Probing the Upper Scorpius mass function in the planetary-mass regime★

The σ Orionis cluster (~3 Myr, 350 pc) is an ideal site to investigate the early evolution of substellar (brown dwarf and planetary mass) objects. To date, the cluster photometric and spectroscopic sequence of free-floaters is known for a wide mass range from 1 M⊙ down to roughly 3 MJup. The substellar domain covers spectral types that go from mid-M classes to the recently defined “methane” T-types, i.e., surface temperatures between ~3000K and 800 K. We derive a rising initial substellar mass function in the mass interval of 150–5 MJup (dN/dM ~ M-α, with α = 0.9 ± 0.4). We also find evidence for a extension of this mass function toward lower masses down to 2–3 MJup. This indicates that the population of isolated planetary mass objects with masses below the deuterium burning threshold is rather abundant in the cluster.

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System initial mass function of the 25 Ori group from planetary-mass objects to intermediate/high-mass stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz756 ◽

2019 ◽

Vol 486 (2) ◽

pp. 1718-1740 ◽

Cited By ~ 4

Author(s):

Genaro Suárez ◽

Juan José Downes ◽

Carlos Román-Zúñiga ◽

Miguel Cerviño ◽

César Briceño ◽

...

Keyword(s):

Power Law ◽

Near Infrared ◽

Mass Range ◽

Mass Function ◽

Initial Mass Function ◽

High Mass ◽

Initial Mass ◽

Formation Mechanisms ◽

Stellar Association ◽

Planetary Mass

Abstract The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases has it been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory for investigating the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1° radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 M⊙. This system IMF is well described by a two-segment power law with Γ = −0.74 ± 0.04 for m < 0.4 M⊙ and Γ = 1.50 ± 0.11 for m ≥ 0.4 M⊙. It is also well described over the whole mass range by a tapered power-law function with Γ = 1.10 ± 0.09, mp = 0.31 ± 0.03 and β = 2.11 ± 0.09. The best lognormal representation of the system IMF has mc = 0.31 ± 0.04 and σ = 0.46 ± 0.05 for m < 1 M⊙. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the brown dwarf/star ratio of 0.16 ± 0.03 that we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star-formation mechanisms are probably not strongly dependent on environmental conditions. We found that the substellar and stellar objects in 25 Ori do not have any preferential spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.

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Zeldovich and the Missing Baryons, Results from Gravitational Lensing

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316010218 ◽

2014 ◽

Vol 11 (S308) ◽

pp. 380-381

Author(s):

Rudolph E. Schild

Keyword(s):

Dark Matter ◽

Distribution Function ◽

Gravitational Lensing ◽

Mass Function ◽

Gravitational Theory ◽

Magellanic Clouds ◽

Planetary Mass ◽

Mass Distribution Function ◽

Baryonic Dark Matter

AbstractCentral to Zeldovich's attempts to understand the origin of cosmological structure was his exploration of the fluid dynamical effects in the primordial gas, and how the baryonic dark matter formed. Unfortunately microlensing searches for condensed objects in the foreground of the Magellanic Clouds were flawed by the assumption that the objects would be uniformly (Gaussian) distributed, and because the cadence of daily observations strongly disfavored detection of planet mass microlenses. But quasar microlensing showed them to exist at planetary mass at the same time that a hydro-gravitational theory predicted the planet-mass population as fossils of turbulence at the time of recombination (z = 1100; Gibson 1996, 2001). Where the population has now been detected from MACHO searches to the LMC (Sumi et al. 2011) we compare the quasar microlensing results to the recent determination of the mass distribution function measured for the planetary mass function, and show that the population can account for the baryonic dark matter.

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