Methanol Mapping in Cold Cores: Testing Model Predictions

Abstract

Chemical models predict that in cold cores gas-phase methanol is expected to be abundant at the outer edge of the CO depletion zone, where CO is actively adsorbed. CO adsorption correlates with volume density in cold cores, and, in nearby molecular clouds, the catastrophic CO freeze-out happens at volume densities above 10${}^4$ cm${}^{-3}$. The methanol production rate is maximized there and its freeze-out rate does not overcome its production rate, while the molecules are shielded from UV destruction by gas and dust. Thus, in cold cores, methanol abundance should generally correlate with visual extinction that depends both on volume and column density. In this work, we test the most basic model prediction that maximum methanol abundance is associated with a local $A_V\simeq$4 mag in dense cores and constrain the model parameters with the observational data. With the IRAM 30 m antenna, we mapped the CH${}_3$OH (2-1) and (3-2) transitions toward seven dense cores in the L1495 filament in Taurus to measure the methanol abundance. We use the Herschel/SPIRE maps to estimate visual extinction, and the C${}^{18}$O(2-1) maps from Tafalla & Hacar (2015) to estimate CO depletion. We explored the observed and modeled correlations between the methanol abundances, CO depletion, and visual extinction varying the key model parameters. The modeling results show that hydrogen surface diffusion via tunneling is crucial to reproduce the observed methanol abundances, and the needed reactive desorption efficiency matches the one deduced from laboratory experiments.

Accepted for publication in ApJ

References in corpus (33)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• The origin of complex organic molecules in prestellar cores
• Binding energies: new values and impact on the efficiency of chemical desorption
• The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• On the internal structure of starless cores. II. A molecular survey of L1498 and L1517B
• Experimental evidence for Glycolaldehyde and Ethylene Glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions
• Modeling Sulfur Depletion in Interstellar Clouds
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
• Chains of dense cores in the Taurus L1495/B213 complex
• Depletion and low gas temperature in the L183 prestellar core : the N2H+ - N2D+ tool
• Formation of Complex Organic Molecules in Cold Interstellar Environments through non-diffusive grain-surface and ice-mantle chemistry
• The Different Structures of the Two Classes of Starless Cores
• Deuterated methanol in the pre-stellar core L1544
• Chemical differentiation in a prestellar core traces non-uniform illumination
• Shells, jets, and internal working surfaces in the molecular outflow from IRAS 04166+2706
• Efficient Production of S${}_8$ in Interstellar Ices: The effects of cosmic ray-driven radiation chemistry and non-diffusive bulk reactions
• The Effects of Molecular Anions on the Chemistry of Dark Clouds
• Probing changes of dust properties along a chain of solar-type prestellar and protostellar cores in Taurus with NIKA
• Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions
• A 3D view of the Taurus star-forming region by Gaia and Herschel: multiple populations related to the filamentary molecular cloud
• An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud : I. Physical Properties of Filaments and Dense cores
• The complex organic molecular content in the L1498 starless core
• The JCMT and Herschel Gould Belt Surveys: A comparison of SCUBA-2 and Herschel data of dense cores in the Taurus dark cloud L1495
• H2, CO, and Dust Absorption through Cold Molecular Clouds
• Gas-grain model of carbon fractionation in dense molecular clouds
• Influence of surface and bulk water ice on the reactivity of a water-forming reaction
• Effect of grain size distribution and size-dependent grain heating on molecular abundances in starless and pre-stellar cores
• Search for grain growth towards the center of L1544
• AVIATOR: Morphological object reconstruction in 3D. An application to dense cores