A Detailed Observational Study of Molecular Loops 1 and 2 in the Galactic Center

Abstract

Fukui et al. (2006) discovered two huge molecular loops in the Galactic center located in (l, b) ~ (355 deg-359 deg, 0 deg-2 deg) in a large velocity range of -180-40 km s^-1. Following the discovery, we present detailed observational properties of the two loops based on NANTEN 12CO(J=1-0) and 13CO(J=1-0) datasets at 10 pc resolution including a complete set of velocity channel distributions and comparisons with HI and dust emissions as well as with the other broad molecular features. We find new features on smaller scales in the loops including helical distributions in the loop tops and vertical spurs. The loops have counterparts of the HI gas indicating that the loops include atomic gas. The IRAS far infrared emission is also associated with the loops and was used to derive an X-factor of 0.7(+/-0.1){\times}10^20 cm^-2 (K km s^-1)^-1 to convert the 12CO intensity into the total molecular hydrogen column density. From the 12CO, 13CO, H I and dust datasets we estimated the total mass of loops 1 and 2 to be ~1.4 {\times} 106 Msun and ~1.9 {\times} 10^6 Msun, respectively, where the H I mass corresponds to ~10-20% of the total mass and the total kinetic energy of the two loops to be ~10^52 ergs. An analysis of the kinematics of the loops yields that the loops are rotating at ~47 km s-1 and expanding at ~141 km s^-1 at a radius of 670 pc from the center. Fukui et al. (2006) presented a model that the loops are created by the magnetic flotation due to the Parker instability with an estimated magnetic field strength of ~150 μG. We present comparisons with the recent numerical simulations of the magnetized nuclear disk by Machida et al. (2009) and Takahashi et al. (2009) and show that the theoretical results are in good agreements with the observations. The helical distributions also suggest that some magnetic instability plays a role similarly to the solar helical features.

arXiv comment40 pages, 22 figures, submitted to publication in PASJ

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Cited by in corpus (22)

• Non-Thermal Insights on Mass and Energy Flows Through the Galactic Centre and into the Fermi Bubbles
• The geometry of the gas surrounding the Central Molecular Zone: on the origin of localised molecular clouds with extreme velocity dispersions
• A survey of the Galactic center region in HCO+, H13CO+ and SiO
• Cloud-cloud collisions in the common foot point of molecular loops 1 and 2 in the Galactic Center
• Tracing gas accretion in the Galactic center using isotopic ratios
• Evidence for a neutral iron line generated by MeV protons from supernova remnants interacting with molecular clouds
• FOREST Unbiased Galactic Plane Imaging Survey with the Nobeyama 45-m Telescope (FUGIN) V: Dense gas mass fraction of molecular gas in the Galactic plane
• Stochastic Noncircular Motion and Outflows Driven by Magnetic Activity in the Galactic Bulge Region
• Ionized gas at the edge of the Central Molecular Zone
• Discovery of possible molecular counterparts to the infrared Double Helix Nebula in the Galactic center
• Kinetic temperatures toward X1/X2 orbit interceptions regions and Giant Molecular Loops in the Galactic center region
• Processing of polycyclic aromatic hydrocarbons in molecular-loop regions near the Galactic center revealed by AKARI
• High Excitation Molecular Gas in the Galactic Center Loops; 12CO(J =2-1 and J =3-2) Observations
• High Velocity Compact Clouds in the Sagittarius C Region
• Molecular and Atomic Gas toward HESS J1745-303 in the Galactic Center: Further Support for the Hadronic Scenario
• The foot points of the Giant Molecular Loops in the Galactic center region
• Detailed molecular observations toward the Double Helix Nebula
• Magnetic Activity in the Galactic Centre Region -- Fast Downflows along Rising Magnetic Loops
• Formation of Galactic Prominence in Galactic Central Region
• Discovery of a giant molecular loop in the central region of NGC 253
• Vertical flows and structures excited by magnetic activity in the Galactic center region
• Investigating Magnetic Activity in the Galactic Centre by Global MHD Simulation