Hot cores in the outer Galaxy: impact of metallicity on the formation of complex organic molecules

Youxin, Wang

doi:10.5281/zenodo.17108857

Hot cores in the outer Galaxy: impact of metallicity on the formation of complex organic molecules

Youxin, Wang

Publisher: Zenodo
DOI: 10.5281/zenodo.17108857
Repository: zenodo.org
Language: en

Abstract

Many complex organic molecules (COMs) in star forming regions are believed to form on the surfaces of dust grains or in their ice mantles. Therefore, we expect both the reduced metallicity and dust-to-gas ratio in the outer Galaxy to have an impact on the chemical composition of these regions. To test this, we use NOEMA to perform an imaging spectral line survey of the hot core candidate G135.27+2.79 at a galactocentric distance of 13.1 kpc. Our NOEMA observations in the 1.3 mm range have led to the identification of 43 species, including their isotopologues and deuterated variants. Among these are COMs with up to nine atoms, detected toward a hot (>100 K) and compact (< 5000 au) region. These detections confirm G135.27+2.79 as the second known hot core in the outer Galaxy. The rotational temperatures and column densities of the detected molecules are derived under the LTE approximation. Hot-core simulations with the three-phase astrochemical code MAGICKAL with reduced metallicity and dust-to-gas ratio and under normal conditions predict that certain molecules have a significantly reduced abundance (relative to methanol) at low metallicity and dust-to-gas ratio while others keep a similar abundance. The model predictions are approximately consistent with our observations when we compare the COM abundances of G135.27+2.79 with those in hot cores/corinos within the Solar circle, suggesting that metallicity and dust-to-gas ratio do have an impact on the formation of COMs.

Full text

Hot cores in the outer Galaxy: impact of metallicity on the formation of complex organic molecules Youxin Wang (MPIfR) Collaborators: Arnaud Belloche (MPIfR), Robin Garrod (UVA) ESO, Garching 11 March, 2025 `@IRAM @IRAM ●Compact (< 0.1 pc) ● High density (> 106 cm-3) ●High gas/dust temperature (150-250 K) ● Rich spectrum, with many lines of COMs Credits: Cormac Purcell 1 Hot cores in high-mass star-forming regions ●Compact (< 0.1 pc) ● High density (> 106 cm-3) ●High gas/dust temperature (150-250 K) ● Rich spectrum, with many lines of COMs Credits: Cormac Purcell 1 Hot cores in high-mass star-forming regions excellent targets to study the chemical composition of the material involved in the formation of stars and planets 2 Similar chemical composition in the inner Galaxy (Jørgensen+2020) Sgr B2(N2): Galactic center IRAS 16293-2433B: Solar neighborhood (Luck & Lambert2011) (Giannetti+2017) 3 gas-to-dust mass ratio Low metallicity in the outer Galaxy Metallicity Gas-to-dust ratio (Luck & Lambert2011) (Giannetti+2017) 3 gas-to-dust mass ratio Low metallicity in the outer Galaxy Metallicity Gas-to-dust ratio Does metallicity have an impact on the prevalence of COMs in star-forming regions of our Galaxy? 4 Low metallicity in the outer Galaxy Predictions of astrochemical model MAGICKAL (Garrod+2022) (R. Garrod priv. comm.) (X/CH3OH)lowZ low metallicity (X/CH3OH)basic normal envir. whatever the warm-up model timescale: molecules with reduced abundance at low Z molecules ~ insensitive to Z R = 4 Low metallicity in the outer Galaxy Predictions of astrochemical model MAGICKAL (Garrod+2022) (R. Garrod priv. comm.) (X/CH3OH)lowZ low metallicity (X/CH3OH)basic normal envir. whatever the warm-up model timescale: molecules with reduced abundance at low Z molecules ~ insensitive to Z R = ⇒ use outer-Galaxy hot cores to test chemical model Observations ●Only one hot core known in the outer Galaxy (Shimonishi+21) 5 Search for hot cores in the outer Galaxy LTE synthetic spectra with Weeds, spectroscopic predictions from CDMS/LSD/JPL > Line width & Velocity offset > Temperature & Column density > Emission size 8 LTE modelling of the COM emission CH3OH CH3OH LTE synthetic spectra with Weeds, spectroscopic predictions from CDMS/LSD/JPL > Line width & Velocity offset > Temperature & Column density > Emission size 8 LTE modelling of the COM emission Trot = 175.4 ± 2.1 K N = (2.1 ± 0.1)x 1018 cm-2 CH3OH Compact (< 0.1 pc) High gas temperature Rich spectrum 9 G135.27: second hot core in the outer Galaxy Trot = 175.4 ± 2.1 K N = (2.1 ± 0.1)x 1018 cm-2 10 Bipolar outflow 12CO 13CO 11 Sgr B2(N2): Galactic center G31.41: inner Galaxy IRAS16293B: solar neighborhood Comparison with astrochemical models 11 Sgr B2(N2): Galactic center G31.41: inner Galaxy IRAS16293B: solar neighborhood Comparison with astrochemical models ⇒ Approximate agreement between the astrochemical models and the COM abundances (relative to CH3OH) of G135.27 relative to the three inner Galaxy sources (Sgr B2(N2), G31.41, and IRAS16293B) 12 Comparison with hot cores in the Milky Way - similar chemical composition between G31.41 and G135.27, but G135.27 has lower COMs abundance - COM abundances in G135.27 is between those of G31.41 and WB89-789 - much poorer correlation with SgrB2(N2) and IRAS16293B Summary ● NOEMA detection a second hot core in the outer Galaxy ● associated with bipolar outflow ●12 COMs are detected ● Approximate agreement with predictions of astrochemical model ● COM abundances in G135.27 (Dgc = 13.1 kpc) in between G31.41 (Dgc = 5 kpc) and WB89-789 (Dgc = 17 kpc) Summary ● NOEMA detection a second hot core in the outer Galaxy ● associated with bipolar outflow ●12 COMs are detected ● Approximate agreement with predictions of astrochemical model ● COM abundances in G135.27 (Dgc = 13.1 kpc) in between G31.41 (Dgc = 5 kpc) and WB89-789 (Dgc = 17 kpc) Outlook: two additional candidates observed with NOEMA Thanks for your attention! @ IRAM