The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU

Abstract

We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey (GPIES). 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, semi-major axis, and host stellar mass. We uncover a strong correlation between planet occurrence rate and host star mass, with stars M $>$ 1.5 $M_{\odot }$ more likely to host planets with masses between 2-13 M${}_{\mathrm{Jup}}$ and semi-major axes of 3-100 au at 99.92% confidence. We fit a double power-law model in planet mass (m) and semi-major axis (a) for planet populations around high-mass stars (M $>$ 1.5M${}_{\odot }$) of the form $\frac{d^{2}N}{dmda}\propto m^{\hat{I}}\pm a^2$, finding $\hat{I}\pm$ = -2.4 $\pm$ 0.8 and ${\hat{I}}^2$ = -2.0 $\pm$ 0.5, and an integrated occurrence rate of $9_{-4}^{+5}$% between 5-13 M${}_{\mathrm{Jup}}$ and 10-100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with 0.8${}_{-0.5}^{+0.8}$% of stars hosting a brown dwarf companion between 13-80 M${}_{\mathrm{Jup}}$ and 10-100 au. Brown dwarfs also appear to be distributed differently in mass and semi-major axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semi-major axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of short-period giant planets from the RV method, our results are consistent with a peak in occurrence of giant planets between ~1-10 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.

52 pages, 18 figures. AJ in press