A Search for Wide-orbit Planets Around M-dwarfs using Deep MIRI 15-micron Images

Abstract: Wide-orbit ($>$10 AU) gas giant planets shape the architecture of planetary systems, yet their occurrence rate remains poorly constrained. JWST has obtained the deepest mid-infrared images of nearby stars to date through substantial MIRI time-series observations of transiting planets, providing sensitive probes for wide-orbit companions. Here we leverage 15 micron observations from four programs targeting ten M-dwarf systems to search for such planets. By applying reference differential imaging for precise PSF subtraction, we achieve a median 5$σ$ contrast of $8.9 \times 10^{-4} - 6.2 \times 10^{-3}$ (median sensitivity in apparent magnitude of 15.8-16.8 mag) at a separation of 1" and $1.2 -9.1 \times 10^{-4}$ (17.5-19.0 mag) at separations $\gtrsim$3". The sensitivity is converted to planet detection probability for each system as a function of planet mass versus semimajor axis. Assuming solar metallicity and a clear atmosphere, we are sensitive to Jupiter-sized planets with an effective temperature of ${\sim}170$ K at separations beyond 35 AU in systems at 12.5 pc. Additionally, we catalog the nearby sources and estimate their possible impact on future observations assuming they are background sources. Our results demonstrate that archival MIRI time-series imaging data is a powerful window into the population of wide-orbit gas giants around M-dwarfs.