JOYS: Linking the molecular ice and gas-phase composition towards the high-mass hot core IRAS 18089-1732

Abstract

Context. The formation and destruction of molecules in the interstellar medium is a complex interplay between gas-phase reactions as well as processes on grain surfaces and within icy mantles. For many decades, the gas-phase composition of the cold material towards star-forming regions could be well characterized using (sub)mm facilities. Prior to the launch of the James Webb Space Telescope (JWST), ice species other than the main constituents (H2O, CO, CO2, NH3, CH4, CH3OH) were challenging to detect due to insufficient sensitivity as well as angular and/or spectral resolution. Aims. We determine molecular ice and gas-phase column densities towards the young and embedded high-mass hot core IRAS 18089-1732 within a region of 5000 au. Methods. We use spectroscopic data from 5-28 micron obtained with JWST to derive ice column densities of H2O, SO2, OCN-, CH4, HCOO-, HCOOH, CH3CHO, CH3COOH, C2H5OH, CH3OCH3, and CH3COCH3. Gas-phase column densities of a total of 38 molecules, including, O-, N-, S-, and Si-bearing species as well as less abundant isotopologues, are inferred from sensitive molecular line observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) at 3 mm wavelengths. Results. We find comparable abundances (relative to C2H5OH or CH3OH) in both phases for C2H5OH, CH3OH, and CH3OCH3. The abundances of SO2 and CH3COCH3 are higher in the gas-phase suggesting additional gas-phase formation routes. The abundance of CH3CHO is one order of magnitude higher in the ices compared to the gas-phase. The ice abundances (relative to H2O ice) towards the IRAS 18089 hot core are similar to previously studied Galactic low- and high-mass protostars. There are hints of a decreasing abundance with Galactocentric distance for OCN-, CH3OH, and CH3CHO ice. (abridged)

Figures (17)

• Figure 1: IRAS18089 continuum images (left: ALMA 3 mm, center: JWST/MIRI-MRS 5$\upmu$m, right: JWST/MIRI-MRS 19$\upmu$m). In all panels the black contours are the ALMA 3 mm continuum with steps from 5, 10, 20, 40, 80, 160, 320$\times\sigma_\mathrm{cont}$. The mm and MIR continuum peak positions are labeled and highlighted in red and pink. The red circle shows the aperture (1$"$ radius) used for spectra extraction towards the mm source. A scale bar in the top left panel marks a spatial scale of 5 000 au. The ellipse in the bottom left corner highlights the angular resolution of each data set.
• Figure 2: Removal of gas-phase lines and local continuum estimate. The top panel shows the contribution of gas-phase SO$_{2}$ emission (yellow) and CH$_4$ absorption (red) lines estimated from the observed IRAS 18089 mm spectrum (grey). The corrected spectrum is shown in black. The bottom panel presents the corrected optical depth spectrum (black) and the local continuum interpolation (blue line). The red dots mark the guiding points used for the interpolation. The green dashed line shows the continuum interpolation based on a 5th order polynomial (Appendix \ref{['app:testsice']}).
• Figure 3: Laboratory spectra before (dashed) and after (solid) baseline correction. Each spectrum is normalized to its peak optical depth with offsets added for all ice mixtures. Details on the laboratory spectra are summarized in Table \ref{['tab:ice_references']}.
• Figure 4: ALMA 3 mm spectra of SPR1 towards IRAS 18089 mm. In all panels, the observed ALMA spectrum extracted from the mm peak position is shown in black. The best-fit model obtained with xclass is shown in red taking into account all molecules. The $5\sigma_\mathrm{line}$ level is highlighted by the horizontal green line. Vertical lines mark molecular transitions considered in the xclass fit with peak intensities $>5\sigma_\mathrm{line}$. Optically thick lines excluded from the fit are grey-shaded.
• Figure 5: The same as Fig. \ref{['fig:alma']}, but for SPR2. For the three broadband spws an additional zoom in panel is shown to highlight the fainter lines.