Astronomy and Astrophysics
Aims: We aim to investigate the presence of debris disks around two of the closest (~20 pc), young substellar companions, namely G196-3 B and VHS J125601.92-125723.9 b (VHS J1256-1257 b), whose masses straddle the borderline between planets and brown dwarfs. Both are companions at wide orbits (≥100 au) of M-type dwarfs and their ages (50-100 Myr and 150-300 Myr, respectively) are thought to be adequate for the detection of second-generation disks.
Methods: We obtained deep images of G196-3 B and VHS J1256-1257 b with the NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm. These data were combined with recently published Atacama Large Millimeter Array (ALMA) and Very Large Array (VLA) data of VHS J1256-1257 b at 0.87 mm and 0.9 cm, respectively.
Results: Neither G196-3 B nor VHS J1256-1257 b were detected in the NOEMA, ALMA, and VLA data. At 1.3 mm, we imposed flux upper limits of 0.108 mJy (G196-3 B) and 0.153 mJy (VHS J1256-1257 b) with a 3-σ confidence. Using the flux upper limits at the millimeter and radio wavelength regimes, we derived maximum values of 1.38×10−2 MEarth and 5.46 × 10−3 MEarth for the mass of any cold dust that might be surrounding G196-3 B and VHS J1256-1257 b, respectively.
Conclusions: We put our results in the context of other deep millimeter observations of free-floating and companion objects with substellar masses smaller than 20 MJup and ages between approximately one and a few hundred million years. Only two very young (2-5.4 Myr) objects are detected out of a few tens of them. This implies that the disks around these very low-mass objects must have small masses, and possibly reduced sizes, in agreement with findings by other groups. If debris disks around substellar objects scale down (in mass and size) in a similar manner as protoplanetary disks do, millimeter observations of moderately young brown dwarfs and planets must be at least two orders of magnitude deeper to be able to detect and characterize their surrounding debris disks.