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

Abstract

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.

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