Extremely Dense Cores associated with Chandra Sources in Ophiuchus A: Forming Brown Dwarfs Unveiled?

TL;DR

This study identifies two extremely young protostellar objects in Ophiuchus A that are likely proto-brown dwarfs or in the earliest stages of star formation, characterized by FHSC-like properties, faint IR signatures, X-ray activity, and outflows.

Contribution

The paper provides observational evidence for proto-brown dwarfs in early formation stages, linking multi-wavelength data to theoretical models of first hydrostatic cores.

Findings

Confirmed two bona fide proto-BDs in early evolutionary stages.

Detected faint X-ray sources associated with the objects.

Observed CO outflows indicating active mass ejection.

Abstract

On the basis of various data such as ALMA, JVLA, Chandra, {\it Herschel}, and {\it Spitzer}, we confirmed that two protostellar candidates in Oph-A are bona fide protostars or proto-brown dwarfs (proto-BDs) in extremely early evolutionary stages. Both objects are barely visible across infrared (IR, i.e., near-IR to far-IR) bands. The physical nature of the cores is very similar to that expected in first hydrostatic cores (FHSCs), objects theoretically predicted in the evolutionary phase prior to stellar core formation with gas densities of $\sim$ 10$^{11-12}$ cm$^{-3}$. This suggests that the evolutionary stage is close to the FHSC formation phase. The two objects are associated with faint X-ray sources, suggesting that they are in very early phase of stellar core formation with magnetic activity. In addition, we found the CO outflow components around both sources which may originate from the young outflows driven by these sources. The masses of these objects are calculated to be $\sim 0.01-0.03$ $M_\odot$ from the dust continuum emission. Their physical properties are consistent with that expected from the numerical model of forming brown dwarfs. These facts (the X-ray detection, CO outflow association, and FHSC-like spectral energy distributions) strongly indicate that the two objects are proto-BDs or will be in the very early phase of protostars which will evolve more massive protostars if they gain enough mass from the surroundings. The ages of these two objects are likely to be within $\sim 10^3$ years after the protostellar core (or second core) formation, taking into account the outflow dynamical times ($\lesssim$ 500 yrs).