The Central 300 pc of the Galaxy probed by infrared spectra of H${}_3^{+}$ and CO: part I. Predominance of warm and diffuse gas and high H${}_2$ ionization rate

Abstract

The molecular gas in the Central Molecular Zone (CMZ) of the Galaxy has been studied using infrared absorption spectra of H${}_3^{+}$ lines at 3.5-4.0 $\mu$m and CO lines near 2.34 $\mu$m. In addition to the previously reported spectra of these lines toward 8 stars located within 30 pc of Sgr A${}^{\ast }$, there are now spectra toward $\sim$30 bright stars located from 140 pc west to 120 pc east of Sgr A${}^{\ast }$. The spectra show the presence of warm ($T\sim 200$ K) and diffuse ($n<100$cm${}^{-3}$) gas with $N$(H${}_3^{+}$) $\sim 3\times 10^{15}$cm${}^{-2}$ on majority of sightlines. Instead of our previous analysis in which only electrons from photoionization of carbon atoms were considered, we have developed a simple model calculation in which the cosmic ray ionization of H${}_2$ and H are also taken into account. We conclude: (1) Warm and diffuse gas dominates the volume of the CMZ. The volume filling factor of dense gas must be much less than 0.1 and the CMZ is not as opaque as previously considered. The X-ray emitting ultra-hot 10${}^8$K plasma, which some thought to dominate the CMZ, does not exist over extended regions. (2) The cosmic ray ionization rate is $\zeta \sim 2\times 10^{-14}$s${}^{-1}$, higher than in Galactic dense clouds and diffuse clouds by factors of $\sim$1000 and $\sim$100, respectively. If the equipartition law stands, this suggests a pervading magnetic field on the order of $\sim$100 $\mu$G.

arXiv comment39 pages, 7 tables, 10 figures, published at the ApJ

References in corpus (91)

• Abundance Gradients and the Formation of the Milky Way
• A model for atomic and molecular interstellar gas: The Meudon PDR code
• The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• A 100-parsec elliptical and twisted ring of cold and dense molecular clouds revealed by Herschel around the Galactic Center
• Enhanced cosmic-ray flux toward zeta Persei inferred from laboratory study of H3+ - e- recombination rate
• A FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds
• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate
• Line derived infrared extinction towards the Galactic Center
• Interstellar Carbon in Translucent Sightlines
• Dense gas in the Galactic central molecular zone is warm and heated by turbulence
• Discrete sources as the origin of the Galactic X-ray ridge emission
• The largest oxigen bearing organic molecule repository
• Diffuse X-ray Emission in a Deep Chandra Image of the Galactic Center
• Radiative recombination data for modelling dynamic finite-density plasmas
• Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+
• A Deep Chandra Catalog of X-ray Point Sources toward the Galactic Center
• Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines
• A cosmic-ray dominated ISM in Ultra Luminous Infrared Galaxies: new initial conditions for star formation
• The ages of young star clusters, massive blue stragglers and the upper mass limit of stars: analysing age dependent stellar mass functions
• The thermal state of molecular clouds in the Galactic Center: evidence for non-photon-driven heating
• Carbon and Oxygen Galactic Gradients: Observational Values from HII Region Recombination Lines
• The massive star initial mass function of the Arches cluster
• Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High Energy Emission from the Inner 2deg by 1deg of the Galactic Center
• Ubiquitous argonium (ArH${}^{+}$) in the diffuse interstellar medium -- a molecular tracer of almost purely atomic gas
• Observations of H3+ in the Diffuse Interstellar Medium
• Complex organic molecules in the Galactic Centre: the N-bearing family
• Comparative study of CH+ and SH+ absorption lines observed towards distant star-forming regions
• The Origin of Diffuse X-ray and $\gamma$-ray Emission from the Galactic Center Region: Cosmic Ray Particles
• The Bolocam Galactic Plane Survey IV: 1.1 and 0.35 mm Dust Continuum Emission in the Galactic Center Region
• Evidence for a Weak Galactic Center Magnetic Field from Diffuse Low Frequency Nonthermal Radio Emission
• Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center
• The AST/RO Survey of the Galactic Center Region. I. The Inner 3 Degrees
• Chandra Deep X-ray Observation of a Typical Galactic Plane Region and Near-Infrared Identification
• The Survey of Water and Ammonia in the Galactic Center (SWAG): Molecular Cloud Evolution in the Central Molecular Zone
• Absorption Line Survey of H3+ toward the Galactic Center Sources II. Eight Infrared Sources within 30 pc of the Galactic Center
• Is H3+ cooling ever important in primordial gas?
• Origin of the Hard X-ray Emission from the Galactic Plane
• The dynamical evolution of molecular clouds near the Galactic Centre - II. Spatial structure and kinematics of simulated clouds
• A theoretical explanation for the Central Molecular Zone asymmetry
• Physical conditions in the central molecular zone inferred by H3+
• Point Sources from a Spitzer IRAC Survey of the Galactic Center
• Galactocentric variation of the gas-to-dust ratio and its relation with metallicity
• Warm H2 in the Galactic center region
• Detection of Widespread Hot Ammonia in the Galactic Center
• New method to study ion-molecule reactions at low temperatures and application to the H${}_2^{+}$ + H${}_2$ $\to$ H${}_3^{+}$ + H reaction
• Far-Infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near SgrA*
• Absorption Line Survey of H3+ toward the Galactic Center Sources I. GCS 3-2 and GC IRS3
• L- and M-band imaging observations of the Galactic Center region
• The Dense Gas Fraction in Galactic Center Clouds
• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• A survey of the Galactic center region in HCO+, H13CO+ and SiO
• Spectral imaging of the Central Molecular Zone in multiple 7-mm molecular lines
• Equipartition and Cosmic Ray Energy Densities in Central Molecular Zones of Starbursts
• Resonant structure of low-energy H3+ dissociative recombination
• The Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function
• Water Vapor around Sgr B2
• Turbulent Origin of the Galactic-Center Magnetic Field: Nonthermal Radio Filaments
• The Interstellar Medium of IRAS 08572+3915 NW: H3+ and Warm High Velocity CO
• Two New and Remarkable Sightlines through the Galactic Center's Molecular Gas
• Interstellar Extinction and Long-Period Variables in the Galactic Center
• Young massive stars in the ISOGAL survey II. The catalogue of bright YSO candidates
• Mapping photodissociation and shocks in the vicinity of Sgr A*
• The Quintuplet Cluster II. Analysis of the WN stars
• The start of the Sagittarius spiral arm (Sagittarius origin) and the start of the Norma spiral arm (Norma origin) - model-computed and observed arm tangents at galactic longitudes -20 degrees < l < +23 degrees
• The detection of the (J,K)=(18,18) line of NH3
• Scale heights and equivalent widths of the iron K-shell lines in the Galactic diffuse X-ray emission
• 3 mm spectral line survey of two lines of sight toward two typical cloud complexes in the Galactic Center
• Absorption Line Survey of H3+ toward the Galactic Center Sources III. Extent of the Warm and Diffuse Clouds
• Tracing the sources of cosmic rays with molecular ions
• The Molecular Counterpart of the Galactic Center Arched Filament HII Complex: OVRO Observations of the CS(2-1) Line
• Origin of the Galactic Diffuse X-ray Emission: Iron K-shell Line Diagnostics
• H3+ Spectroscopy and the Ionization Rate of Molecular Hydrogen in the Central Few Parsecs of the Galaxy
• Reaction Studies of Neutral Atomic $\mathrm{C}$ with ${\mathrm{H}}_3^{+}$ using a Merged-Beams Apparatus
• Low-luminosity X-ray sources and the Galactic ridge X-ray emission
• Widespread Rotationally-Hot Hydronium Ion in the Galactic Interstellar Medium
• Merged-beams Reaction Studies of O + H_3^+
• The Molecular Chemistry of Diffuse and Translucent Clouds in the Line-of-Sight to Sgr B2
• Ionized gas at the edge of the Central Molecular Zone
• A Hot Helium Plasma in the Galactic Center Region
• Background Infrared Sources for Studying the Galactic Center's Interstellar Gas
• Molecular Hydrogen Emission from the Inner 400 Parsecs of the Galaxy
• A Complete Survey of the Central Molecular Zone in NH3
• The Galactic plane at faint X-ray fluxes - II. Stacked X-ray spectra of a sample of serendipitous XMM-Newton sources
• Dense Molecular Clouds In The Galactic Center Region : I. HCN (J=1$-$0) DATA
• A Viscous Heating Mechanism for the Hot Plasma in the Galactic Center Region
• CH 3 GHz Observations of the Galactic Center
• Outflowing Diffuse Gas in the Active Galactic Nucleus of NGC 1068
• Properties of dust in the Galactic center region probed by AKARI far-infrared spectral mapping - detection of a dust feature
• High-spectral resolution M-band observations of CO Rot-Vib absorption lines towards the Galactic center

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• Chandra large-scale mapping of the Galactic center: Probing high-energy structures around the central molecular zone
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• AzTEC Survey of the Central Molecular Zone: Increasing Spectral Index of Dust with Density
• The population of Galactic centre filaments III: candidate radio and stellar sources
• Parsec-scale cosmic-ray ionisation rate in Orion
• Sagittarius B1 -- A Patchwork of H II Regions and PhotoDissociation Regions
• New Constraints on Cosmic Particle Populations at the Galactic Center using X-ray Observations of the Molecular Cloud Sagittarius B2
• Cosmic rays cannot explain the high ionisation rates in the Galactic centre
• How to create Sgr A East: Where did the supernova explode?
• H${}_3^{+}$ absorption and emission in local U/LIRGs with JWST/NIRSpec: Evidence for high H${}_2$ ionization rates
• Nonthermal filaments from the tidal destruction of clouds in the Galactic center
• G0.173-0.42: an X-ray and radio magnetized filament near the galactic center
• The Interstellar Medium toward the Galactic Center Source 2MASS J17470898-2829561
• Self-modulation of cosmic rays in molecular clouds: Imprints in the radio observations
• Atomic Carbon in the Central Molecular Zone of the Milky Way : Possible Cosmic-ray Induced Chemistry or Time-Dependent Chemistry Associated with SNR Sagittarius A East
• Exclusion of cosmic rays from molecular clouds by self-generated electric fields
• The JWST-NIRCam View of Sagittarius C. II. Evidence for Magnetically Dominated HII Regions in the CMZ
• Search for H${}_3^{+}$ isotopologues toward CRL 2136 IRS 1
• Feedback between Sgr A and B : AGN-Starburst Connection in the Galactic Centre
• The Central 300 pc of the Galaxy Probed by Infrared Spectra of H${}_3^{+}$ and CO: III. Locations of Sgr B2 and Star $\iota$
• Turbulent Pressure Heats Gas and Suppresses Star Formation in Galactic Bar Molecular Clouds
• Not gone with the Wind: Survival of High-Velocity Molecular Clouds in the Galactic center
• Cloud-Cloud Collision in the Galactic Center Arc
• Constraining the low-energy cosmic ray flux in the central molecular zone from MeV nuclear deexcitation line observations
• Chemical templates of the Central Molecular Zone. Shock and protostellar object signatures under Galactic Center conditions
• High Energy Emission from the Galactic Center
• Chemistry of Dark Molecular Clouds