Multi-line observations of CH${}_3$OH, c-C${}_3$H${}_2$ and HNCO towards L1544: Dissecting the core structure with chemical differentiation

Abstract

Pre-stellar cores are the basic unit for the formation of stars and stellar systems. The anatomy of the physical and chemical structures of pre-stellar cores is critical for understanding the star formation process. L1544 is a prototypical pre-stellar core, which shows significant chemical differentiation surrounding the dust peak. We aim to constrain the physical conditions at the different molecular emission peaks. This study allows us to compare the abundance profiles predicted from chemical models together with the classical density structure of Bonnor-Ebert (BE) sphere. We conducted multi-transition pointed observations of CH${}_3$OH, c-C${}_3$H${}_2$ and HNCO with the IRAM 30m telescope, towards the dust peak and the respective molecular peaks of L1544. With non-LTE radiative transfer calculations and a 1-dimensional model, we revisit the physical structure of L1544, and benchmark with the abundance profiles from current chemical models. We find that the HNCO, c-C${}_3$H${}_2$ and CH${}_3$OH lines in L1544 are tracing progressively higher density gas, from $\sim$10${}^4$ to several times 10${}^5$ cm${}^{-3}$. Particularly, we find that to produce the observed intensities and ratios of the CH${}_3$OH lines, a local gas density enhancement upon the BE sphere is required. This suggests that the physical structure of an early-stage core may not necessarily follow a smooth decrease of gas density profile locally, but can be intercepted by clumpy substructures surrounding the gravitational center. Multiple transitions of molecular lines from different molecular species can provide a tomographic view of the density structure of pre-stellar cores. The local gas density enhancement deviating from the BE sphere may reflect the impact of accretion flows that appear asymmetric and are enhanced at the meeting point of large-scale cloud structures.

arXiv commentaccepted by A&A; 22 pages, 22 figures incl. appendices

References in corpus (52)

• emcee: The MCMC Hammer
• Control of star formation by supersonic turbulence
• A computer program for fast non-LTE analysis of interstellar line spectra
• From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey
• Cold Dark Clouds: The Initial Conditions for Star Formation
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• Our astrochemical heritage
• Molecular ions in L1544. II. The ionization degree
• Observing the gas temperature drop in the high-density nucleus of L 1544
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• The Formation of Low-Mass Binary Star Systems Via Turbulent Fragmentation
• Astrochemistry During the Formation of Stars
• The origin of complex organic molecules in prestellar cores
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions
• On the internal structure of starless cores. II. A molecular survey of L1498 and L1517B
• Dust as interstellar catalyst I. Quantifying the chemical desorption process
• Dynamics and Depletion in Thermally Supercritical Starless Cores
• Molecular ions in L1544. I. Kinematics
• Simulating star formation in molecular cores II. The effects of different levels of turbulence
• Deuterated methanol in the pre-stellar core L1544
• The dynamics of collapsing cores and star formation
• Chemical differentiation in a prestellar core traces non-uniform illumination
• Benchmarking spin-state chemistry in starless core models
• The observed chemical structure of L1544
• The Central 1000 au of a Pre-stellar Core Revealed with ALMA. II. Almost Complete Freeze-out
• High sensitivity maps of molecular ions in L1544: I. Deuteration of N2H+ and HCO+ and first evidence of N2D+ depletion
• The central 1000 AU of a pre-stellar core revealed with ALMA. I. 1.3 mm continuum observations
• Chemistry and Radiative Transfer of Water in Cold, Dense Clouds
• The origin of gas-phase HCO and CH3O radicals in prestellar cores
• Dark cloud cores and gravitational decoupling from turbulent flows
• Mapping deuterated methanol toward L1544: I. Deuterium fraction and comparison with modeling
• FRagmentation and Evolution of dense cores Judged by ALMA (FREJA). I (Overview). Inner $\sim$1000 au structures of prestellar/protostellar cores in Taurus
• Seeds of Life in Space (SOLIS). III. Zooming into the methanol peak of the pre-stellar core L1544
• Understanding the ${\mathrm{C}}_3{\mathrm{H}}_2$ cyclic-to-linear ratio in L1544
• Gravitationally unstable condensations revealed by ALMA in the TUKH122 prestellar core in the Orion A cloud
• A study of the $c$-${\mathrm{C}}_3\mathrm{HD}$/$c$-${\mathrm{C}}_3{\mathrm{H}}_2$ ratio in low-mass star forming regions
• Efficient methanol production on the dark side of a prestellar core
• Protostellar collapse of magneto-turbulent cloud cores: shape during collapse and outflow formation
• LOC program for line radiative transfer
• Evolutionary view through the starless cores in Taurus: deuteration in TMC 1-C and TMC 1-CP
• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Detection of extremely high density compact structure of prestellar cores and multiple substructures within
• Distribution of methanol and cyclopropenylidene around starless cores
• Methanol Mapping in Cold Cores: Testing Model Predictions
• The evolution of temperature and density structures of OB cluster-forming molecular clumps
• Shaken and stirred: the effects of turbulence and rotation on disc and outflow formation during the collapse of magnetised molecular cloud cores
• Analytical Methods for Measuring the Parameters of Interstellar Gas Using the Data of Methanol Observations
• ALMA ACA and Nobeyama observations of two Orion cores in deuterated molecular lines
• The Evolution of Cloud Cores and the Formation of Stars
• Mapping the H${}_2$D${}^{+}$ and N${}_2$H${}^{+}$ emission towards prestellar cores. Testing dynamical models of the collapse using gas tracers
• Spherically-symmetric, cold collapse: the exact solutions and a comparison with self-similar solutions

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• A 3D physico-chemical model of a pre-stellar core. I. Environmental and structural impact on the distribution of CH${}_3$OH and $c$-C${}_3$H${}_2$
• First detection of CHD${}_2$OH towards pre-stellar cores
• Role of Filamentary Structures in the Formation of Two Dense Cores, L1544 and L694-2
• Mapping Synthetic Observations to Prestellar Core Models: An Interpretable Machine Learning Approach
• High deuteration of methanol in L1544
• Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO
• Chemistry of Dark Molecular Clouds