated Annealing fiber-to-target allocation simulations for the proposed
DESIand 4MOST massively multiplexed spectroscopic surveys, and for both Poisson and realistically clustered mock target samples. We simulate both
Echidnaand theta-phi actuator designs, including the restrictions caused by the physical actuator characteristics during repositioning. For
DESI, with theta-phi actuators, used in 5 passes over the sky for a mock ELG/LRG/
QSOsample, with matched fiber and target densities, a total target allocation yield of 89.3% was achieved, but only 83.7% for the high-priority Ly-alpha
QSOs. If
Echidnaactuators are used with the same pitch and number of passes, the yield increases by 5.7% and 16% respectively.
Echidnaalso allows a factor-of-two increase in the number of close Ly-alpha
QSOpairs that can be observed.
Echidnaspine tilt causes a variable loss of throughput, with average loss being the same as the loss at the rms tilt. With a natural tilt minimization scheme, we find an rms tilt always close to 0.58 x maximum. There is an additional but much smaller defocus loss, equivalent to an average defocus of 30microns. These tilt losses offset the gains in yield for
Echidna, but because the survey strategy is driven by the higher priority targets, a clear survey speed advantage remains. For 4MOST, high and low latitude sample mock catalogs were supplied by the 4MOST team, and allocations were carried out with the proposed
Echidna-based positioner geometry. At high latitudes, the resulting target completeness was 85.3% for LR targets and 78.9% for HR targets. At low latitude, the target completeness was 93.9% for LR targets and 71.2% for HR targets.
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