HST survey of the Orion Nebula Cluster in the H${}_2$O 1.4 $\mu$m absorption band: II. The substellar IMF down to planetary masses

Abstract

We exploit the ability of the Hubble Space Telescope to probe near infrared water absorption present in the atmosphere of low-mass stars, brown dwarfs and planetary mass objects to create a very pure sample of Orion Nebula Cluster (ONC) members, not affected by contamination from background stars and galaxies which lack water absorption. Thanks to these data we infer the Initial Mass Function (IMF) of the ONC in the $0.005-1.4$M${}_{\odot }$ regime, i.e. down to few Jupiter masses. The young age of the ONC, $\sim 1$ Myr, provides a snapshot of the outcome of star formation for the present-day conditions (metallicity, temperature, pressure) of typical Milky Way disk molecular clouds. We demonstrate that the IMF of the ONC is well described by either a log-normal function or a broken power-law, with parameter values qualitatively in agreement with the canonical Chabrier or Kroupa forms for the Milky Way disk IMF. This continuity in the mass distribution provides clues to the fact that the same physical processes may be regulating formation of stars, brown dwarfs, and planetary mass objects. Both the canonical IMF forms under-predict the observed number of very low mass members (below $0.1$ M${}_{\odot }$), a regime where our data allows more precise constraints. Nevertheless, we do not observe a rise or secondary peak in the brown dwarfs or planetary mass regimes. Our study thus contradicts findings based on broad-band near infrared ground-based photometry, which predict an extremely high number of free-floating planets, but likely suffer from unaccounted background contamination.

Accepted for publication in the Astrophysical Journal

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Cited by in corpus (8)

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• HST survey of the Orion Nebula Cluster in the H${}_2$O 1.4 $\mu$m absorption band: I. A census of substellar and planetary mass objects
• A novel survey for young substellar objects with the W-band filter VI: Spectroscopic census of sub-stellar members and the IMF of $\sigma$ Orionis cluster
• The TEMPO Survey I: Predicting Yields of the Transiting Exosatellites, Moons, and Planets from a 30-day Survey of Orion with the Nancy Grace Roman Space Telescope
• Identification of a turnover in the initial mass function of a young stellar cluster down to 0.5 M${}_J$
• Spectroscopic substellar initial mass function of NGC 2244
• An APEX search for carbon emission from NGC 1977 proplyds
• HST survey of the Orion Nebula Cluster in the H${}_2$O 1.4 $\mu$m absorption band: III. The population of sub-stellar binary companions