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Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. II. Free-floating Planet Detection Rates

Johnson, Samson A. and Penny, Matthew and Gaudi, B. Scott and Kerins, Eamonn and Rattenbury, Nicholas J. and Robin, Annie C. and Calchi Novati, Sebastiano and Henderson, Calen B. (2020) Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. II. Free-floating Planet Detection Rates. Astronomical Journal, 160 (3). Art. No. 123. ISSN 1538-3881. doi:10.3847/1538-3881/aba75b.

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The Nancy Grace Roman Space Telescope (Roman) will perform a Galactic Exoplanet Survey (RGES) to discover bound exoplanets with semimajor axes greater than 1 au using gravitational microlensing. Roman will even be sensitive to planetary-mass objects that are not gravitationally bound to any host star. Such free-floating planetary-mass objects (FFPs) will be detected as isolated microlensing events with timescales shorter than a few days. A measurement of the abundance and mass function of FFPs is a powerful diagnostic of the formation and evolution of planetary systems, as well as the physics of the formation of isolated objects via direct collapse. We show that Roman will be sensitive to FFP lenses that have masses from that of Mars (0.1 M⊕) to gas giants (M ≳ 100 M⊕) as isolated lensing events with timescales from a few hours to several tens of days, respectively. We investigate the impact of the detection criteria on the survey, especially in the presence of finite-source effects for low-mass lenses. The number of detections will depend on the abundance of such FFPs as a function of mass, which is at present poorly constrained. Assuming that FFPs follow the fiducial mass function of cold, bound planets adapted from Cassan et al., we estimate that Roman will detect ~250 FFPs with masses down to that of Mars (including ~60 with masses ≤ M⊕). We also predict that Roman will improve the upper limits on FFP populations by at least an order of magnitude compared to currently existing constraints.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Johnson, Samson A.0000-0001-9397-4768
Penny, Matthew0000-0001-7506-5640
Gaudi, B. Scott0000-0003-0395-9869
Kerins, Eamonn0000-0002-1743-4468
Rattenbury, Nicholas J.0000-0001-5069-319X
Robin, Annie C.0000-0001-8654-9499
Calchi Novati, Sebastiano0000-0002-7669-1069
Henderson, Calen B.0000-0001-8877-9060
Additional Information:© 2020 The American Astronomical Society. Received 2020 June 23; revised 2020 July 15; accepted 2020 July 16; published 2020 August 21. During the preparation of this manuscript, the name of the Wide Field Infrared Survey Telescope was changed to the Nancy Grace Roman Space Telescope. We appreciate the revisions from the referee that improved the quality of this work, as well as those from careful readings by Radek Poleski and Przemek Mróz. We thank our colleagues Andrew Gould and David Bennett for useful discussions. We thank everyone on the Roman Galactic Exoplanet Survey Science Investigation Team. We also appreciate Exoplanet Lunch at Ohio State University, which was the source of many useful discussions. S.A.J. dedicates his contribution to this work to David John Prahl Will, without whom this work and that of many others would not be possible. This work was performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. S.A.J., M.T.P., and B.S.G. were supported by NASA grant NNG16PJ32C and the Thomas Jefferson Chair for Discovery and Space Exploration. Software: astropy (Astropy Collaboration et al. 2013, 2018), Matplotlib (Hunter 2007), MulensModel (Poleski & Yee 2018), VBBinaryLensing (Bozza 2010; Bozza et al. 2018).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Thomas Jefferson Chair for Discovery and Space ExplorationUNSPECIFIED
Subject Keywords:Gravitational microlensing ; Free floating planets ; Space telescopes ; Exoplanet detection methods
Issue or Number:3
Classification Code:Unified Astronomy Thesaurus concepts: Gravitational microlensing (672); Free floating planets (549); Space telescopes (1547); Exoplanet detection methods (489)
Record Number:CaltechAUTHORS:20200824-071328207
Persistent URL:
Official Citation:Samson A. Johnson et al 2020 AJ 160 123
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105064
Deposited By: Tony Diaz
Deposited On:24 Aug 2020 16:22
Last Modified:16 Nov 2021 18:39

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