Dusty disks at the bottom of the IMF

TL;DR

This study investigates the presence of dusty disks around planetary-mass objects near the bottom of the initial mass function, revealing that many such objects retain disks for several million years, similar to stars and brown dwarfs.

Contribution

First survey to detect dusty disks around planetary-mass objects in the Sigma Orionis cluster using Spitzer data, showing disk presence at the lowest masses.

Findings

29% of IPMOs have disks at 8.0μm, similar to stars and brown dwarfs.

Detected IR excess in SOri70, indicating youth and very low mass.

Disks around IPMOs suggest formation via core collapse and fragmentation.

Abstract

'Isolated planetary mass objects' (IPMOs) have masses close to or below the Deuterium-burning mass limit (~15 Jupiter masses) -- at the bottom of the stellar initial mass function. We present an exploratory survey for disks in this mass regime, based on a dedicated observing campaign with the Spitzer Space Telescope. Our targets include the full sample of spectroscopically confirmed IPMOs in the Sigma Orionis cluster, a total of 18 sources. In the mass range 8... 20 MJup, we identify 4 objects with >3sigma colour excess at a wavelength of 8.0mu, interpreted as emission from dusty disks. We thus establish that a substantial fraction of IPMOs harbour disks with lifetimes of at least 2-4 Myr (the likely age of the cluster), indicating an origin from core collapse and fragmentation processes. The disk frequency in the IPMO sample is 29% (16-45%) at 8.0mu, very similar to what has been found for stars and brown dwarfs (~30%). The object SOri70, a candidate 3 MJup object in this cluster, shows IRAC colours in excess of the typical values for field T dwarfs (on a 2sigma level), possibly due to disk emission or low gravity. This is a new indication for youth and thus an extremely low mass for SOri70.