CO mapping of Cygnus-X -- volume density distribution

Abstract

We present CO(2-1) and ${}^{13}$CO(2-1) maps of the Cygnus-X molecular cloud complex using the 10m Heinrich Hertz Submillimeter Telescope (SMT). The maps cover the southern portion of the complex which is strongly impacted by the feedback from the Cygnus OB2 association. Combining CO(1-0) and ${}^{13}$CO(1-0) maps from the Nobeyama 45m Cygnus-X CO Survey, we carry out a multi-transition molecular line analysis with RADEX and derive the volume density of velocity-coherent gas components. We select those components with a column density in the power-law tail part of the column density probability distribution function (N-PDF) and assemble their volume density into a volume density PDF ($\rho$-PDF). The $\rho$-PDF exhibits a power-law shape in the range of 10${}^{4.5}$ cm${}^{-3}$ $\lesssim n_{{\mathrm{H}}_2}\lesssim$ 10${}^{5.5}$ cm${}^{-3}$ with a fitted slope of $\alpha =-1.12\pm 0.05$. The slope is shallower than what is predicted by simulations of rotationally supported structures or those undergoing gravitational collapse. Applying the same analysis to synthetic observations with feedback may help identify the cause of the shallow slope. The $\rho$-PDF provides another useful benchmark for testing models of molecular cloud formation and evolution.

arXiv comment16 pages, 9 figures, accepted by ApJ

References in corpus (46)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• A computer program for fast non-LTE analysis of interstellar line spectra
• Structural Analysis of Molecular Clouds: Dendrograms
• The Universality of the Stellar IMF
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• The Star Formation Rate of Supersonic MHD Turbulence
• Probing the evolution of molecular cloud structure: From quiescence to birth
• How to Calculate Molecular Column Density
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• Density probability distribution in one-dimensional polytropic gas dynamics
• Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region
• On the universality of supersonic turbulence
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• On the Density Distribution in Star-forming Interstellar Clouds
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• Gravity or turbulence? II. Evolving column density PDFs in molecular clouds
• Modelling CO formation in the turbulent interstellar medium
• On the evolution of the density pdf in strongly self-gravitating systems
• The Massive Star Population of Cygnus OB2
• Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds
• Evolution of column density distributions within Orion~A
• Detection of two power-law tails in the probability distribution functions of massive GMCs
• Ionization compression impact on dense gas distribution and star formation, Probability density functions around H ii regions as seen by Herschel
• Density Probability Distribution Functions in Supersonic Hydrodynamic and MHD Turbulence
• Star Formation in Self-Gravitating Turbulent Fluids
• A Spitzer View of Star Formation in the Cygnus X North Complex
• Understanding star formation in molecular clouds III. Probability distribution functions of molecular lines in Cygnus X
• The Structure of Molecular Clouds: II - Column Density and Mass Distributions
• Evidence that 1I/2017 U1 (`Oumuamua) was composed of molecular hydrogen ice
• Mass and Magnetic distributions in Self Gravitating Super Alfvenic Turbulence with AMR
• A $Herschel-SPIRE$ Survey of the Mon R2 Giant Molecular Cloud: Analysis of the Gas Column Density Probability Density Function
• Understanding star formation in molecular clouds IV. Column density PDFs from quiescent to massive molecular clouds
• The Dependence of Protostellar Luminosity on Environment in the Cygnus-X Star-Forming Complex
• The Relationship Between the Dust and Gas-Phase CO Across the California Molecular Cloud
• Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function
• Enhanced Core Formation Rate in a Turbulent Cloud by Self-gravity
• JCMT HARP CO 3-2 Observations of Molecular Outflows in W5
• Evolution of the density PDF in star forming clouds: the role of gravity
• The density structure of supersonic self-gravitating turbulence
• Dense Gas in a Giant Molecular Filament
• Nobeyama 45-m Cygnus X CO Survey: II Physical Properties of ${\mathrm{C}}^{18}\mathrm{O}$ Clumps
• Probing the Cold Deep Depths of the California Molecular Cloud: The Icy Relationship between CO and Dust
• Nobeyama 45m Cygnus-X CO survey I: photodissociation of molecules revealed by the unbiased large-scale CN and C${}^{18}$O maps
• Multi log-normal density structure in Cygnus-X molecular clouds: A fitting for N-PDF without power-law