The Atacama Cosmology Telescope: A search for Planet 9
Sigurd Naess, Simone Aiola, Nick Battaglia, Richard J. Bond, Erminia, Calabrese, Steve K. Choi, Nicholas F. Cothard, Mark Halpern, J. Colin Hill,, Brian J. Koopman, Mark Devlin, Jeff McMahon, Simon Dicker, Adriaan J., Duivenvoorden, Jo Dunkley, Alexander Van Engelen

TL;DR
This study uses Atacama Cosmology Telescope data to search for Planet 9 within 300-2000 AU, setting new limits on its possible brightness and excluding significant parameter space where it could exist.
Contribution
First blind mm-wave search for Planet 9 using ACT data, providing new constraints on its flux density and orbital parameters.
Findings
No significant detection of Planet 9.
Eliminated 17% of parameter space for 5 Earth-mass Planet 9.
Excluded bright unknown objects within certain distances and velocities.
Abstract
We use Atacama Cosmology Telescope (ACT) observations at 98 GHz (2015--2019), 150 GHz (2013--2019) and 229 GHz (2017--2019) to perform a blind shift-and-stack search for Planet 9. The search explores distances from 300 AU to 2000 AU and velocities up to 6.3 arcmin per year, depending on the distance. For a 5 Earth-mass Planet 9 the detection limit varies from 325 AU to 625 AU, depending on the sky location. For a 10 Earth-mass planet the corresponding range is 425 AU to 775 AU. The search covers the whole 18,000 square degrees of the ACT survey, though a slightly deeper search is performed for the parts of the sky consistent with Planet 9's expected orbital inclination. No significant detections are found, which is used to place limits on the mm-wave flux density of Planet 9 over much of its orbit. Overall we eliminate roughly 17% and 9% of the parameter space for a 5 and 10 Earth-mass…
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