The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au

Abstract

We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey. This subsample includes six detected planets and three brown dwarfs; from these detections and our contrast curves we infer the underlying distributions of substellar companions with respect to their mass, semimajor axis, and host stellar mass. We uncover a strong correlation between planet occurrence rate and host star mass, with stars M-* > 1.5 M-circle dot more likely to host planets with masses between 2 and 13M(Jup) and semimajor axes of 3-100 au at 99.92% confidence. We fit a double power-law model in planet mass (m) and semimajor axis (a) for planet populations around high-mass stars (M-* > 1.5 M-circle dot) of the form d(2)N/(dm da) proportional to m(alpha) a(beta), finding alpha = -2.4 +/- 0.8 and beta = -2.0 +/- 0.5, and an integrated occurrence rate of 9(-4)(+5)% between 5-13M(Jup )and 10-100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with 0.81(-0.5)(+0.8)% of stars hosting a brown dwarf companion between 13-80M(Jup) and 10-100 au. Brown dwarfs also appear to be distributed differently in mass and semimajor axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semimajor axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of shortperiod giant planets from the radial velocity method, our results are consistent with a peak in occurrence of giant planets between similar to 1 and 10 au. We discuss how these trends, including the preference of giant planets for high-mass host stars, point to formation of giant planets by core/pebble accretion, and formation of brown dwarfs by gravitational instability.