Planck intermediate results. XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck

Abstract

Shortened abstract: Observations of the nearby Chamaeleon clouds in gamma rays with the Fermi Large Area Telescope and in thermal dust emission with Planck and IRAS have been used with the HI and CO radio data to (i) map the gas column densities in the different phases and at the dark neutral medium (DNM) transition between the HI-bright and CO-bright media; (ii) constrain the CO-to-$H_2$ conversion factor, $X_{CO}$; (iii) probe the dust properties per gas nucleon in each gas phase and spatially across the clouds. We have separated clouds in velocity in HI and CO emission and modelled the 0.4-100 GeV intensity, the dust optical depth at 353 GHz, the thermal radiance of the large grains, and an estimate of the dust extinction empirically corrected for the starlight intensity, $A_{VQ}$. The gamma-ray emissivity spectra confirm that the GeV-TeV cosmic rays uniformly permeate all gas phases up to the CO cores. The dust and cosmic rays reveal large amounts of DNM gas, with comparable spatial distributions and twice as much mass as in the CO-bright clouds. We give constraints on the HI-DNM-CO transitions and CO-dark $H_2$ fractions for separate clouds. The corrected extinction provides the best fit to the total gas traced by the gamma rays, but we find evidence for a rise in $A_{VQ}/N_H$ and a steep rise in opacity, with increasing $N_H$ and $H_2$ fraction, and with decreasing dust temperature. We observe less variations for the specific power of the grains, except for a decline by half in the CO cores. This combined information suggests grain evolution. The gamma rays and dust radiance yield consistent $X_{CO}$ estimates near $0.7\times 10^{20}$ cm${}^{-2}$ (K km/s)${}^{-1}$. The other dust tracers yield biased values because of the grain opacity rise in the CO clouds. These results also confirm a factor of 2 difference between $X_{CO}$ estimates at pc and kpc scales.

32 pages, 23 figures, accepted for publication in A&A

References in corpus (7)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The Atomic to Molecular Transition in Galaxies. II: HI and H_2 Column Densities
• The Spectrum and Morphology of the Fermi Bubbles
• 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
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry

Cited by in corpus (25)

• Planck intermediate results. XXIX. All-sky dust modelling with Planck, IRAS, and WISE observations
• A new, large-scale map of interstellar reddening derived from HI emission
• Evolution of OH and CO-dark Molecular Gas Fraction Across a Molecular Cloud Boundary In Taurus
• Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM
• SILCC-Zoom: H${}_2$ and CO-dark gas in molecular clouds -- The impact of feedback and magnetic fields
• The Denoised, Deconvolved, and Decomposed Fermi $\gamma$-ray sky - An application of the D${}^3$PO algorithm
• Cosmic rays, gas and dust in nearby anticentre clouds : I -- CO-to-H2 conversion factors and dust opacities
• The Three-Dimensional Spatial Distribution of Interstellar Gas in the Milky Way: Implications for Cosmic Rays and High-Energy Gamma-Ray Emissions
• Planck intermediate results. XLVIII. Disentangling Galactic dust emission and cosmic infrared background anisotropies
• Gamma-ray Astrophysics in the MeV Range: the ASTROGAM Concept and Beyond
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Interpreting Flux from Broadband Photometry
• Close-up view of a luminous star-forming galaxy at z=2.95
• Cosmic-rays, gas, and dust in nearby anticentre clouds : II -- Interstellar phase transitions and the Dark Neutral Medium
• Kinetic Tomography I: A Method for Mapping the Milky Way's Interstellar Medium in Four Dimensions
• A catalog of 1.5273 micron diffuse interstellar bands based on APOGEE hot telluric calibrators
• Constraining the Distance to the North Polar Spur with Gaia DR2
• CO-to-H${}_2$ Conversion and Spectral Column Density in Molecular Clouds: The Vriability of $X_{\mathrm{CO}}$ Factor
• Standing in the shadow of dark gas: ALMA observations of absorption from dark CO in the molecular DNM of Chamaeleon
• Molecular Gas and Dark Neutral Medium in the Outskirts of Chamaeleon
• The comoving mass density of MgII from $z\sim 2$ to $5.5$
• Gas and Dust Properties in the Chamaeleon Molecular Cloud Complex based on the Optically Thick HI
• The Star-Formation Properties of the Observed and Simulated AGN Universe: BAT vs EAGLE
• Probing local cosmic rays using Fermi-LAT observation of a mid-latitude region in the third Galactic quadrant
• Investigation of cosmic ray penetration with wavelet cross-correlation analysis