Investigating the Nested Structure of the Outflow from the Low Luminosity Protostar IRAS 16253-2429 using JWST and ALMA

Abstract: Understanding the earliest stage of star and planet formation requires detailed observations to address the connection and interplay between the accretion, outflow, and disk evolution. We present results from observations of the low luminosity ($L_{\mathrm{bol}} \sim 0.2,L_{\odot}$) and low mass ($M_{*} \sim 0.15,M_{\odot}$) Class 0 protostar IRAS~16253$-$2429, conducted as part of the eDisk ALMA Large Program and the JWST Cycle~1 GO program IPA. Observations reveal a wide hourglass-shaped continuum cavity traced in scattered light (at $\leq 5,μ$m), with a brighter, extended northern side. We detect 15 pure rotational H$2$ transitions ($E{\mathrm{up}} = 1015$--21411~K), revealing a wide-angle molecular outflow. The outflow width traced by H$_2$~0-0~S(11) at the protostellar location measures $\leq 35$~au, slightly larger than the dust and Keplerian disk diameters ($\sim 30$~au) but wider than the 20--23~au jet width in [Fe~II]. The opening angle narrows from 40--35 degrees for the low-$J$ H$_2$ lines (up to S(5)) and the cold gas component traced by ALMA $<sup>{12}$CO to $\sim 28$--19 degrees for the high-$J$ H$_2$ lines (S(7)--S(11)). Position--velocity diagrams of H$2$ reveal higher velocities for higher $E{\mathrm{up}}$, ranging from $\sim 12.5$~km~s$<sup>{-1}$ for H$_2$~0-0~S(1) and S(2) to $\sim 28.5$~km~s$<sup>{-1}$ for H$_2$~0-0~S(5) and S(7) with respect to the mean flow velocity. The nested excitation and velocity structure of the collimated jet and wide-angle wind suggests a magnetohydrodynamic wind as a likely launching mechanism, similar to findings in other protostars and Class~II sources. The lower-velocity millimeter CO emission may be gas from the infalling envelope accelerated outward by the wide-angle wind along the cavity walls.