The Astronomical Journal (Jan 2023)
Free-floating Planet Mass Function from MOA-II 9 yr Survey toward the Galactic Bulge
- Takahiro Sumi,
- Naoki Koshimoto,
- David P. Bennett,
- Nicholas J. Rattenbury,
- Fumio Abe,
- Richard Barry,
- Aparna Bhattacharya,
- Ian A. Bond,
- Hirosane Fujii,
- Akihiko Fukui,
- Ryusei Hamada,
- Yuki Hirao,
- Stela Ishitani Silva,
- Yoshitaka Itow,
- Rintaro Kirikawa,
- Iona Kondo,
- Yutaka Matsubara,
- Shota Miyazaki,
- Yasushi Muraki,
- Greg Olmschenk,
- Clément Ranc,
- Yuki Satoh,
- Daisuke Suzuki,
- Mio Tomoyoshi,
- Paul . J. Tristram,
- Aikaterini Vandorou,
- Hibiki Yama,
- Kansuke Yamashita,
- MOA Collaboration
Affiliations
- Takahiro Sumi
- ORCiD
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Naoki Koshimoto
- ORCiD
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]; Code 667, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA; Department of Astronomy, University of Maryland , College Park, MD 20742, USA
- David P. Bennett
- ORCiD
- Code 667, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA; Department of Astronomy, University of Maryland , College Park, MD 20742, USA
- Nicholas J. Rattenbury
- ORCiD
- Department of Physics, University of Auckland , Private Bag 92019, Auckland, New Zealand
- Fumio Abe
- Institute for Space-Earth Environmental Research, Nagoya University , Nagoya 464-8601, Japan
- Richard Barry
- ORCiD
- Code 667, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA
- Aparna Bhattacharya
- Code 667, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA; Department of Astronomy, University of Maryland , College Park, MD 20742, USA
- Ian A. Bond
- Institute of Natural and Mathematical Sciences, Massey University , Auckland 0745, New Zealand
- Hirosane Fujii
- Institute for Space-Earth Environmental Research, Nagoya University , Nagoya 464-8601, Japan
- Akihiko Fukui
- ORCiD
- Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Instituto de Astrofísica de Canarias , Vía Láctea s/n, E-38205 La Laguna, Tenerife, Spain
- Ryusei Hamada
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Yuki Hirao
- ORCiD
- Institute of Astronomy, Graduate School of Science, The University of Tokyo , 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
- Stela Ishitani Silva
- Code 667, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA; Department of Physics, The Catholic University of America , Washington, DC 20064, USA
- Yoshitaka Itow
- ORCiD
- Institute for Space-Earth Environmental Research, Nagoya University , Nagoya 464-8601, Japan
- Rintaro Kirikawa
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Iona Kondo
- ORCiD
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Yutaka Matsubara
- ORCiD
- Institute for Space-Earth Environmental Research, Nagoya University , Nagoya 464-8601, Japan
- Shota Miyazaki
- ORCiD
- Institute of Space and Astronautical Science , Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan
- Yasushi Muraki
- ORCiD
- Institute for Space-Earth Environmental Research, Nagoya University , Nagoya 464-8601, Japan
- Greg Olmschenk
- ORCiD
- Code 667, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA
- Clément Ranc
- ORCiD
- Sorbonne Université , CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, F-75014 Paris, France
- Yuki Satoh
- ORCiD
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Daisuke Suzuki
- ORCiD
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Mio Tomoyoshi
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Paul . J. Tristram
- University of Canterbury Mt. John Observatory , P.O. Box 56, Lake Tekapo 8770, New Zealand
- Aikaterini Vandorou
- Code 667, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA; Department of Astronomy, University of Maryland , College Park, MD 20742, USA
- Hibiki Yama
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- Kansuke Yamashita
- Department of Earth and Space Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan ; [email protected]
- MOA Collaboration
- DOI
- https://doi.org/10.3847/1538-3881/ace688
- Journal volume & issue
-
Vol. 166,
no. 3
p. 108
Abstract
We present the first measurement of the mass function of free-floating planets (FFPs), or very wide orbit planets down to an Earth mass, from the MOA-II microlensing survey in 2006–2014. Six events are likely to be due to planets with Einstein radius crossing times t _E < 0.5 days, and the shortest has t _E = 0.057 ± 0.016 days and an angular Einstein radius of θ _E = 0.90 ± 0.14 μ as. We measure the detection efficiency depending on both t _E and θ _E with image-level simulations for the first time. These short events are well modeled by a power-law mass function, ${{dN}}_{4}/d\mathrm{log}M={({2.18}_{-1.40}^{+0.52})\times (M/8\,{M}_{\oplus })}^{-{\alpha }_{4}}$ dex ^−1 star ^−1 with ${\alpha }_{4}={0.96}_{-0.27}^{+0.47}$ for M / M _⊙ < 0.02. This implies a total of $f={21}_{-13}^{+23}$ FFPs or very wide orbit planets of mass 0.33 < M / M _⊕ < 6660 per star, with a total mass of ${80}_{-47}^{+73}{M}_{\oplus }$ star ^−1 . The number of FFPs is ${19}_{-13}^{+23}$ times the number of planets in wide orbits (beyond the snow line), while the total masses are of the same order. This suggests that the FFPs have been ejected from bound planetary systems that may have had an initial mass function with a power-law index of α ∼ 0.9, which would imply a total mass of ${171}_{-52}^{+80}{M}_{\oplus }$ star ^−1 . This model predicts that Roman Space Telescope will detect ${988}_{-566}^{+1848}$ FFPs with masses down to that of Mars (including ${575}_{-424}^{+1733}$ with 0.1 ≤ M / M _⊕ ≤ 1). The Sumi et al. large Jupiter-mass FFP population is excluded.
Keywords
- Gravitational microlensing
- Gravitational microlensing exoplanet detection
- Free floating planets
- Exoplanet astronomy
- Galactic bulge
