Probing the Low-Mass End of the Initial Mass Function with an HST DASH Survey of Star-Forming Regions

As the lowest-mass objects created by star formation processes, brown dwarfs are essential to a complete understanding of star formation in our galaxy. Leading models of the Initial Mass Function (IMF) differ most dramatically at the extreme low-mass tail, making brown dwarfs and free-floating planets the most sensitive test population for identifying the IMF's shape and possible variations. However, the low-mass IMF remains poorly constrained due to meager samples of these faint objects in the Solar neighborhood and nearby, relatively small star-forming regions. We are using deep HST drift-and-shift (DASH) images of five large benchmark Milky Way star-forming regions beyond the Solar neighborhood to comprehensively identify members down to planetary masses and explore variations of the IMF with star-forming environment. We are leveraging 1.4 micron water band photometry to distinguish reddened field interlopers from low-temperature cluster members and quantify interstellar extinction, an approach that is difficult to replicate from the ground. We present initial results from our survey, including a method to calibrate the relative contributions of extinction and water absorption using foreground stars identified by Gaia parallaxes.