Cosmic rays, gas and dust in nearby anticentre clouds : I -- CO-to-H2 conversion factors and dust opacities

Abstract

We aim to explore the capabilities of dust emission and rays for probing the properties of the interstellar medium in the nearby anti-centre region, using gamma-ray observations with the Fermi Large Area Telescope (LAT), and the thermal dust optical depth inferred from Planck and IRAS observations. In particular, we aim at quantifying potential variations in cosmic-ray density and dust properties per gas nucleon across the different gas phases and different clouds, and at measuring the CO-to-H2 conversion factor, X${}_{CO}$ , in different environments. We have separated six nearby anti-centre clouds that are coherent in velocities and distances, from the Galactic-disc background in HI 21-cm and ${}^{12}$CO 2.6-mm line emission. We have jointly modelled the gamma-ray intensity recorded between 0.4 and 100 GeV, and the dust optical depth at 353 GHz as a combination of HI-bright, CO-bright, and ionised gas components. The complementary information from dust emission and gamma rays was used to reveal the gas not seen, or poorly traced, by HI , free-free, and ${}^{12}$CO emissions, namely (i) the opaque HI and diffuse H${}_2$ present in the Dark Neutral Medium at the atomic-molecular transition, and (ii) the dense H${}_2$ to be added where ${}^{12}$CO lines saturate. The measured interstellar gamma-ray spectra support a uniform penetration of the cosmic rays with energies above a few GeV through the clouds. We find a gradual increase in grain opacity as the gas becomes more dense. The increase reaches a factor of four to six in the cold molecular regions that are well shielded from stellar radiation. Consequently, the X${}_{CO}$ factor derived from dust is systematically larger by 30% to 130% than the gamma-ray estimate. We also evaluate the average gamma-ray X${}_{CO}$ factorfor each cloud, and find that X${}_{CO}$ tends to decrease from diffuse to more compact molecular clouds, as expected from theory.

References in corpus (67)

• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• Validation of the new Hipparcos reduction
• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results
• The CO-to-H2 Conversion Factor
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• Fermi Large Area Telescope Second Source Catalog
• Planck 2013 results. XI. All-sky model of thermal dust emission
• Fermi-LAT Observations of the Diffuse Gamma-Ray Emission: Implications for Cosmic Rays and the Interstellar Medium
• The Dark Molecular Gas
• The CO-to-H2 Conversion Factor and Dust-to-Gas Ratio on Kiloparsec Scales in Nearby Galaxies
• A Full-Sky H-alpha Template for Microwave Foreground Prediction
• The Fermi Large Area Telescope On Orbit: Event Classification, Instrument Response Functions, and Calibration
• A Three-Dimensional Map of Milky-Way Dust
• Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy
• The WISE Catalog of Galactic HII Regions
• Ultraviolet Survey of CO and H_2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
• The relation between gas and dust in the Taurus Molecular Cloud
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• The Optical-Infrared Extinction Curve and its Variation in the Milky Way
• Planck Early Results: Thermal dust in Nearby Molecular Clouds
• The GALFA-HI Survey: Data Release 1
• CO-dark gas and molecular filaments in Milky Way type galaxies
• Fermi observations of Cassiopeia and Cepheus: diffuse gamma-ray emission in the outer Galaxy
• GASS: The Parkes Galactic All-Sky Survey. II. Stray-Radiation Correction and Second Data Release
• The Effelsberg-Bonn HI Survey: Milky Way gas. First data release
• Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
• The Millennium Arecibo 21-cm Absorption Line Survey. I. Techniques and Gaussian Fits
• Planck intermediate results. XVII. Emission of dust in the diffuse interstellar medium from the far-infrared to microwave frequencies
• Modeling CO Emission: II. The Physical Characteristics that Determine the X factor in Galactic Molecular Clouds
• The California Molecular Cloud
• Changes Of Dust Opacity With Density in the Orion A Molecular Cloud
• Molecular line intensities as measures of cloud masses - I. Sensitivity of CO emissions to physical parameter variations
• The CO luminosity and CO-H2 conversion factor of diffuse ISM: does CO emission trace dense molecular gas?
• Evidence for Environmental Changes in the Submillimeter Dust Opacity
• Constraints on the Cosmic-Ray Density Gradient beyond the Solar Circle from Fermi gamma-ray Observations of the Third Galactic Quadrant
• Variation in dust properties in a dense filament of the Taurus molecular complex (L1506)
• Dark gas in the solar neighnorhood from extinction data
• Chemical probes of turbulence in the diffuse medium: the TDR model
• The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results
• Effects of magnetic fields on the cosmic-ray ionization of molecular cloud cores
• Structure Detection in Low Intensity X-Ray Images
• Fermi LAT study of cosmic-rays and the interstellar medium in nearby molecular clouds
• Evidence for dust evolution within the Taurus Complex from Spitzer images
• Gamma-rays from halos around stars and the Sun
• E(B-V), N(H I) and N(H_2)
• The cosmic-ray and gas content of the Cygnus region as measured in gamma rays by the Fermi Large Area Telescope
• Cosmic ray penetration in diffuse clouds
• Imaging diffuse clouds: Bright and dark gas mapped in CO
• A derivation of the free-free emission on the Galactic plane between l=20 and 44 degrees
• UV-driven chemistry in simulations of the interstellar medium. I. Post-processed chemistry with the Meudon PDR code
• The temperature of the diffuse HI in the Milky Way I: High resolution HI 21 cm absorption studies
• An HI column density threshold for cold gas formation in the Galaxy
• The CO-to-H2 Conversion Factor across the Perseus Molecular Cloud
• Dust Emission from the Perseus Molecular Cloud
• Fermi-LAT Observations of High- and Intermediate-Velocity Clouds: Tracing Cosmic Rays in the Halo of the Milky Way
• Gamma-ray observations of the Orion Molecular Clouds with the Fermi Large Area Telescope
• Dust-to-gas ratio, $X_{\mathrm{CO}}$ factor and CO-dark gas in the Galactic anticentre: an observational study
• EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6
• Planck intermediate results. XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck
• CMB reconstruction from the WMAP and Planck PR2 data
• Allsky NICER and NICEST extinction maps based on the 2MASS near-infrared survey
• Far-ultraviolet Observations of the Taurus-Perseus-Auriga Complex
• Synthetic observations of molecular clouds in a galactic center environment: I. Studying maps of column density and integrated intensity
• A High Galactic Latitude HI 21cm-line Absorption Survey using the GMRT: I. Observations and Spectra

Cited by in corpus (50)

• Science with e-ASTROGAM (A space mission for MeV-GeV gamma-ray astrophysics)
• Search for Spatial Extension in High-Latitude Sources Detected by the Fermi Large Area Telescope
• Dust, CO and [CI]: Cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time
• Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM
• The ISM scaling relations in DustPedia late-type galaxies: A benchmark study for the Local Universe
• The X_CO conversion factor from galactic multiphase ISM simulations
• Galactic halo size in the light of recent AMS-02 data
• The optical properties of dust: the effects of composition, size, and structure
• Central molecular zones in galaxies: 12CO-to-13CO ratios, carbon budget, and X factors
• Molecular Gas Properties and CO-to-H2 Conversion Factors in the Central Kiloparsec of NGC 3351
• The Physical Drivers and Observational Tracers of CO-to-H2 Conversion Factor Variations in Nearby Barred Galaxy Centers
• From grains to pebbles: the influence of size distribution and chemical composition on dust emission properties
• Low energy cosmic rays
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• 3D magnetic field morphology of the Perseus molecular cloud
• Optically thick HI does not dominate dark gas in the local ISM
• Molecular ion abundances in the diffuse ISM : CF+, HCO+, HOC+, and C3H+
• Dust continuum, CO, and [C I] 1-0 lines: self-consistent H2 mass estimates and the possibility of globally CO-dark galaxies at $z=0.35$
• Exploring the properties of warm and cold atomic hydrogen in the Taurus and Gemini regions
• Gas shells and magnetic fields in the Orion-Eridanus superbubble
• Galactic diffuse gamma-ray emission from GeV to PeV energies in light of up-to-date cosmic ray measurements
• Hard and bright gamma-ray emission at the base of the Fermi bubbles
• Cosmic-rays, gas, and dust in nearby anticentre clouds : II -- Interstellar phase transitions and the Dark Neutral Medium
• Gamma-Ray Emission from Molecular Clouds Generated by Penetrating Cosmic Rays
• CO-to-H${}_2$ Conversion and Spectral Column Density in Molecular Clouds: The Vriability of $X_{\mathrm{CO}}$ Factor
• Evidence of Cosmic-Ray Excess from Local Giant Molecular Clouds
• Reproducing the CO-to-H${}_2$ conversion factor in cosmological simulations of Milky Way-mass galaxies
• Deciphering Residual Emissions: Time-Dependent Models for the Non-Thermal Interstellar Radiation from the Milky Way
• Quantitative inference of the $H_2$ column densities from 3 mm molecular emission: A case study towards Orion B
• Cosmic-rays, gas, and dust in nearby anti-centre clouds : III -- Dust extinction, emission, and grain properties
• Revealing The CO X-factor In Dark Molecular Gas through Sensitive ALMA Absorption Observations
• A pilot search for extragalactic OH absorption with FAST
• Multiple emission components in the Cygnus cocoon detected from Fermi-LAT observations
• Fermi-LAT gamma-ray study of the interstellar medium and cosmic rays in the Chamaeleon Molecular-Cloud Complex: A look at the dark gas as optically thick HI
• The Astrochemical Impact of Cosmic Rays in Protoclusters II: CI-to-H${}_2$ and CO-to-H${}_2$ Conversion Factors
• Variations between Dust and Gas in the Diffuse Interstellar Medium. 3. Changes in Dust Properties
• SPLASH: The Southern Parkes Large-Area Survey in Hydroxyl -- Data Description & Release
• The CO-dark molecular gas in the cold HI arc
• Evidence for large-scale excesses associated with low HI column densities in the sky I. Dust excess
• The cosmic-ray content of the Orion-Eridanus superbubble
• Gas, dust, and the CO-to-molecular gas conversion factor in low-metallicity starbursts
• The Dark Neutral Medium is (Mostly) Molecular Hydrogen
• Signatures of Recent Cosmic-Ray Acceleration in the High-Latitude $\gamma$-Ray Sky
• 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
• Probing local cosmic rays using Fermi-LAT observation of a mid-latitude region in the third Galactic quadrant
• Study of the Cosmic Rays and Interstellar Medium in Local HI Clouds using Fermi-LAT Gamma-Ray Observations
• Cosmic rays, gas and dust in the Central Molecular Zone I -- $X_{CO}$ factors, cosmic-ray densities and dust opacities
• A three-dimensional reconstruction of the interstellar magnetic field toward a star-forming region
• The MACH HI absorption survey I: Physical conditions of cold atomic gas outside of the Galactic plane
• Measurement of Cosmic-Ray Density in the Spiral Arms toward Galactic Anticenter