Discovery of a collimated jet from the low luminosity protostar IRAS 16253$-$2429 in a quiescent accretion phase with the JWST

Abstract

Investigating Protostellar Accretion (IPA) is a JWST Cycle~1 GO program that uses NIRSpec IFU and MIRI MRS to obtain 2.9--28~$\hat{I}¼$m spectral cubes of young, deeply embedded protostars with luminosities of 0.2 to 10,000~L${}_{\odot }$ and central masses of 0.15 to 12~M${}_{\odot }$. In this Letter, we report the discovery of a highly collimated atomic jet from the Class~0 protostar IRAS~16253$-$2429, the lowest luminosity source ($L_{\mathrm{bol}}$ = 0.2 $L_{\odot }$) in the IPA program. The collimated jet is detected in multiple [Fe~II] lines, [Ne~II], [Ni~II], and H~I lines, but not in molecular emission. The atomic jet has a velocity of about 169~$\pm$~15~km\,s${}^{-1}$, after correcting for inclination. The width of the jet increases with distance from the central protostar from 23 to~60 au, corresponding to an opening angle of 2.6~$\pm$~0.5\arcdeg. By comparing the measured flux ratios of various fine structure lines to those predicted by simple shock models, we derive a shock {speed} of 54~km\,s${}^{-1}$ and a preshock density of 2.0$\times 10^3$~cm${}^{-3}$ at the base of the jet. {From these quantities and using a suite of jet models and extinction laws we compute a mass loss rate between $0.4-1.1\times 10^{-10}{M}_{\odot }$~yr~${}^{-1}$.} The low mass loss rate is consistent with simultaneous measurements of low mass accretion rate ($2.4\pm 0.8\times 10^{-9}{M}_{\odot }$~yr${}^{-1}$) for IRAS~16253$-$2429 from JWST observations (Watson et al. in prep), indicating that the protostar is in a quiescent accretion phase. Our results demonstrate that very low-mass protostars can drive highly collimated, atomic jets, even during the quiescent phase.

Accepted to ApJL. Comments and feedback welcome