Cosmic-Ray Heating of Molecular Gas in the Nuclear Disk: Low Star Formation Efficiency

Abstract

Understanding the processes occurring in the nuclear disk of our Galaxy is interesting in its own right, as part of the Milky Way Galaxy, but also because it is the closest galactic nucleus. It has been more than two decades since it was recognized that the general phenomenon of higher gas temperature in the inner few hundred parsecs by comparison with local clouds in the disk of the Galaxy. This is one of the least understood characteristics of giant molecular clouds having a much higher gas temperature than dust temperature in the inner few degrees of the Galactic center. We propose that an enhanced flux of cosmic-ray electrons, as evidenced recently by a number of studies, are responsible for directly heating the gas clouds in the nuclear disk, elevating the temperature of molecular gas ($\sim$ 75K) above the dust temperature ($\sim$ 20K). In addition we report the detection of nonthermal radio emission from Sgr B2-F based on low-frequency GMRT and VLA observations. The higher ionization fraction and thermal energy due to the impact of nonthermal electrons in star forming sites have important implications in slowing down star formation in the nuclear disk of our galaxy and nuclei of galaxies.

12 pages, one figure, ApJL (in press)

References in corpus (5)

• Slow Star Formation in Dense Gas: Evidence and Implications
• The Origin of Diffuse X-ray and $\gamma$-ray Emission from the Galactic Center Region: Cosmic Ray Particles
• APEX mapping of H3O+ in the Sgr B2 region
• Enhanced Cosmic Ray Flux and Ionization for Star Formation in Molecular Clouds Interacting with Supernova Remnants
• Non-Thermal Continuum toward SGRB2(N-LMH)

Cited by in corpus (20)

• Wild at Heart:-The Particle Astrophysics of the Galactic Centre
• The Survey of Water and Ammonia in the Galactic Center (SWAG): Molecular Cloud Evolution in the Central Molecular Zone
• GBT Multiwavelength Survey of the Galactic Center Region
• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• Statistical Properties of the Population of the Galactic Center Filaments: The Spectral Index and Equipartition Magnetic Field
• The large scale dust lanes of the Galactic bar
• Molecular chemistry and the missing mass problem in PNe
• The Mid-Infrared Colors of the ISM and Extended Sources at the Galactic Center
• Dynamics of the Parker-Jeans instability of gaseous disks including the effect of cosmic rays
• A Large--Scale Spectroscopic Survey of Methanol and OH Line Emission from the Galactic Center: Observations and Data
• Evidence of a Cloud-Cloud Collision from Overshooting Gas in the Galactic Center
• Australia Telescope Compact Array Radio Continuum 1384 and 2368 Mhz Observations of Sagittarius B
• A low-luminosity type-1 QSO sample: IV. Molecular gas contents and conditions of star formation in three nearby Seyfert galaxies
• HCN $J$=4-3, HNC $J$=1-0, ${\mathrm{H}}^{13}\mathrm{CN}$ $J$=1-0, and $\mathrm{H}{\mathrm{C}}_3\mathrm{N}$ $J$=10-9 Maps of Galactic Center Region II.: Physical Properties of Dense Gas Clumps and Probability of Star Formation
• Self-modulation of cosmic rays in molecular clouds: Imprints in the radio observations
• Turbulent Pressure Heats Gas and Suppresses Star Formation in Galactic Bar Molecular Clouds
• Probing magnetic fields with Square Kilometre array and its precursors
• When did the initial mass function become bottom-heavy?
• Influence of the back-reaction of streaming cosmic rays on magnetic field generation and thermal instability
• Physical conditions in Centaurus A's northern filaments II: Does the HCO${}^{+}$ emission highlight the presence of shocks?