Sagittarius B2(N), a gold mine to investigate the formation of complex organic molecules
Abstract
We used ReMocA, a sensitive imaging spectral line survey performed with ALMA over a broad frequency range at high angular resolution, to decipher the chemical composition of hot molecular cores in the high-mass star forming region Sgr B2(N). We derived the column densities of almost 50 (mainly organic) molecules (not counting isotopologs) as well as upper limits for about 150 species toward a compact group of four hot cores located in the sub-region Sgr B2(N2). We use this gold mine to explore the correlations (or lack thereof) between the four hot cores and between these sources and several other hot cores/corinos that have been studied in detail in the inner Galaxy. We also investigate the relationships within various families of molecules. We will report on the main findings of this study. Our goal is to provide useful constraints to astrochemical models in order to improve our understanding of the formation of complex organic molecules in star forming regions.
Full text
©B. Tafreshi / ESO Sagittarius B2(N), a goldmine to investigate the formation of complex organic molecules Arnaud Belloche Max-Planck-Institut f¨ ur Radioastronomie Towards new frontiers: the astrochemical journey from young stellar nurseries to exoplanets Garching, Germany 11 March 2025 fürRadioastronomie Max-Planck-Institut
2 / 12 In memory of Karl Menten (1957–2024) IKarl originally motivated the Sgr B2 spectral line surveys at MPIfR Iwe deeply miss his enthusiasm, his scientific curiosity and creativity, as well as his open and generous personality Iconference at Wasem Kloster Engelthal, Germany IAugust 18-22, 2025 Istar formation and evolution, on both local and global scales
2 / 12 In memory of Karl Menten (1957–2024) IKarl originally motivated the Sgr B2 spectral line surveys at MPIfR Iwe deeply miss his enthusiasm, his scientific curiosity and creativity, as well as his open and generous personality Iconference at Wasem Kloster Engelthal, Germany IAugust 18-22, 2025 Istar formation and evolution, on both local and global scales
3 / 12 The high mass star-forming region Sgr B2 Central Molecular Zone at 870 µm (ATLASGAL/LABOCA + Planck ©MPIfR/A. Weiß) Sgr B2(N) in thermal dust emission at 850 µm (SMA, Qin+ 2011) Ione of the most prominent star-forming regions in our Galaxy Icontains two dense clumps (N and M) that host protoclusters (hot cores, UC H II regions) Sgr B2(N) Itwo main hot cores (N1 and N2) (+ fainter ones: Bonfand+ 2017, S´ anchez-Monge+ 2017) Ihigh column densities (NH2∼1024–1025 cm−2over few arcsec) ⇒key advantage for detection of complex organic molecules (COMs)
3 / 12 The high mass star-forming region Sgr B2 Central Molecular Zone at 870 µm (ATLASGAL/LABOCA + Planck ©MPIfR/A. Weiß) Sgr B2(N) in thermal dust emission at 850 µm (SMA, Qin+ 2011) Ione of the most prominent star-forming regions in our Galaxy Icontains two dense clumps (N and M) that host protoclusters (hot cores, UC H II regions) Sgr B2(N) Itwo main hot cores (N1 and N2) (+ fainter ones: Bonfand+ 2017, S´ anchez-Monge+ 2017) Ihigh column densities (NH2∼1024–1025 cm−2over few arcsec) ⇒key advantage for detection of complex organic molecules (COMs)
3 / 12 The high mass star-forming region Sgr B2 Central Molecular Zone at 870 µm (ATLASGAL/LABOCA + Planck ©MPIfR/A. Weiß) Sgr B2(N) in thermal dust emission at 850 µm (SMA, Qin+ 2011) Ione of the most prominent star-forming regions in our Galaxy Icontains two dense clumps (N and M) that host protoclusters (hot cores, UC H II regions) Sgr B2(N) Itwo main hot cores (N1 and N2) (+ fainter ones: Bonfand+ 2017, S´ anchez-Monge+ 2017) Ihigh column densities (NH2∼1024–1025 cm−2over few arcsec) ⇒key advantage for detection of complex organic molecules (COMs)
4 / 12 (Re)Exploring Molecular Complexity with ALMA Ispectral line surveys of Sgr B2(N) over 84 – 114 GHz with ALMA in cycles 0/1 (EMoCA, resolution 1.600 ; Belloche+ 2016) and cycle 4 (ReMoCA, 0.600 ; Belloche+ 2019) Ifollow-up of our successful survey with IRAM 30 m telescope (Belloche+ 2008, 2009, 2013) Imain goals: understand the growth of molecular complexity in the ISM, search for new COMs, test astrochemical models (collaboration with R. Garrod) Inew COMs detected with EMoCA/ReMoCA (collaboration with spectroscopists): i-C3H7CN,CH3NHCHO,NH2C(O)NH2,i-C3H7OH (Belloche+ 2014, 2017, 2019, 2022) Ithis talk: insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2) (Belloche, Garrod, M¨ uller, Morin, Willis, & Menten, article recently submitted to A&A)
4 / 12 (Re)Exploring Molecular Complexity with ALMA Ispectral line surveys of Sgr B2(N) over 84 – 114 GHz with ALMA in cycles 0/1 (EMoCA, resolution 1.600 ; Belloche+ 2016) and cycle 4 (ReMoCA, 0.600 ; Belloche+ 2019) Ifollow-up of our successful survey with IRAM 30 m telescope (Belloche+ 2008, 2009, 2013) Imain goals: understand the growth of molecular complexity in the ISM, search for new COMs, test astrochemical models (collaboration with R. Garrod) Inew COMs detected with EMoCA/ReMoCA (collaboration with spectroscopists): i-C3H7CN,CH3NHCHO,NH2C(O)NH2,i-C3H7OH (Belloche+ 2014, 2017, 2019, 2022) Ithis talk: insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2) (Belloche, Garrod, M¨ uller, Morin, Willis, & Menten, article recently submitted to A&A)
4 / 12 (Re)Exploring Molecular Complexity with ALMA Ispectral line surveys of Sgr B2(N) over 84 – 114 GHz with ALMA in cycles 0/1 (EMoCA, resolution 1.600 ; Belloche+ 2016) and cycle 4 (ReMoCA, 0.600 ; Belloche+ 2019) Ifollow-up of our successful survey with IRAM 30 m telescope (Belloche+ 2008, 2009, 2013) Imain goals: understand the growth of molecular complexity in the ISM, search for new COMs, test astrochemical models (collaboration with R. Garrod) Inew COMs detected with EMoCA/ReMoCA (collaboration with spectroscopists): i-C3H7CN,CH3NHCHO,NH2C(O)NH2,i-C3H7OH (Belloche+ 2014, 2017, 2019, 2022) Ithis talk: insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2) (Belloche, Garrod, M¨ uller, Morin, Willis, & Menten, article recently submitted to A&A)
7 / 12 Chemical composition: correlations and outliers Composition: Iup to 24 COMs detected Correlations: Itight correlation AN02/AN03 Igood correlation N2b/AN06 but prominent outliers NH2CHO and HNCO Classes of molecule: O, O+N,N,C,S IAN03: poorer correlation of S-bearing content with other sources IAN06: underabundant O+N-bearing species
7 / 12 Chemical composition: correlations and outliers Composition: Iup to 24 COMs detected Correlations: Itight correlation AN02/AN03 Igood correlation N2b/AN06 but prominent outliers NH2CHO and HNCO Classes of molecule: O, O+N,N,C,S IAN03: poorer correlation of S-bearing content with other sources IAN06: underabundant O+N-bearing species
7 / 12 Chemical composition: correlations and outliers Composition: Iup to 24 COMs detected Correlations: Itight correlation AN02/AN03 Igood correlation N2b/AN06 but prominent outliers NH2CHO and HNCO Classes of molecule: O, O+N,N,C,S IAN03: poorer correlation of S-bearing content with other sources IAN06: underabundant O+N-bearing species
7 / 12 Chemical composition: correlations and outliers Composition: Iup to 24 COMs detected Correlations: Itight correlation AN02/AN03 Igood correlation N2b/AN06 but prominent outliers NH2CHO and HNCO Classes of molecule: O, O+N,N,C,S IAN03: poorer correlation of S-bearing content with other sources IAN06: underabundant O+N-bearing species
7 / 12 Chemical composition: correlations and outliers Composition: Iup to 24 COMs detected Correlations: Itight correlation AN02/AN03 Igood correlation N2b/AN06 but prominent outliers NH2CHO and HNCO Classes of molecule: O, O+N,N,C,S IAN03: poorer correlation of S-bearing content with other sources IAN06: underabundant O+N-bearing species
7 / 12 Chemical composition: correlations and outliers Composition: Iup to 24 COMs detected Correlations: Itight correlation AN02/AN03 Igood correlation N2b/AN06 but prominent outliers NH2CHO and HNCO Classes of molecule: O, O+N,N,C,S IAN03: poorer correlation of S-bearing content with other sources IAN06: underabundant O+N-bearing species
8 / 12 Radicals: stringent upper limits for models ×model predictions (MAGICKAL, Garrod+ 2022) ICH2CHO,CH2CN,C3N,NH2CO overproduced by the model ⇒lack of appropriate destruction mechanisms in the network, in particular reactions with atomic hydrogen (which the other radicals have)
8 / 12 Radicals: stringent upper limits for models ×model predictions (MAGICKAL, Garrod+ 2022) ICH2CHO,CH2CN,C3N,NH2CO overproduced by the model ⇒lack of appropriate destruction mechanisms in the network, in particular reactions with atomic hydrogen (which the other radicals have)
8 / 12 Radicals: stringent upper limits for models ×model predictions (MAGICKAL, Garrod+ 2022) ICH2CHO,CH2CN,C3N,NH2CO overproduced by the model ⇒lack of appropriate destruction mechanisms in the network, in particular reactions with atomic hydrogen (which the other radicals have)
8 / 12 Radicals: stringent upper limits for models ×model predictions (MAGICKAL, Garrod+ 2022) ICH2CHO,CH2CN,C3N,NH2CO overproduced by the model ⇒lack of appropriate destruction mechanisms in the network, in particular reactions with atomic hydrogen (which the other radicals have)
11 / 12 Chemical differentiation by class of molecule Itight correlation with G31.41 and IRAS16293B after normalizing by class of molecule Ipoor correlation with G+0.693, due to N-bearing molecules; S-bearing species more prominent in G+0.693 Ino correlation with TMC-1 Ilargest variance: N-bearing class (from tight correlation to no correlation; overall shifts w.r.t other classes) Ismallest variance: S-bearing class (tight correlation with G31.41, IRAS16293B, G+0.693; good correlation with TMC-1)
11 / 12 Chemical differentiation by class of molecule Itight correlation with G31.41 and IRAS16293B after normalizing by class of molecule Ipoor correlation with G+0.693, due to N-bearing molecules; S-bearing species more prominent in G+0.693 Ino correlation with TMC-1 Ilargest variance: N-bearing class (from tight correlation to no correlation; overall shifts w.r.t other classes) Ismallest variance: S-bearing class (tight correlation with G31.41, IRAS16293B, G+0.693; good correlation with TMC-1)
11 / 12 Chemical differentiation by class of molecule Itight correlation with G31.41 and IRAS16293B after normalizing by class of molecule Ipoor correlation with G+0.693, due to N-bearing molecules; S-bearing species more prominent in G+0.693 Ino correlation with TMC-1 Ilargest variance: N-bearing class (from tight correlation to no correlation; overall shifts w.r.t other classes) Ismallest variance: S-bearing class (tight correlation with G31.41, IRAS16293B, G+0.693; good correlation with TMC-1)
11 / 12 Chemical differentiation by class of molecule Itight correlation with G31.41 and IRAS16293B after normalizing by class of molecule Ipoor correlation with G+0.693, due to N-bearing molecules; S-bearing species more prominent in G+0.693 Ino correlation with TMC-1 Ilargest variance: N-bearing class (from tight correlation to no correlation; overall shifts w.r.t other classes) Ismallest variance: S-bearing class (tight correlation with G31.41, IRAS16293B, G+0.693; good correlation with TMC-1)
11 / 12 Chemical differentiation by class of molecule Itight correlation with G31.41 and IRAS16293B after normalizing by class of molecule Ipoor correlation with G+0.693, due to N-bearing molecules; S-bearing species more prominent in G+0.693 Ino correlation with TMC-1 Ilargest variance: N-bearing class (from tight correlation to no correlation; overall shifts w.r.t other classes) Ismallest variance: S-bearing class (tight correlation with G31.41, IRAS16293B, G+0.693; good correlation with TMC-1)
11 / 12 Chemical differentiation by class of molecule Itight correlation with G31.41 and IRAS16293B after normalizing by class of molecule Ipoor correlation with G+0.693, due to N-bearing molecules; S-bearing species more prominent in G+0.693 Ino correlation with TMC-1 Ilargest variance: N-bearing class (from tight correlation to no correlation; overall shifts w.r.t other classes) Ismallest variance: S-bearing class (tight correlation with G31.41, IRAS16293B, G+0.693; good correlation with TMC-1)
12 / 12 Conclusions Ilarge variance of class of N-bearing molecules among sources ⇒more sensitive than O-bearing or S-bearing classes to Ishocks (G+0.693) Ilow-T gas-phase chemistry after non-thermal desorption (TMC-1) Ior density (G+0.693, TMC-1) Isegregation between O-bearing and N-bearing species: partial desorption might encourage preferential release of outer ice layers that are rich in CO and related O-bearing species while leaving deeper, N-rich material in place →abundance shifts between N-bearing and O-bearing molecules may indicate how violently and completely the ice mantles are desorbed Iimprovements of chemical models needed to distinguish between ice layers beyond the typical bulk+surface-layer paradigm
12 / 12 Conclusions Ilarge variance of class of N-bearing molecules among sources ⇒more sensitive than O-bearing or S-bearing classes to Ishocks (G+0.693) Ilow-T gas-phase chemistry after non-thermal desorption (TMC-1) Ior density (G+0.693, TMC-1) Isegregation between O-bearing and N-bearing species: partial desorption might encourage preferential release of outer ice layers that are rich in CO and related O-bearing species while leaving deeper, N-rich material in place →abundance shifts between N-bearing and O-bearing molecules may indicate how violently and completely the ice mantles are desorbed Iimprovements of chemical models needed to distinguish between ice layers beyond the typical bulk+surface-layer paradigm
12 / 12 Conclusions Ilarge variance of class of N-bearing molecules among sources ⇒more sensitive than O-bearing or S-bearing classes to Ishocks (G+0.693) Ilow-T gas-phase chemistry after non-thermal desorption (TMC-1) Ior density (G+0.693, TMC-1) Isegregation between O-bearing and N-bearing species: partial desorption might encourage preferential release of outer ice layers that are rich in CO and related O-bearing species while leaving deeper, N-rich material in place →abundance shifts between N-bearing and O-bearing molecules may indicate how violently and completely the ice mantles are desorbed Iimprovements of chemical models needed to distinguish between ice layers beyond the typical bulk+surface-layer paradigm
12 / 12 Conclusions Ilarge variance of class of N-bearing molecules among sources ⇒more sensitive than O-bearing or S-bearing classes to Ishocks (G+0.693) Ilow-T gas-phase chemistry after non-thermal desorption (TMC-1) Ior density (G+0.693, TMC-1) Isegregation between O-bearing and N-bearing species: partial desorption might encourage preferential release of outer ice layers that are rich in CO and related O-bearing species while leaving deeper, N-rich material in place →abundance shifts between N-bearing and O-bearing molecules may indicate how violently and completely the ice mantles are desorbed Iimprovements of chemical models needed to distinguish between ice layers beyond the typical bulk+surface-layer paradigm