The Probability Distribution Function of Gas Surface Density in M33

Abstract

The probability distribution functions (PDFs) for atomic, molecular, and total gas surface densities of M33 are determined at a resolution of about 50~pc over regions that share coherent morphological properties to unveil fingerprints of self-gravity across the star-forming disk. Most of the total gas PDFs from the central region to the edge of the star-forming disk are well-fitted by log-normal functions whose width decreases radially outwards. Because the HI velocity dispersion is approximately constant across the disk, the decrease of the PDF width is consistent with a lower Mach number for the turbulent ISM at large galactocentric radii where a higher fraction of HI is in the warm phase. The atomic gas is found mostly at face-on column densities below N${}_H^{lim}$=2.5 10${}^{21}$~cm${}^{-2}$, with small radial variations of N${}_H^{lim}$. The molecular gas PDFs do not show strong deviations from log-normal functions in the central region where molecular fractions are high. Here the high pressure and rate of star formation shapes the PDF as a log-normal function dispersing self-gravitating complexes with intense feedback at all column densities that are spatially resolved. Power law PDFs for the molecules are found near and above N${}_H^{lim}$, in the well defined southern spiral arm and in a continuous dense filament extending at larger galactocentric radii; this is evident in cloud samples at different evolutionary stages along the star formation cycle. In the filament nearly half of the molecular gas departs from a log-normal PDF and power laws are also observed in pre-star forming molecular complexes. The slope of the power law is between -1 and -2. This slope, combined with maps showing where the different parts of the power law PDFs come from, suggest a power-law stratification of density within molecular cloud complexes, which is consistent with the dominance of self-gravity.

12 pages, 8 figures, accepted for publication in A&A

References in corpus (25)

• Theory of Star Formation
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• What is Driving the HI Velocity Dispersion?
• 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
• Rapid Molecular Cloud and Star Formation: Mechanisms and Movies
• A Wide-field High Resolution HI Mosaic of Messier 31: I. Opaque Atomic Gas and Star Formation Rate Density
• Molecular clouds have power-law probability distribution functions
• Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure
• Star formation in M33: multiwavelength signatures across the disk
• The ISM in spiral galaxies: can cooling in spiral shocks produce molecular clouds?
• Particularly Efficient Star Formation in M33
• Understanding star formation in molecular clouds II. Signatures of gravitational collapse of IRDCs
• Dynamical signatures of a LCDM-halo and the distribution of the baryons in M33
• The shapes of column density PDFs - The importance of the last closed contour
• The ALMA view of GMCs in NGC 300: Physical Properties and Scaling Relations at 10 pc Resolution
• The young star cluster population of M51 with LEGUS - II. Testing environmental dependencies
• On the Appearance of Thresholds in the Dynamical Model of Star Formation
• Properties and rotation of molecular clouds in M 33
• Eventful Evolution of Giant Molecular Clouds in Dynamically Evolving Spiral Arms
• Simulations of the flocculent spiral M33: what drives the spiral structure?
• Spatial distribution of star formation related to ionized regions throughout the inner Galactic plane
• A statistical study of giant molecular clouds traced by ${}^{13}$CO, C${}^{18}$O, CS, and CH${}_3$OH in the disk of NGC 1068 based on ALMA observations
• The molecular gas mass of M33
• Bipolar H{\sc ii} regions produced by cloud/cloud collisions

Cited by in corpus (14)

• Simulations of the star-forming molecular gas in an interacting M51-like galaxy
• The Self-gravitating Gas Fraction and The Critical Density for Star Formation
• SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
• The Resolved Distributions of Dust Mass and Temperature in Local Group Galaxies
• Two Thresholds for Globular Cluster Formation and their Dominance of Star Formation in the Early-Universe
• The structure and characteristic scales of molecular clouds
• Dense Gas in a Giant Molecular Filament
• Rise and fall of molecular clouds across the M33 disk
• A High-Resolution, Dust-Selected Molecular Cloud Catalogue of M33, the Triangulum Galaxy
• A Synergy of the Velocity Gradients Technique and the Probability Density Functions for Identifying Gravitational Collapse in Self-Absorbing Media
• Star formation drivers across the M33 disk
• Molecular cloud matching in CO and dust in M33 II. Physical properties of giant molecular clouds
• Quantitative Morphology of Galactic Cirrus in Deep Optical Imaging
• Description of turbulent dynamics in the interstellar medium: Multifractal microcanonical analysis: II. Sparse filtering of Herschel observation maps and visualization of filamentary structures at different length scales