2016ApJ...824...58D

We report results of a re-analysis of archival Spitzer IRAC direct imaging surveys encompassing a variety of nearby stars. Our sample is generated from the combined observations of 73 young stars (median age, distance, spectral type=85 Myr, 23.3 pc, G5) and 48 known exoplanet host stars with unconstrained ages (median distance, spectral type=22.6 pc, G5). While the small size of Spitzer provides a lower resolution than 8 m class AO-assisted ground-based telescopes, which have been used for constraining the frequency of 0.5-13 M_ J_ planets at separations of 10-10² au, its exquisite infrared sensitivity provides the ability to place unmatched constraints on the planetary populations at wider separations. Here we apply sophisticated high-contrast techniques to our sample in order to remove the stellar point-spread function and to open up sensitivity to planetary mass companions down to 5'' separations. This enables sensitivity to 0.5-13 M_ J_ planets at physical separations on the order of 10²-10³ au, allowing us to probe a parameter space that has not previously been systematically explored to any similar degree of sensitivity. Based on a color and proper motion analysis, we do not record any planetary detections. Exploiting this enhanced survey sensitivity, employing Monte Carlo simulations with a Bayesian approach, and assuming a mass distribution of {dn}/{dm}∝{m}^{-1.31} , we constrain (at 95% confidence) a population of 0.5-13 M_ J_ planets at separations of 100-1000 au with an upper frequency limit of 9%.