Friends not Foes: Strong Correlation between Inner Super-Earths and Outer Gas Giants

Marta L. Bryan, Eve J. Lee

Published 2024-03-13Version 1

The connection between outer gas giants and inner super-Earths reflects their formation and evolutionary histories. Past work exploring this link has suggested a tentative positive correlation between these two populations, but these studies have been limited by small sample sizes and in some cases sample biases. Here we take a new look at this connection with a sample of 184 super-Earth systems with publicly available radial velocity data and fully resolved outer gas giants. We calculate the frequency of outer gas giants (GG) in super-Earth (SE) systems, dividing our sample into metal-rich ([Fe/H] $>$ 0) and metal-poor ([Fe/H]$\leq$0) hosts. We find P(GG$|$SE, [Fe/H]$>$0) = 28.0$^{+4.9}_{-4.6}\%$ and P(GG$|$SE, [Fe/H]$\leq$0) = 4.5$^{+2.6}_{-1.9}\%$. Comparing these conditional occurrence rates to field giant occurrence rates from Wittenmyer et al. 2020, we show that there is a distinct positive correlation between inner super-Earths and outer gas giants for metal-rich host stars at the 2.5$\sigma$ level, but this correlation disappears for metal-poor systems. We further find that, around metal-rich stars, the GG/SE correlation enhances for systems with giants that are more distant (beyond 3 AU) and/or more eccentric ($e > 0.2$), while gas giant multiplicity does not appear to affect the level of correlation. Such trends again disappear around metal-poor stars with the exception of systems of multiple giants in which we observe an anti-correlation. Our findings highlight the critical role metallicity (disk solid budget) plays in shaping the overall planetary architecture.