Observational constraints on the connection between hot exozodiacal dust and outer planetesimal belts

Hot exozodiacal dust has been identified to be present in the innermost regions of an increasing number of main sequence stars over the past decade. The origin of this dust and its connection with outer dust reservoirs remain however unclear. In this talk, we report on the latest results from near-infrared interferometric observations. We particularly focus on a new survey of about 50 stars with VLTI/PIONIER aimed to explore the possible connection between hot exozodiacal dust and warm dust reservoirs in asteroid belts. This survey reveals the presence of hot dust around 13 new stars, which add to the 9 detections already reported with the same instrument by Ertel et al. in 2014. After reassessing the warm dust content of all our PIONIER targets through spectral energy distribution modeling, we find a detection rate of 17.1(+8.1)(-4.6)% for H-band excess around main sequence stars hosting warm dust belts (> 100 K), which is statistically compatible with the occurrence rate of 14.6(+4.3)(-2.8)% found around stars showing no signs of warm dust. After correcting for the sensitivity loss due to partly unresolved hot disks, under the assumption that they are arranged in a thin ring around their sublimation radius, we however find tentative evidence at the 3σ level that H-band excesses around stars with outer dust reservoirs (warm or cold) is statistically larger than H-band excesses around stars with no detectable outer dust. While our observations do not suggest a direct connection between warm and hot dust populations, they bring to light a possible correlation between the level of H-band excesses and the presence of outer dust reservoirs in general. We discuss the implications of these new results on our understanding of the nature and origin of near-infrared excesses around main sequence stars. We conclude this talk by discussing the prospects for improving this understanding using the latest and upcoming interferometric instruments, such as GRAVITY, MATISSE, and Hi-5.