Chemical complexity in star formation induced by stellar feedback: cores shock-formed by the supernova remnant W44

TL;DR

This study addresses how slow shocks from the supernova remnant W44 influence chemical complexity in prospective star-forming cores. Using broad, high-sensitivity 3 mm and 7 mm surveys with IRAM-30m and Yebes-40m, and leveraging a MIREX mass-surface-density map, the authors identify deuterated species and several complex organic molecules toward the shock-impacted Clump at the W44–G034.77-00.55 interface, deriving $N(X)$ and $N(H_2)$ to compute abundances. They find $D/H$ ratios in the range $0.01-0.09$ and a modest inventory of COMs with $T_{ex}$ between $5$ and $13$ K, consistent with an early, pre-stellar or very early protostellar stage; COM abundances relative to CH$_3$OH are broadly comparable to those in comets and low-mass starless cores. The results suggest that SNR-driven shocks can set the physical and chemical conditions for star formation, with a chemical budget potentially preserved into later stages of planetary system formation, while also marking the first detection of COMs in a site of SNR–cloud interaction. Follow-up high-angular-resolution observations are needed to separate core emission from shocked gas and to confirm the evolutionary status of the Clump.

Abstract

Low-velocity shocks from Supernova Remnants (SNRs) may set the physical and chemical conditions of star formation in molecular clouds. Recent evidence suggests that the Sun might have formed through this process. However, the chemical conditions of shock-induced star forming region remain poorly constrained. We study the chemical complexity of a shock-impacted clump, with potential to yield star formation, named the Clump, and located at the interface between the SNR W44 and the infrared dark cloud G034.77-00.55. We test whether the Clump has chemical properties consistent with those observed in star forming regions unaffected by SNRs. We use high-sensitivity, broad spectral surveys at 3 and 7 mm obtained with the 30m antenna at IIRAM and the 40 m YEBES antenna, to identify D-bearing species and complex organic molecules (COMs) toward the Clump. For all species, we estimate molecular abundances and compare them with those observed across star forming regions at different evolutionary stages and masses, as well as comets. We detect multiple deuterated molecules (DCO+, DNC, DCN, CH2DOH) and COMs (CH3OH, CH3CHO, CH3CCH, CH3CN, CH3SH) with excitation temperatures of 5-13 K. To the best of our knowledge, this is the first detection of COMs toward a site of SNR-cloud interaction. The derived D/H ratios (0.01-0.04) and COM abundances are consistent with those reported toward typical low-mass starless cores and comparable to cometary values. The overall level of chemical complexity is relatively low, in line with an early evolutionary stage. We suggest that the Clump is a early stage shock-induced low-mass star forming region, not yet protostellar. We speculate that SNR shocks may set the physical and chemical conditions to form stars. The resulting chemical budget may be preserved along the formation process of a planetary system, being finally incorporated into planetesimals and cometesimals.

Figures (6)

• Figure 1: Top Left: Three colour image of G34.77. Red is 24 $\mu$m emission from the MIPSGAL survey carey2009, green is 8 $\mu$m emission from the GLIMPSE survey churchwell2009 and blue is 1 GHz continuum emission from the THOR survey beuther2016. Top Right: Mass surface density map kainulainen2013 with the red circle indicating the location of the Clump. Bottom panels: Zoom-in views of the Clump at 2 $\mu$m Skrutskie2006, 8 $\mu$m carey2009, 24 $\mu$m churchwell2009 and 70 $\mu$m Molinari2010 emission. The cyan contours correspond to a mass surface density value of 0.3 g cm$^{-2}$. In all panels, the magenta contour corresponds to a mass surface density of 0.1 g cm$^{-2}$ and highlights the cloud outskirts. The red circle size corresponds to 44$^{\prime\prime}$, i.e. the largest beam size in the Yebes-40m observations.
• Figure 2: Rotational diagrams obtained using madcuba for $^{13}$CH$_3$OH, CH$_3$CCH, CH$_3$CHO, CH$_3$CN and CH$_3$SH. Magenta empty squares indicate the data points, while the green lines show the best fitting found by madcuba. In all panels, the corresponding species is indicated together with the inferred excitation temperature, $T_{\mathrm{ex}}$ and total column density, $N_{\mathrm{tot}}$.
• Figure 3: D/H ratios measured from DCO$^+$, DNC, DCN and CH$_2$DOH toward the Clump (dashed black lines and grey shadows) compared with literature values across low-mass starless/pre-stellar cores and low-mass protostars, high-mass IR-dark clump, high-mass protostellar objects and comets. For reference, the cosmic D/H ratio oliveira2003 and the D/H measured in meteorites (red shadow) and proto-solar nebula (dotted cyan line) are reported.
• Figure 4: Comparison between COM abundances with respect to CH$_3$OH measured toward the Clump and literature values toward L1544 Vastel2014Bizzocchi2014jimenezserra2016Vastel2019, TMC-1 Gratier2016Cabezas2021Agundez2025, I00117-MM2 and G11.11 Vasyunina2014fontani2015Mininni2021, IRAS 16293B (hot corino) and G32.41+0.31 Mininni2023LopezGallifa2024, and the comets 67P/Churyumov–Gerasimenko and Hale–Bopp BockeleeMorvan2000LeRoy2015Altwegg2017. Colors are representative of the environment: orange and dark orange for low-mass cores and dark clouds, green and dark green for massive cores/IRDCs, blue and dark blue for more evolved hot cores and corinos, pink and purple for comets.
• Figure 5: Spectra of detected D-bearing species and their H-bearing counterparts. For clarity, we only indicate the species, while quantum numbers for each transitions are reported in Table \ref{['tab:LineList']}.