CORINOS. I. JWST/MIRI Spectroscopy and Imaging of a Class 0 Protostar IRAS 15398–3359

Abstract

The origin of complex organic molecules (COMs) in young Class 0 protostars has been one of the major questions in astrochemistry and star formation. While COMs are thought to form on icy dust grains via gas-grain chemistry, observational constraints on their formation pathways have been limited to gas-phase detection. Sensitive mid-infrared spectroscopy with JWST enables unprecedented investigation of COM formation by measuring their ice absorption features. Mid-infrared emission from disks and outflows provide complementary constraints on the protostellar systems. We present an overview of JWST/Mid-Infrared Instrument (MIRI) Medium Resolution Spectroscopy (MRS) and imaging of a young Class 0 protostar, IRAS 15398−3359, and identify several major solid-state absorption features in the 4.9–28 μm wavelength range. These can be attributed to common ice species, such as H2O, CH3OH, NH3, and CH4, and may have contributions from more complex organic species, such as C2H5OH and CH3CHO. In addition to ice features, the MRS spectra show many weaker emission lines at 6–8 μm, which are due to warm CO gas and water vapor, possibly from a young embedded disk previously unseen. Finally, we detect emission lines from [Fe ii], [Ne ii], [S i], and H2, tracing a bipolar jet and outflow cavities. MIRI imaging serendipitously covers the southwestern (blueshifted) outflow lobe of IRAS 15398−3359, showing four shell-like structures similar to the outflows traced by molecular emission at submillimeter wavelengths. This overview analysis highlights the vast potential of JWST/MIRI observations and previews scientific discoveries in the coming years.

Simulation of CH$_3$OH ice UV photolysis under laboratory conditions

“…Methanol (CH 3 OH) ice has been securely detected in the interstellar medium (ISM) towards different lines of sight (e.g., Schutte et al 1991;Chiar et al 2000;Pontoppidan et al 2004;Boogert et al 2011;Perotti et al 2020Perotti et al , 2021Chu et al 2020;Goto et al 2021;Kim et al 2022). We highlight recent detection made with James Webb Space Telescope (JWST) observations, towards the Class 0 protostar IRAS 15398-3359 (program 2151, PI: Y.-L. Yang;Yang et al 2022) and in the densest regions of the molecular clouds Chameleon I (McClure et al 2023) as part of the Early Release Science (ERS) Ice Age program (PIs: M. Mcclure, A. Boogert, H. Linnartz). This simple alcohol is mostly formed via successive CO hydrogenation (Watanabe & Kouchi 2002;Fuchs et al 2009) through "dark ice chemistry" (Ioppolo et al 2021), a term used to characterize molecular synthesis without the influence of ionizing radiation.…”

The Kinematics and Excitation of Infrared Water Vapor Emission from Planet-forming Disks: Results from Spectrally Resolved Surveys and Guidelines for JWST Spectra

“…MIRI covers both CO and water in a single spectrum (e.g., Figure 1; see first detection in Yang et al 2022), avoiding uncertainties in flux calibration and variability that currently affect data obtained from the ground at different times and with different instruments (Section 4). However, MIRI only covers the high-J levels of 12 CO lines at >4.9 μm (P25 and up, or E u > 4700 K) and of 13 CO (P15 and up, or E u > 3500 K).…”

“…3. When observing CO in MIRI spectra, it should be kept in mind that only the high-J lines at E u > 4700 K are covered (Yang et al 2022), and that these are typically dominated by the BC and are not a good match to the rotational water lines at >10 μm. To measure empirical H 2 O/CO ratios from MIRI spectra alone, water lines from the rovibrational band at 6.5 μm and similar E u ≈ 5000 K may need to be used.…”

“…In this work we offer a contribution to this field at a time when the first water spectra are being observed with JWST (Yang et al 2022). We present and analyze spectrally resolved water emission lines from rovibrational and rotational bands at multiple wavelengths between 2.9 and 12.9 μm tracing upperlevel energies between 4000 and 9500 K, and compare them to the velocity and excitation of rovibrational CO spectra observed at 4.5-5.25 μm tracing the same range in upper-level energies.…”

An Ice Age JWST inventory of dense molecular cloud ices

“…There is excellent agreement between the column densities derived from both methanol features (See Supplementary Figure 2). Although the 6 and 6.85 µm features appear smooth at R∼100 in both sources, there are weak but robust absorption excesses at 6.94, 7.06, 7.24, and 7.43 µm, (see Figure 3), attributable to the functional group in COMs caused by the asymmetric deformation mode of CH 3 31 , which has been tentatively detected with Spitzer 14 and JWST 32 . These two bands are seen in the IR spectra of acetone (CH 3 COCH 3 ) 33 , ethanol (CH 3 CH 2 OH) 31 , and acetaldehyde (CH 3 CHO) 31 .…”