Ubiquitous $\mathrm{N}{\mathrm{H}}_3$ supersonic component in L1688 coherent cores

Abstract

Context : Star formation takes place in cold dense cores in molecular clouds. Earlier observations have found that dense cores exhibit subsonic non-thermal velocity dispersions. In contrast, CO observations show that the ambient large-scale cloud is warmer and has supersonic velocity dispersions. Aims : We aim to study the ammonia ($\mathrm{N}{\mathrm{H}}_3$) molecular line profiles with exquisite sensitivity towards the coherent cores in L1688 in order to study their kinematical properties in unprecedented detail. Methods : We used $\mathrm{N}{\mathrm{H}}_3$ (1,1) and (2,2) data from the first data release (DR1) in the Green Bank Ammonia Survey (GAS). We first smoothed the data to a larger beam of 1' to obtain substantially more extended maps of velocity dispersion and kinetic temperature, compared to the DR1 maps. We then identified the coherent cores in the cloud and analysed the averaged line profiles towards the cores. Results : For the first time, we detected a faint (mean $\mathrm{N}{\mathrm{H}}_3$(1,1) peak brightness $<$0.25 K in $T_{MB}$), supersonic component towards all the coherent cores in L1688. We fitted two components, one broad and one narrow, and derived the kinetic temperature and velocity dispersion of each component. The broad components towards all cores have supersonic linewidths (${\mathcal{M}}_S\ge 1$). This component biases the estimate of the narrow dense core component's velocity dispersion by $\approx$28% and the kinetic temperature by $\approx$10%, on average, as compared to the results from single-component fits. Conclusions : Neglecting this ubiquitous presence of a broad component towards all coherent cores causes the typical single-component fit to overestimate the temperature and velocity dispersion. This affects the derived detailed physical structure and stability of the cores estimated from $\mathrm{N}{\mathrm{H}}_3$ observations.

Accepted for publication in Astronomy & Astrophysics on 06/07/2020. 15 pages, 16 figures, 1 table. Language edits from previous version

References in corpus (9)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• Observing the gas temperature drop in the high-density nucleus of L 1544
• An Ammonia Spectral Atlas of Dense Cores in Perseus
• Dynamics of Dense Cores in the Perseus Molecular Cloud
• The On The Fly Imaging Technique
• A Portrait of Cold Gas in Galaxies at 60pc Resolution and a Simple Method to Test Hypotheses That Link Small-Scale ISM Structure to Galaxy-Scale Processes
• A Large Scale Survey of NGC1333
• NH_3(1_0-0_0) in the pre-stellar core L1544

Cited by in corpus (10)

• PRODIGE -- Envelope to disk with NOEMA I. A 3000 au streamer feeding a Class I protostar
• PRODIGE -- Envelope to Disk with NOEMA II. Small-scale temperature structure and a streamer feeding the SVS13A protobinary using CH3CN and DCN
• An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion
• Flow of gas detected from beyond the filaments to protostellar scales in Barnard 5
• Neutral vs Ion Linewidths in Barnard 5: Evidence for Penetration by MHD Waves
• PRODIGE -- Envelope to Disk with NOEMA III. The origin of complex organic molecule emission in SVS13A
• Turbulence and Accretion: a High-resolution Study of the B5 Filaments
• Alignment of dense molecular core morphology and velocity gradients with ambient magnetic fields
• Magnetic field measurement in TMC-1C using 22.3 GHz CCS Zeeman splitting
• Deuterium fractionation in cold dense cores in the low-mass star forming region L1688