CO-dark gas and molecular filaments in Milky Way type galaxies

Abstract

We use the moving mesh code AREPO coupled to a time-dependent chemical network to investigate the formation and destruction of molecular gas in simulated spiral galaxies. This allows us to determine the characteristics of the gas that is not traced by CO emission. Our extremely high resolution AREPO simulations allow us to capture the chemical evolution of the disc, without recourse to a parameterised `clumping factor'. We calculate H2 and CO column densities through our simulated disc galaxies, and estimate the CO emission and CO-H2 conversion factor. We find that in conditions akin to those in the local interstellar medium, around 42% of the total molecular mass should be in CO-dark regions, in reasonable agreement with observational estimates. This fraction is almost insensitive to the CO integrated intensity threshold used to discriminate between CO-bright and CO-dark gas, as long as this threshold is less than 10 K km/s. The CO-dark molecular gas primarily resides in extremely long (>100 pc) filaments that are stretched between spiral arms by galactic shear. Only the centres of these filaments are bright in CO, suggesting that filamentary molecular clouds observed in the Milky Way may only be small parts of much larger structures. The CO-dark molecular gas mainly exists in a partially molecular phase which accounts for a significant fraction of the total disc mass budget. The dark gas fraction is higher in simulations with higher ambient UV fields or lower surface densities, implying that external galaxies with these conditions might have a greater proportion of dark gas.

Accepted by MNRAS

References in corpus (12)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• Ultraviolet Survey of CO and H_2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• The Spitzer Survey of the Small Magellanic Cloud: FIR Emission and Cold Gas in the SMC
• Abundances and Behavior of 12CO, 13CO, and C2 in Translucent Sight Lines
• Direct Measurement of the Ratio of Carbon Monoxide to Molecular Hydrogen in the Diffuse Interstellar Medium
• Six Myths on the Virial Theorem for Interstellar Clouds
• Spurs and feathering in spiral galaxies
• The ISM in spiral galaxies: can cooling in spiral shocks produce molecular clouds?
• Chemical Rates on Small Grains and PAHs: C^+ Recombination and H_2 Formation

Cited by in corpus (82)

• On the nature of star-forming filaments: I. Filament morphologies
• Photodissociation and X-Ray Dominated Regions
• Large-scale filaments associated with Milky Way spiral arms
• The Bones of the Milky Way
• Giant Molecular Cloud Catalogues for PHANGS-ALMA: Methods and Initial Results
• The origin of fast molecular outflows in quasars: molecule formation in AGN-driven galactic winds
• 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
• The Cloud Factory I: Generating resolved filamentary molecular clouds from galactic-scale forces
• Simulations of the star-forming molecular gas in an interacting M51-like galaxy
• The Hi-GAL catalogue of dusty filamentary structures in the Galactic Plane
• Discovery of a Perseus-like cloud in the early Universe: HI-to-H2 transition, carbon monoxide and small dust grains at zabs=2.53 towards the quasar J0000+0048
• A Census of Large-Scale ($\ge$ 10 pc), Velocity-Coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree
• The structure and statistics of interstellar turbulence
• CO-dark molecular gas at high redshift: very large H${}_2$ content and high pressure in a low metallicity damped Lyman-alpha system
• Cold and warm atomic gas around the Perseus molecular cloud I: Basic Properties
• Metallicity dependence of the H/H${}_2$ and C${}^{+}$/C/CO distributions in a resolved self-regulating interstellar medium
• Lighting the dark molecular gas: H${}_2$ as a direct tracer
• The Interstellar Medium and star formation on kpc size scales
• Understanding star formation in molecular clouds IV. Column density PDFs from quiescent to massive molecular clouds
• Photochemistry and Heating/Cooling of the Multiphase Interstellar Medium with UV Radiative Transfer for Magnetohydrodynamic Simulations
• Photodissociation Region Diagnostics Across Galactic Environments
• The Physical Drivers and Observational Tracers of CO-to-H2 Conversion Factor Variations in Nearby Barred Galaxy Centers
• The dense gas mass fraction in the W51 cloud and its protoclusters
• CO-dark gas and molecular filaments in Milky Way-type galaxies - II: The temperature distribution of the gas
• CO excitation, molecular gas density and interstellar radiation field in local and high-redshift galaxies
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Fermi-LAT Observations of High- and Intermediate-Velocity Clouds: Tracing Cosmic Rays in the Halo of the Milky Way
• Carbon and hydrogen radio recombination lines from the cold clouds towards Cassiopeia A
• Synthetic CO, H2 and HI surveys of the Galactic 2nd Quadrant, and the properties of molecular gas
• PHANGS-JWST First Results: The Dust Filament Network of NGC 628 and its Relation to Star Formation Activity
• PHANGS--JWST First Results: ISM structure on the turbulent Jeans scale in four disk galaxies observed by JWST and ALMA
• Star Formation and Molecular Gas Diagnostics with Mid- and Far-Infrared Emission
• Recovering interstellar gas properties with HI spectral lines: A comparison between synthetic spectra and 21-SPONGE
• A new approach to determine optically thick H2 cooling and its effect on primordial star formation
• Simulating the atomic and molecular content of molecular clouds using probability distributions of physical parameters
• On the gamma-ray emission of W44 and its surroundings
• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. I. Overview: CO Cloud Distributions
• Comparing the Properties of GMCs in M33 from Simulations and Observations
• How Cosmic Rays Mediate the Evolution of the Interstellar Medium
• A multi-wavelength observation and investigation of six infrared dark clouds
• The organization of cloud-scale gas density structure: high resolution CO vs. 3.6 $\mu$m brightness contrasts in nearby galaxies
• The Galactic Census of High- and Medium-mass Protostars. III ${}^{12}$CO Maps and Physical Properties of Dense Clump Envelopes and their Embedding GMCs
• Observations of neutral carbon in 29 high-z lensed dusty star forming galaxies and the comparison of gas mass tracers
• Synthetic Large-Scale Galactic Filaments -- on their Formation, Physical Properties, and Resemblance to Observations
• PHANGS-MeerKAT and MHONGOOSE HI observations of nearby spiral galaxies: physical drivers of the molecular gas fraction, $R_{\mathrm{mol}}$
• Atomic and molecular gas properties during cloud formation
• Revealing a spiral-shaped molecular cloud in our galaxy - Cloud fragmentation under rotation and gravity
• A Kpc Scale Molecular Wave in the Inner Galaxy: Feather of the Milky Way?
• Large-scale Velocity-coherent Filaments in the SEDIGISM Survey: Association with Spiral Arms and Fraction of Dense Gas
• Galactic coronae in Milky Way-like galaxies: the role of stellar feedback in gas accretion
• The "Maggie" filament: Physical properties of a giant atomic cloud
• The Cloud Factory II: Gravoturbulent Kinematics of Resolved Molecular Clouds in a Galactic Potential
• VERTICO V: The environmentally driven evolution of the inner cold gas discs of Virgo cluster galaxies
• Global enhancement and structure formation of the magnetic field in spiral galaxies
• Gas and Dust Properties in the Chamaeleon Molecular Cloud Complex based on the Optically Thick HI
• On the distribution of the Cold Neutral Medium in galaxy discs
• Emergence of high-mass stars in complex fiber networks (EMERGE). I. Early ALMA Survey: observations and massive data reduction
• The evolution of HCO${}^{+}$ in molecular clouds using a novel chemical post-processing algorithm
• Quantifying the Interstellar Medium and Cosmic Rays in the MBM 53, 54, and 55 Molecular Clouds and the Pegasus Loop using Fermi-LAT Gamma-ray Observations
• The discovery of the largest gas filament in our Galaxy, or a new spiral arm?
• An off-centred bulge or a satellite? Hydrodynamical $N$-body simulations of the disc galaxy NGC 5474
• Metallicity dependence of the CO-to-H${}_2$ and the [CI]-to-H${}_2$ conversion factors in galaxies
• A SOFIA Survey of [CII] in the galaxy M51 II. [CII] and CO kinematics across spiral arms
• HYACINTH: HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations
• Physical Properties and Scaling Relations of Molecular Clouds: the Impact of Star Formation
• The Cassiopeia Filament: A Blown Spur of the Local Arm
• Ionized carbon around IRC +10216
• Gas and Cosmic-Ray Properties in the MBM 53, 54, and 55 Molecular Clouds and the Pegasus Loop as Revealed by HI Line Profiles, Dust, and Gamma-Ray Data
• A Comprehensive All-Sky Catalog of 3345 Molecular Clouds from Three-dimensional Dust Extinction
• The Noctua Suite of Simulations -- The Difficulty of Growing Massive Black Holes in Low-Mass Dwarf Galaxies
• A deep-learning approach to the 3D reconstruction of dust density and temperature in star-forming regions
• Decaying turbulence in molecular clouds: how does it affect filament networks and star formation?
• Filament Formation via Collision-induced Magnetic Reconnection -- Formation of a Star Cluster
• Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size-Linewidth Relationship
• "Dust Giant": Extended and Clumpy Star-Formation in a Massive Dusty Galaxy at $z=1.38$
• Early Science with the Large Millimeter Telescope: discovery of the 12CO(1-0) emission line in the ring galaxy, VIIZw466
• Study of the Cosmic Rays and Interstellar Medium in Local HI Clouds using Fermi-LAT Gamma-Ray Observations
• Physical conditions in the gas phases of the giant HII region LMC-N11: II. Origin of [CII] and fraction of CO-dark gas
• Cold atomic gas identified by HI self-absorption. Cold atomic clouds toward giant molecular filaments
• Anisotropy in the carbon monoxide (CO) line emission across the Milky Way's disk
• Why most molecular clouds are gravitationally dominated
• CO Structures with Narrow Lines in Nearby Quiescent Regions