Characterization of Infrared Dark Clouds -- NH${}_3$ Observations of an Absorption-contrast Selected IRDC Sample

Abstract

Despite increasing research in massive star formation, little is known about its earliest stages. Infrared Dark Clouds (IRDCs) are cold, dense and massive enough to harbour the sites of future high-mass star formation. But up to now, mainly small samples have been observed and analysed. To understand the physical conditions during the early stages of high-mass star formation, it is necessary to learn more about the physical conditions and stability in relatively unevolved IRDCs. Thus, for characterising IRDCs studies of large samples are needed. We investigate a complete sample of 218 northern hemisphere high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion transitions. We detected ammonia (1,1)-inversion transition lines in 109 of our IRDC candidates. Using the data we were able to study the physical conditions within the star-forming regions statistically. We compared them with the conditions in more evolved regions which have been observed in the same fashion as our sample sources. Our results show that IRDCs have, on average, rotation temperatures of 15 K, are turbulent (with line width FWHMs around 2 km s${}^{-1}$), have ammonia column densities on the order of $10^{14}$ cm${}^{-2}$ and molecular hydrogen column densities on the order of $10^{22}$ cm${}^{-2}$. Their virial masses are between 100 and a few 1000 M${}_{\odot }$. The comparison of bulk kinetic and potential energies indicate that the sources are close to virial equilibrium. IRDCs are on average cooler and less turbulent than a comparison sample of high-mass protostellar objects, and have lower ammonia column densities. Virial parameters indicate that the majority of IRDCs are currently stable, but are expected to collapse in the future.

21 pages, 11 figures, 7 tables. Paper accepted for publication in Astronomy & Astrophysics

References in corpus (4)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey
• Isolated starless cores in IRDCs in the Hi-GAL survey

Cited by in corpus (43)

• ATLASGAL --- towards a complete sample of massive star forming clumps
• The dynamical properties of dense filaments in the infrared dark cloud G035.39-00.33
• Chemical evolution in the early phases of massive star formation. I
• Far-Infrared Dust Temperatures and Column Densities of the MALT90 Molecular Clump Sample
• Distinct Chemical Regions in the "Prestellar" Infrared Dark Cloud (IRDC) G028.23-00.19
• VLA observations of ammonia in high-mass star formation regions
• Weak and Compact Radio Emission in Early High-Mass Star Forming Regions: I. VLA Observations
• GMC Collisions as Triggers of Star Formation. III. Density and Magnetically Regulated Star Formation
• Investigating the structure and fragmentation of a highly filamentary IRDC
• The SEDIGISM survey: Molecular clouds in the inner Galaxy
• Properties of dense cores in clustered massive star-forming regions at high angular resolution
• The Core Mass Function in the Massive Protocluster G286.21+0.17 revealed by ALMA
• Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: Cloud formation signatures and carbon gas fractions
• Outflow detection in a 70 $\mu$m dark high-mass core
• The RMS Survey: Ammonia mapping of the environment of massive young stellar objects
• Are Infrared Dark Clouds Really Quiescent?
• Temperature structure and kinematics of the IRDC G035.39-00.33
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde. III. The Orion Molecular Cloud 1
• The Giant Molecular Cloud Environments of Infrared Dark Clouds
• Kinetic temperature of massive star forming molecular clumps measured with formaldehyde. II. The Large Magellanic Cloud
• Physical Conditions of the Earliest Phases of Massive Star Formation: Single-Dish and Interferometric Observations of Ammonia and CCS in Infrared Dark Clouds
• Dynamical cloud formation traced by atomic and molecular gas
• ATLASGAL - Ammonia observations towards the southern Galactic Plane
• The Comparison of Physical Properties Derived from Gas and Dust in a Massive Star-Forming Region
• Thermal balance and comparison of gas and dust properties of dense clumps in the Hi-GAL survey
• The chemical structure of young high-mass star-forming clumps: (I) Deuteration
• Simultaneous Survey of Water and Class I Methanol Masers toward Red MSX Sources
• Interaction Between HII Region and AFGL333-Ridge: Implications to the Star Formation Scenario
• Kinematic and Thermal Structure at the onset of high-mass star formation
• Towards the impact of GMC collisions on the star formation rate
• Ammonia observations towards the Aquila Rift cloud complex
• A survey of SiO $J=$ 1 -- 0 emission toward massive star-forming regions
• The RMS Survey: Ammonia mapping of the environment of young massive stellar objects II
• Hyperfine Group Ratio: A Recipe for Deriving Kinetic Temperature from Ammonia Inversion Lines
• Observations of multiple NH${}_3$ transitions in W33
• The Seahorse Nebula: New views of the filamentary infrared dark cloud G304.74+01.32 from SABOCA, Herschel, and WISE
• Cloud-cloud collision and star formation in G013.313+0.193
• Inadequate turbulent support in low-metallicity molecular clouds
• Cyanopolyyne line survey towards high-mass star-forming regions with TMRT
• The Correlation of Dust and Gas Emission in Star-Forming Environments
• Synthetic ngVLA line observations of a massive star-forming cloud
• The effect of magnetic field morphology on the structure of massive IRDC clumps
• The TMRT K Band Observations towards 26 Infrared Dark Clouds: NH${}_3$, CCS, and HC${}_3$N