2025ApJ...992...18P

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Class 0 protostar IRAS 04166+2706, obtained as part of the ALMA Large Program Early Planet Formation in Embedded Disks. These observations were made in the 1.3 mm dust continuum and molecular lines at angular resolutions of $\sim 0\mathop{.}\limits{^{\prime\prime} }05$ (∼8 au) and $\sim 0\mathop{.}\limits{^{\prime\prime} }16$ (∼25 au), respectively. The continuum emission shows a disklike structure with a radius of ∼22 au. Kinematical analysis of ¹³CO (2-1), C¹⁸O (2-1), H₂CO (3_0,3-2_0,2), CH₃OH (4₂-3₁) emission demonstrates that these molecular lines trace the infalling-rotating envelope and possibly a Keplerian disk, enabling us to estimate the protostar mass to be 0.15 M_⊙ < M_⋆ < 0.39 M_⊙. The dusty disk is found to exhibit a brightness asymmetry along its minor axis in the continuum emission, probably caused by a flared distribution of the dust and the high optical depth of the dust emission. In addition, the ¹²CO (2-1) and SiO (5-4) emissions show knotty and wiggling motions in the jets. Our high-angular-resolution observations revealed the most recent mass ejection events, which have occurred within the last ∼25 yr.