CORINOS. III. Outflow Shocked Regions of the Low-mass Protostellar Source IRAS 15398–3359 with JWST and ALMA

Abstract While molecular outflows have been studied in detail with radio interferometry, observations of the hotter gas in protostellar outflows at a comparable physical scale are often challenging. Combined with the Atacama Large Millimeter/submillimeter Array (ALMA), JWST allows us to investigate the cold and hot gas with unprecedented spatial resolution and sensitivity. We present a detailed comparison between the gas distributions probed with ALMA and JWST in the primary outflow of IRAS 15398−3359. At 2000 au scale, the southwestern outflow shows four shell structures in 5–10 μ m continuum, whereas the submillimeter H 2 CO emission traces two of the four shells closest to the protostar. Submillimeter emission from CS, CCH, c–C 3 H 2 , and CH 3 OH shows the same two shells, and the 12 CO emission covers most of the outflow region. SO and SiO only trace a condensation at the edge of the shell closest to the protostar. None of these lines observed with ALMA show the outermost shell. At 500 au scale, we find hot H 2 gas inside the outflow cavity with JWST. The derived temperature of H 2 is 1147 ± 198 K within a 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>″</mml:mi> </mml:mrow> </mml:mover> </mml:math> 5 aperture at the protostar. The foreground mass column density of dust is (1.4–2.0) × 10 −3 g · cm −2 ( A V = 47–66 mag) in the outflow, using the dust model from J. C. Weingartner &amp; B. T. Draine (2001). We also find an 8 ∘ difference between the directions toward the [Fe ii ] knot and the outermost shell in the MIRI image, which may be interpreted as the precession of the [Fe ii ] jet. The dynamical timescale of the [Fe ii ] knot is 10 yr, suggesting a current event.