Chemical evolution in high-mass star-forming regions

TL;DR

This review synthesizes observational and theoretical progress on chemical evolution in high-mass star-forming regions, highlighting how line and source surveys, along with advanced chemical modelling, link molecular inventories to physical evolution from HMSCs through HMPOs to HC/UC H II regions. It emphasizes the pivotal role of temperature rise, grain-surface chemistry, and UV irradiation in shaping chemical complexity, including widespread COMs and deuterated species that serve as evolution tracers. Key findings include: deuterium fractionation declines with evolution, COMs proliferate in the warm HMPO/HMC phases, and internal PDRs in HC/UC H II regions drive UV-dominated chemistry that complicates simple molecular clocks. The significance lies in constraining massive-star formation timescales, informing the chemical heritage inherited by planetary systems, and guiding future JWST/ALMA surveys and self-consistent gas-grain–radiative-transfer models for a holistic view of astrochemical evolution.

Abstract

Growing evidence shows that most stars in the Milky Way, including the Sun, are born in high-mass star-forming regions, but due to both observational and theoretical challenges, our understanding of their chemical evolution is much less clear than that of their low-mass counterparts. Thanks to the capabilities of new generation telescopes and computers, a growing amount of observational and theoretical results have been recently obtained, which have important implications not only for our understanding of the (still mysterious) formation process of high-mass stars, but also for the chemistry that the primordial Solar System might have inherited from its birth environment. In this review, we summarise the main observational and theoretical results achieved in the last decades in the study of chemistry evolution in high-mass star-forming regions, and in the identification of chemical evolutionary indicators. Emphasis is especially given to observational studies, for which most of the work has been carried out so far. A comparison with the chemical evolution occurring in other astrophysical environments, in particular in low-mass star-forming cores and extragalactic cores, is also briefly presented. Current open questions and future perspectives are discussed.

Figures (7)

• Figure 1: Scheme of the coarse evolutionary classification for high-mass star-forming cores, adapted from beuther07, following the labelling adopted in Sect. \ref{['intro']}. Adapted from colzi20.
• Figure 2: IRDC G11.11$-$0.12. ( Left) $Spitzer$ three-color composite image (24 $\mu$m, red, 8 $\mu$m, green, 4.5 $\mu$m, blue) of IRDC G11.11$-$0.12, also known as the ‘‘Snake’’ nebula. The two more massive clumps embedded in this cloud, named P1 and P6, are indicated. ( Right) SMA spectra at 1.3 mm toward the protostellar cores and the prestellar core candidates embedded in P1 and P6, with identification of the detected species. Adapted from wang14.
• Figure 3: GUAPOS survey. Full ALMA Band 3 (3 mm) spectrum (black histogram) of the G31.41+0.31 HMC from 84 GHz to 116 GHz adapted from mininni20 and colzi21. The red solid line is the best fit for all the species detected.
• Figure 4: Comparison of the IRAM 30-m spectra at 3 mm and 2 mm toward the H ii regions in Cep A, DR21S, S76E and G34. Adapted from li17.
• Figure 5: Panel (a), from top to bottom: comparison between the mean D/H ratio (black symbols) computed from N$_{2}$H$^{+}$ (first panel), HNC (second panel), NH$_3$ (third panels), and CH$_3$OH (fourth panels). The mean values have been computed for the evolutionary groups HMSC, HMPO, and UC H ii (Fig. \ref{['fig:Fig1']}). Cold and warm HMSCs, namely cores with kinetic temperatures lower and higher than 20 K, respectively, have been treated separately. The error bars indicate the standard deviation. The grey arrows represent mean upper limits for those evolutionary groups in which no sources have been detected. The red dot in the fourth panel represents a doubtful CH$_2$DOH detection. The red arrows in each frame illustrate roughly the tentative evolutionary trends. Adapted from Fontani et al. (2015a). Panel (b), top: evolutionary trends observed by sabatini24 of o-H$_2$D$^+$ (blue symbols) and N$_{2}$D$^{+}$ (red symbols) as a function of the evolutionary class. Circles and diamonds refer to results from sabatini24 and giannetti19, respectively. Panel (b), bottom: median $R_{\rm D}$ factors derived for each evolutionary class. Different colours refer to values obtained from LTE and Non-LTE analysis discussed in sabatini24.