On column density thresholds and the star formation rate

Abstract

We present the results of a numerical study designed to address the question of whether there is a column density threshold for star formation within molecular clouds. We have simulated a large number of different clouds, with volume and column densities spanning a wide range of different values, using a state-of-the-art model for the coupled chemical, thermal and dynamical evolution of the gas. We show that star formation is only possible in regions where the mean (area-averaged) column density exceeds $10^{21}\mathrm{c}{\mathrm{m}}^{-2}$. Within the clouds, we also show that there is a good correlation between the mass of gas above a K-band extinction $A_{\mathrm{K}}=0.8$ and the star formation rate (SFR), in agreement with recent observational work. Previously, this relationship has been explained in terms of a correlation between the SFR and the mass in dense gas. However, we find that this correlation is weaker and more time-dependent than that between the SFR and the column density. In support of previous studies, we argue that dust shielding is the key process: the true correlation is one between the SFR and the mass in cold, well-shielded gas, and the latter correlates better with the column density than the volume density.

21 pages and 12 figures. Accepted for publication in MNRAS

References in corpus (20)

• Slow Star Formation in Dense Gas: Evidence and Implications
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• On the Density Distribution in Star-forming Interstellar Clouds
• From the warm magnetized atomic medium to molecular clouds
• Equilibrium Star Cluster Formation
• The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows
• The effect of magnetic fields on star cluster formation
• The ISM in spiral galaxies: can cooling in spiral shocks produce molecular clouds?
• Massive stars in massive clusters IV: Disruption of clouds by momentum-driven winds
• The Nature of the Velocity Field in Molecular Clouds. I. The Non-Magnetic Case
• The Ionization Fraction of Barnard 68: Implications for Star and Planet Formation
• Indications of a sub-linear and non-universal Kennicutt-Schmidt relationship
• On the enhanced cosmic-ray ionization rate in the diffuse cloud towards Zeta Persei
• The Dynamical State fo the Starless Dense Core FeSt 1-457: A Pulsating Globule?
• The Dynamical State of the Starless Dense Core FeSt 1-457: A Pulsating Globule?
• The Milky Way as a Star Formation Engine

Cited by in corpus (47)

• The modelling of feedback in star formation simulations
• A Model for the Onset of Self-gravitation and Star Formation in Molecular Gas Governed by Galactic Forces: I. Cloud-scale Gas Motions
• Gravitational contraction versus Supernova driving and the origin of the velocity dispersion-size relation in molecular clouds
• Positive and negative feedback of AGN outflows in NGC 5728
• Tree-based solvers for adaptive mesh refinement code FLASH - I: gravity and optical depths
• Physical Processes in Star Formation
• SILCC-Zoom: H${}_2$ and CO-dark gas in molecular clouds -- The impact of feedback and magnetic fields
• On The Nature of Variations in the Measured Star Formation Efficiency of Molecular Clouds
• Dancing in the Dark: Uncertainty in ultra-faint dwarf galaxy predictions from cosmological simulations
• Interpreting the Star Formation Efficiency of Molecular Clouds with Ionising Feedback
• Simulating Star Clusters Across Cosmic Time: I. Initial Mass Function, Star Formation Rates and Efficiencies
• The HI-to-H2 Transition in a Turbulent Medium
• Helical Magnetic Fields in Molecular Clouds? A New Method to Determine the Line-of-Sight Magnetic Field Structure in Molecular Clouds
• Using CO line ratios to trace the physical properties of molecular clouds
• Star-Gas Surface Density Correlations in Twelve Nearby Molecular Clouds I: Data Collection and Star-Sampled Analysis
• Does the CO-to-H2 conversion factor depend on the star formation rate?
• Star-formation rates from young-star counts and the structure of the ISM across the NGC346/N66 complex in the SMC
• The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds
• A model for the onset of self-gravitation and star formation in molecular gas governed by galactic forces: II. the bottleneck to collapse set by cloud-environment decoupling
• The First Stars: formation under X-ray feedback
• Thermal balance and comparison of gas and dust properties of dense clumps in the Hi-GAL survey
• PDFchem: A new fast method to determine ISM properties and infer environmental parameters using probability distributions
• Very Thin Disc Galaxies in The SDSS Catalog of Edge-on Galaxies
• How galactic environment regulates star formation
• BST1047+1156: An extremely diffuse and gas-rich object in the Leo I Group
• High star formation rates in turbulent atomic-dominated gas in the interacting galaxies IC 2163 and NGC 2207
• The Parsec-Scale Relationship Between I_CO and A_V in Local Molecular Clouds
• Molecular Emission in Dense Massive Clumps from the Star-Forming Regions S231-S235
• Stellar and Gaseous Disk Structures in Cosmological Galaxy Equilibrium Models
• Molecular cloud formation as seen in synthetic Hi and molecular gas observations
• Tracing young star-forming clumps in the nearby flocculent spiral galaxy NGC 7793 with UVIT imaging
• Determining Star Formation Thresholds from Observations
• The Column Densities of Molecular Gas across Cosmic Time: Bridging Observations and Simulations
• Testing the star formation scaling relations in the clumps of the North American and Pelican cloud complexes
• Carina's Pillars of Destruction: the view from ALMA
• Rethinking a Mysterious Molecular Cloud
• Continuum Observations of M51 and M83 at 1.1 mm with AzTEC
• Non-Equilibrium Abundances Treated Holistically (NEATH): the molecular composition of star-forming clouds
• The CARMA-NRO Orion Survey: Filament Formation via Collision-Induced Magnetic Reconnection -- The Stick in Orion A
• Characterization of dense Planck clumps observed with Herschel and SCUBA-2
• Implementing Dust Shielding as a Criteria for Star Formation
• The CARMA-NRO Orion Survey: Core Emergence and Kinematics in the Orion A Cloud
• Star and Cluster Formation in the Sh2-112 Filamentary Cloud Complex
• Gravity or turbulence? VII. The Schmidt-Kennicutt law, the star formation efficiency, and the mass density of clusters from gravitational collapse rather than turbulent support
• Line emission from filaments in molecular clouds
• Atomic and Molecular Phases of the Interstellar Medium
• Comparison of Herschel and ArTéMiS observations of massive filaments