Chemical diversity of prestellar cores in Orion B
Abstract
The densest and coldest regions of molecular clouds, though seemingly inactive, often contain prestellar cores that exhibit emission of various chemical species indicative of star formation processes. The Orion B molecular cloud is a laboratory of different environments, from UV-illuminated to cold and shielded, which directly contributes to the diversity of sources forming there. In this talk, I will present the results of an analysis based on the observations of the ORION-B observational programme performed with the IRAM 30m telescope (Pety et al., 2017; Einig et al., 2023). A sample of pre-stellar cores and protostars was selected based on the Herschel catalogue (Konyves et al., 2020), and their molecular line emission was characterised for selected species, including four CO isotopologues, organic compounds such as H2CO and CH3OH, nitrogen-bearing species like N2H+ and HNC, and deuterated species including DCO+ and DNC. The abundances measured in the local thermodynamic equilibrium (LTE) scenario will be presented, as well as those measured for a selected number of cores using a non-LTE multilayer model (Segal et al., 2024). General trends indicate a strong diversity of sources and chemical species, as evidenced by CO depletion and environmental dependence as traced by dust temperatures. These results along with their interpretations will be presented during the talk.
Full text
Chemical diversity of prestellar cores and protostars in the Orion B molecular cloud Helena Mazurek 2st Year PhD student Observatoire de Paris LUX laboratory March 10, 2025 Helena Mazurek (LUX, Paris) March 10, 2025 1 / 20
Presentation outline 1Project overview 2Source selection 3General statistics of tracers 4PCA analysis 5Abundances and depletion effect 6Summary and outlook Helena Mazurek (LUX, Paris) March 10, 2025 2 / 20
Presentation outline 1Project overview 2Source selection 3General statistics of tracers 4PCA analysis 5Abundances and depletion effect 6Summary and outlook Helena Mazurek (LUX, Paris) March 10, 2025 3 / 20
Orion Molecular Cloud Complex View on the constellation of Orion Image credit: Rogelio Bernal Andreo Top: Optical view on Orion B Image credit: Alan Smallbone Bottom: Molecular emission of 12CO,C18 O,N2H+ Helena Mazurek (LUX, Paris) March 10, 2025 4 / 20
Orion Molecular Cloud Complex View on the constellation of Orion Image credit: Rogelio Bernal Andreo Top: Optical view on Orion B Image credit: Alan Smallbone Bottom: Molecular emission of 12CO,C18 O,N2H+ Helena Mazurek (LUX, Paris) March 10, 2025 4 / 20
Orion Molecular Cloud Complex View on the constellation of Orion Image credit: Rogelio Bernal Andreo Top: Optical view on Orion B Image credit: Alan Smallbone Bottom: Molecular emission of 12CO,C18 O,N2H+ Helena Mazurek (LUX, Paris) March 10, 2025 4 / 20
ORION-B project Millimetre-wave observational programme mapping a large fraction of the Orion B giant molecular cloud •40 GHz spectral coverage and a field of view of 5 degrees squared at ∼30” resolution •25 molecular tracers from different families of molecular species (ex. CO, nitrogen bearing N2H+, organic CH3OH, H2CO) •Selected fields covered also by (2-1) observations of 12CO,13CO and C18O Full field of view of ORION-B observations in different CO isotolopologues (12CO, 13 CO,C18O) Helena Mazurek (LUX, Paris) March 10, 2025 5 / 20
ORION-B project: Chemical diversity of prestellar cores and protostars Millimetre-wave observational programme mapping a large fraction of the Orion B giant molecular cloud •40 GHz spectral coverage and a field of view of 5 degrees squared at ∼30” resolution •25 molecular tracers from different families of molecular species (ex. CO, nitrogen bearing N2H+, organic CH3OH, H2CO) •Selected fields covered also by (2-1) observations of 12CO,13CO and C18O Full field of view of ORION-B observations in different CO isotolopologues (12CO, 13 CO,C18O) Characterisation of prestellar cores and protostars using molecular tracers and additional environmental parameters (NH2,n,Tdust,G0) to understand the underlying reason for their diversity Helena Mazurek (LUX, Paris) March 10, 2025 5 / 20
Presentation outline 1Project overview 2Source selection 3General statistics of tracers 4PCA analysis 5Abundances and depletion effect 6Summary and outlook Helena Mazurek (LUX, Paris) March 10, 2025 6 / 20
Presentation outline 1Project overview 2Source selection 3General statistics of tracers 4PCA analysis 5Abundances and depletion effect 6Summary and outlook Helena Mazurek (LUX, Paris) March 10, 2025 11 / 20
PCA analysis To combine the information from the many tracers available and derive a common axis of variation between the sources, we performed Principal Component Analysis on our data As input we used the measured fluxes transformed with a×arcsinh(x/a), in which a is scaled by the median noise in the dataset. This transformation ensures that the values are more evenly distributed, so that the highest values or ”missing” values do not drive the variance The first 3 components explain over 85% of the variation in the data Helena Mazurek (LUX, Paris) March 10, 2025 12 / 20
Contribution of each line to the first 3 PCs 0.50 0.25 0.00 0.25 0.50 PC1 70.3 % 0.50 0.25 0.00 0.25 0.50 PC2 8.35 % 12CO(1 0) 13CO(1 0) C18O(1 0) C17O(1 0) HCO HCO+(1 0) H2CO HNCO C3H2 CH3OH(2 1) H13CO+(1 0) DCO+(1 0) HCN(1 0) H13CN(1 0) HNC(1 0) HN13C(1 0) N2H+(1 0) 12CN(1 0) DNC(1 0) 12CS(2 1) CCH(1 0) 32SO(2 1) SiO(2 1) HCS+(1 0) CCS 0.50 0.25 0.00 0.25 0.50 PC3 6.94 % PC contribution per source NH2,Tdust Core tracers UV tracers Helena Mazurek (LUX, Paris) March 10, 2025 13 / 20
How “robust” are the selected sources? 0.50 0.25 0.00 0.25 0.50 PC1 70.3 % 0.50 0.25 0.00 0.25 0.50 PC2 8.35 % 12CO(1 0) 13CO(1 0) C18O(1 0) C17O(1 0) HCO HCO+(1 0) H2CO HNCO C3H2 CH3OH(2 1) H13CO+(1 0) DCO+(1 0) HCN(1 0) H13CN(1 0) HNC(1 0) HN13C(1 0) N2H+(1 0) 12CN(1 0) DNC(1 0) 12CS(2 1) CCH(1 0) 32SO(2 1) SiO(2 1) HCS+(1 0) CCS 0.50 0.25 0.00 0.25 0.50 PC3 6.94 % Robust sample 0.40 0.15 0.10 0.35 0.60 PC1 60.14 % 0.40 0.15 0.10 0.35 0.60 PC2 13.26 % 12CO(1 0) 13CO(1 0) C18O(1 0) C17O(1 0) HCO HCO+(1 0) H2CO HNCO C3H2 CH3OH(2 1) H13CO+(1 0) DCO+(1 0) HCN(1 0) H13CN(1 0) HNC(1 0) HN13C(1 0) N2H+(1 0) 12CN(1 0) DNC(1 0) 12CS(2 1) CCH(1 0) 32SO(2 1) SiO(2 1) HCS+(1 0) CCS 0.40 0.15 0.10 0.35 0.60 PC3 8.98 % Starless cores The pre-selection of cores on continuum data captures the most diverse and likely star-forming cores, which is confirmed by the PCA applied to the molecular data Helena Mazurek (LUX, Paris) March 10, 2025 14 / 20
How “robust” are the selected sources? 0.50 0.25 0.00 0.25 0.50 PC1 70.3 % 0.50 0.25 0.00 0.25 0.50 PC2 8.35 % 12CO(1 0) 13CO(1 0) C18O(1 0) C17O(1 0) HCO HCO+(1 0) H2CO HNCO C3H2 CH3OH(2 1) H13CO+(1 0) DCO+(1 0) HCN(1 0) H13CN(1 0) HNC(1 0) HN13C(1 0) N2H+(1 0) 12CN(1 0) DNC(1 0) 12CS(2 1) CCH(1 0) 32SO(2 1) SiO(2 1) HCS+(1 0) CCS 0.50 0.25 0.00 0.25 0.50 PC3 6.94 % Robust sample 0.40 0.15 0.10 0.35 0.60 PC1 60.14 % 0.40 0.15 0.10 0.35 0.60 PC2 13.26 % 12CO(1 0) 13CO(1 0) C18O(1 0) C17O(1 0) HCO HCO+(1 0) H2CO HNCO C3H2 CH3OH(2 1) H13CO+(1 0) DCO+(1 0) HCN(1 0) H13CN(1 0) HNC(1 0) HN13C(1 0) N2H+(1 0) 12CN(1 0) DNC(1 0) 12CS(2 1) CCH(1 0) 32SO(2 1) SiO(2 1) HCS+(1 0) CCS 0.40 0.15 0.10 0.35 0.60 PC3 8.98 % Starless cores The pre-selection of cores on continuum data captures the most diverse and likely star-forming cores, which is confirmed by the PCA applied to the molecular data Helena Mazurek (LUX, Paris) March 10, 2025 14 / 20
Presentation outline 1Project overview 2Source selection 3General statistics of tracers 4PCA analysis 5Abundances and depletion effect 6Summary and outlook Helena Mazurek (LUX, Paris) March 10, 2025 15 / 20
Excitation temperatures and abundances: observations Four fields covered by (2-1) observations. Cores and protostars are annotated with black and yellow crosses, respectively. Complementary observations of C18O(2−1) provide additional information needed to derive excitation temperature In an optically thin LTE scenario, this is enough to estimate the column densities Helena Mazurek (LUX, Paris) March 10, 2025 16 / 20
Excitation temperatures and abundances Despite cores being exposed to different environments, they appear to be depleted in all studied regions. However, this requires further verification, as in some cases this effect is probably related to photodissociation Depletion upper and lower limits from Fuente+12 (red dashed line). Median relative abundance wrt. NH2(green dashed line) Helena Mazurek (LUX, Paris) March 10, 2025 17 / 20
Excitation temperatures and abundances Despite cores being exposed to different environments, they appear to be depleted in all studied regions. However, this requires further verification, as in some cases this effect is probably related to photodissociation Depletion upper and lower limits from Fuente+12 (red dashed line). Median relative abundance wrt. NH2(green dashed line) Helena Mazurek (LUX, Paris) March 10, 2025 17 / 20
Multi-layer radiative transfer model* In order to get the best estimates of column densities, volume densities and temperatures for all cores in our sample, we use a multilayer radiative transfer model (“sandwich model‘’, Segal+24) that decomposes the emission profile into dense structures (filaments/core) and the surrounding gas layers The current configuration includes species with low (CO isotopologues) and high (HCO+) dipole moments to ensure sensitivity to a wide range of physical conditions. Once the physical conditions are determined, the emission lines of other species such as N2H+, DCO+etc. will be fitted with a sandwich or 1D model Helena Mazurek (LUX, Paris) March 10, 2025 18 / 20