The Central 1000 au of a Pre-stellar Core Revealed with ALMA. II. Almost Complete Freeze-out

Abstract

Pre-stellar cores represent the initial conditions in the process of star and planet formation. Their low temperatures ($<$10 K) allow the formation of thick icy dust mantles, which will be partially preserved in the future protoplanetary disks, ultimately affecting the chemical composition of planetary systems. Previous observations have shown that carbon- and oxygen-bearing species, in particular CO, are heavily depleted in pre-stellar cores due to the efficient molecular freeze-out onto the surface of cold dust grains. However, N-bearing species such as NH${}_3$ and, in particular, its deuterated isotopologues, appear to maintain high abundances where CO molecules are mainly in solid phase. Thanks to ALMA, we present here the first clear observational evidence of NH${}_2$D freeze-out toward the L1544 pre-stellar core, suggestive of the presence of a"complete-depletion zone" within a $\simeq$1800 au radius, in agreement with astrochemical pre-stellar core model predictions. Our state-of-the-art chemical model coupled with a non-LTE radiative transfer code demonstrates that NH${}_2$D becomes mainly incorporated in icy mantles in the central 2000 au and starts freezing-out already at $\simeq$7000 au. Radiative transfer effects within the pre-stellar core cause the NH${}_2$D(1${}_{11}$-1${}_{01}$) emission to appear centrally concentrated, with a flattened distribution within the central $\simeq$3000 au, unlike the 1.3 mm dust continuum emission which shows a clear peak within the central $\simeq$1800 au. This prevented NH${}_2$D freeze-out to be detected in previous observations, where the central 1000 au cannot be spatially resolved.

accepted for publication in The Astrophysical Journal

References in corpus (24)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• Observing the gas temperature drop in the high-density nucleus of L 1544
• The ancient heritage of water ice in the solar system
• The cometary composition of a protoplanetary disk as revealed by complex cyanides
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• Cometary Chemistry and the Origin of Icy Solar System Bodies, the view after Rosetta
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
• Depletion and low gas temperature in the L183 prestellar core : the N2H+ - N2D+ tool
• Structure and kinematics of the Taurus star-forming region from Gaia-DR2 and VLBI astrometry
• The Different Structures of the Two Classes of Starless Cores
• The dynamics of collapsing cores and star formation
• The observed chemical structure of L1544
• The abundances of nitrogen-containing molecules during pre-protostellar collapse
• The central 1000 AU of a pre-stellar core revealed with ALMA. I. 1.3 mm continuum observations
• Why does ammonia not freeze out in the center of pre-stellar cores?
• Prestellar grain-surface origins of deuterated methanol in comet 67P/Churyumov-Gerasimenko
• The cosmic-ray ionisation rate in the pre-stellar core L1544
• Dust opacity variations in the pre-stellar core L1544
• NH_3(1_0-0_0) in the pre-stellar core L1544
• Collisional excitation of singly deuterated ammonia NH${}_2$D by H${}_2$
• LOC program for line radiative transfer
• Neutral vs Ion Linewidths in Barnard 5: Evidence for Penetration by MHD Waves
• Effect of grain size distribution and size-dependent grain heating on molecular abundances in starless and pre-stellar cores
• A correlation between chemistry, polarization and dust properties in the Pipe Nebula starless core FeSt 1-457

Cited by in corpus (41)

• Carbon-Chain Chemistry in the Interstellar Medium
• An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion
• The complex organic molecular content in the L1517B starless core
• Multi-line observations of CH${}_3$OH, c-C${}_3$H${}_2$ and HNCO towards L1544: Dissecting the core structure with chemical differentiation
• FAUST XVII: Super deuteration in the planet forming system IRS 63 where the streamer strikes the disk
• 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${}_2$
• Cyanopolyyne chemistry in the L1544 prestellar core: new insights from GBT observations
• A large (~1 pc) contracting envelope around the prestellar core L1544
• Chemistry and dynamics of the prestellar core L1544
• Linking the dust and chemical evolution: Taurus and Perseus -- New collisional rates for HCN, HNC, and their C, N, and H isotopologues
• Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
• Nitrogen fractionation in ammonia and its insights on nitrogen chemistry
• Tracking the ice mantle history in the Solar-type Protostars of NGC 1333 IRAS 4
• Non-Equilibrium Abundances Treated Holistically (NEATH): the molecular composition of star-forming clouds
• Broadband spectroscopy of astrophysical ice analogues: II. Optical constants of CO and CO${}_2$ ices in the terahertz and infrared ranges
• Bombardment of CO ice by cosmic rays: I. Experimental insights into the microphysics of molecule destruction and sputtering
• The initial magnetic criticality of prestellar cores
• Hunting pre-stellar cores with APEX: IRAS16293E (Oph464)
• A Survey of Deuterated Ammonia in the Cepheus Star-Forming Region L1251
• Tracing the contraction of the pre-stellar core L1544 with HC${}^{17}$O${}^{+}$ $J$ = 1-0 emission
• Dual-band Unified Exploration of Three CMZ Clouds (DUET). Cloud-wide census of continuum sources showing low spectral indices
• Laboratory spectroscopy of theoretical ices: Predictions for JWST and test for astrochemical models
• The first interferometric measurements of NH${}_2$D/NH${}_3$ ratio in hot corinos
• Insights into the first and second hydrostatic core stages from numerical simulations
• PRODIGE VI -- Envelope to Disk with NOEMA: VI. The Missing Sulfur Problem
• Complex Organic Molecules Formation in Cold Cores on Stochastically Heated Grains
• Broadband infrared spectroscopy of methanol isotopologues in pure, H2O-rich, and CO-rich ice analogues
• The Cosmic-Ray Induced Sputtering Process On Icy Grains
• Toward Unraveling Cyanopolyyne Surface Chemistry: A Preview on Isolated Systems From HC_{3}N to Ethyl Cyanide and Propylamine
• Deuterium fractionation in cold dense cores in the low-mass star forming region L1688
• Chemical constraints on the dynamical evolution of the cold core L694
• Hunting pre-stellar cores with APEX: overview
• Role of NH3 Binding Energy in the Early Evolution of Protostellar Cores
• High deuteration of methanol in L1544
• Neon is an inhibitor of CO hydrogenation in pre-stellar core conditions
• Research on the Interstellar Medium and Star Formation in the Galaxy: An Indian Perspective
• Deuterium fractionation and CO depletion in Barnard 5
• Unveiling Fiber Networks and Core Formation in the DR21 South Filament
• Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO
• Mapping Interstellar Ice Inventory toward Class 0 Protostars in Star-forming Region Orion A with JWST Data
• Chemistry of Dark Molecular Clouds