Giga-z: A 100,000 Object Superconducting Spectrophotometer for LSST Follow-up

Abstract

We simulate the performance of a new type of instrument, a Superconducting Multi-Object Spectrograph (SuperMOS), that uses microwave kinetic inductance detectors (MKIDs). MKIDs, a new detector technology, feature good quantum efficiency in the UVOIR, can count individual photons with microsecond timing accuracy, and, like X-ray calorimeters, determine their energy to several percent. The performance of Giga-z, a SuperMOS designed for wide field imaging follow-up observations, is evaluated using simulated observations of the COSMOS mock catalog with an array of 100,000 R_(423 nm) = E/ΔE = 30 MKID pixels. We compare our results against a simultaneous simulation of LSST observations. In 3 yr on a dedicated 4 m class telescope, Giga-z could observe ≈2 billion galaxies, yielding a low-resolution spectral energy distribution spanning 350–1350 nm for each; 1000 times the number measured with any currently proposed LSST spectroscopic follow-up, at a fraction of the cost and time. Giga-z would provide redshifts for galaxies up to z ≈ 6 with magnitudes m_i ≾ 25, with accuracy σ_(Δz/(1 + z)) ≈ 0.03 for the whole sample, and σ_(Δz/(1 + z)) ≈ 0.007 for a select subset. We also find catastrophic failure rates and biases that are consistently lower than for LSST. The added constraint on dark energy parameters for WL + CMB by Giga-z using the FoMSWG default model is equivalent to multiplying the LSST Fisher matrix by a factor of α = 1.27 (w_p), 1.53 (w_a), or 1.98 (Δγ). This is equivalent to multiplying both the LSST coverage area and the training sets by α and reducing all systematics by a factor of 1/√ α, advantages that are robust to even more extreme models of intrinsic alignment.