The geometry of the gas surrounding the Central Molecular Zone: on the origin of localised molecular clouds with extreme velocity dispersions

Abstract

Observations of molecular gas near the Galactic centre ($|l|<10^{\circ }$, $|b|<1^{\circ }$) reveal the presence of a distinct population of enigmatic compact clouds which are characterised by extreme velocity dispersions ($\Delta v>100km/s$). These Extended Velocity Features (EVFs) are very prominent in the datacubes and dominate the kinematics of molecular gas just outside the Central Molecular Zone (CMZ). The prototypical example of such a cloud is Bania Clump 2. We show that similar features are naturally produced in simulations of gas flow in a realistic barred potential. We analyse the structure of the features obtained in the simulations and use this to interpret the observations. We find that the features arise from collisions between material that has been infalling rapidly along the dust lanes of the Milky Way bar and material that belongs to one of the following two categories: (i) material that has `overshot' after falling down the dust lanes on the opposite side; (ii) material which is part of the CMZ. Both types of collisions involve gas with large differences in the line-of-sight velocities, which is what produces the observed extreme velocity dispersions. Examples of both categories can be identified in the observations. If our interpretation is correct, we are directly witnessing (a) collisions of clouds with relative speeds of $\sim 200km/s$ and (b) the process of accretion of fresh gas onto the CMZ.

12 pages, 10 figures. Movies of the simulation are available at the link provided in the Supplementary Information section

References in corpus (41)

• The Structure of Cold Dark Matter Halos
• E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
• The CO-to-H2 Conversion Factor
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• The mass distribution and gravitational potential of the Milky Way
• The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• A 100-parsec elliptical and twisted ring of cold and dense molecular clouds revealed by Herschel around the Galactic Center
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline
• Global properties of the HI distribution in the outer Milky Way
• Molecular gas kinematics within the central 250 pc of the Milky Way
• Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines
• Modelling CO formation in the turbulent interstellar medium
• TreeCol: a novel approach to estimating column densities in astrophysical simulations
• Gas flow in barred potentials
• Gas flow in barred potentials - III. Effects of varying the Quadrupole
• Mass inflow rate into the Central Molecular Zone: observational determination and evidence of episodic accretion
• A theoretical explanation for the Central Molecular Zone asymmetry
• Approximations for modelling CO chemistry in GMCs: a comparison of approaches
• On the temperature structure of the Galactic Centre cloud G0.253+0.016
• Nuclear Spirals in the inner Milky Way
• Signature of an Intermediate-Mass Black Hole in the Central Molecular Zone of Our Galaxy
• A dynamical mechanism for the origin of nuclear rings
• The ATCA HI Galactic Center Survey
• On the Interpretation of the l-v Features in the Milky Way Galaxy
• Millimetre-wave Emission from an Intermediate-Mass Black Hole Candidate in the Milky Way
• Transverse kinematics of the Galactic bar-bulge from VVV and Gaia
• Indication of Another Intermediate-mass Black Hole in the Galactic Center
• H2O Southern Galactic Plane Survey (HOPS): Paper III - Properties of Dense Molecular Gas across the Inner Milky Way
• Formation of Galactic Center Magnetic Loops
• The large scale dust lanes of the Galactic bar
• A Detailed Observational Study of Molecular Loops 1 and 2 in the Galactic Center
• SPH Simulations of Galactic Gaseous Disk with Bar: Distribution and Kinematic Structure of Molecular Clouds toward the Galactic Center
• Stochastic Noncircular Motion and Outflows Driven by Magnetic Activity in the Galactic Bulge Region
• Multiplicity of nuclear dust lanes and dust lane shocks in the Milky Way bar
• Discovery of Molecular Loop 3 in the Galactic Center: Evidence for a Positive-Velocity Magnetically Floated Loop towards $L=355^{\circ }-359^{\circ }$
• La Freccia Rossa: An IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate
• The foot points of the Giant Molecular Loops in the Galactic center region
• Magnetic Activity in the Galactic Centre Region -- Fast Downflows along Rising Magnetic Loops

Cited by in corpus (33)

• Giant Molecular Cloud Catalogues for PHANGS-ALMA: Methods and Initial Results
• Molecular Gas Properties on Cloud Scales Across the Local Star-forming Galaxy Population
• Dynamical Equilibrium in the Molecular ISM in 28 Nearby Star-Forming Galaxies
• Simulations of the Milky Way's central molecular zone -- I. Gas dynamics
• Simulations of the Milky Way's central molecular zone -- II. Star formation
• The Life Cycle of the Central Molecular Zone. I: Inflow, Star Formation, and Winds
• Gas Dynamics in the Galaxy: Total Mass Distribution and the Bar Pattern Speed
• Jeans modelling of the Milky Way's nuclear stellar disc
• Dynamically Driven Inflow onto the Galactic Center and its Effect upon Molecular Clouds
• CHIMPS2: Survey description and ${}^{12}$CO emission in the Galactic Centre
• ALMA Observations of Massive Clouds in the Central Molecular Zone: Ubiquitous Protostellar Outflows
• The Life Cycle of the Central Molecular Zone. II: Distribution of atomic and molecular gas tracers
• Three-Dimensional Structure of the Central Molecular Zone
• WISDOM Project -- XV. Giant Molecular Clouds in the Central Region of the Barred Spiral Galaxy NGC 5806
• WISDOM Project XII. Clump properties and turbulence regulated by clump-clump collisions in the dwarf galaxy NGC404
• ALMA uncovers highly filamentary structure towards the Sgr E region
• SPLASH: The Southern Parkes Large-Area Survey in Hydroxyl -- Data Description & Release
• Evidence of a Cloud-Cloud Collision from Overshooting Gas in the Galactic Center
• Unusual Galactic HII Regions at the Intersection of the Central Molecular Zone and the Far Dust Lane
• Towards the impact of GMC collisions on the star formation rate
• Revealing Gas Inflows towards the Galactic Central Molecular Zone
• Living on the edge of the Central Molecular Zone: G1.3 is the more likely candidate for gas accretion into the CMZ
• Star Formation in Extreme Environments: A 200 pc High Velocity Gas Stream in the Galactic Centre
• Molecular Fraction in the Galactic Center: The Central Molecular and HI Zones
• Nitrogen Abundance Distribution in the inner Milky Way
• A Multiwavelength Study of the Sgr B Region: Contiguous Cloud-Cloud Collisions Triggering Widespread Star Formation Events?
• The dynamical impact of cosmic rays in the Rhea magnetohydrodynamics simulations
• Turbulent Pressure Heats Gas and Suppresses Star Formation in Galactic Bar Molecular Clouds
• Gas Transfer Between the Inner 3-kpc Disk and the Galactic Central Molecular Zone
• Discovery of a giant molecular loop in the central region of NGC 253
• Chemical Evolution in Nuclear Stellar Discs
• Parabolic-like Trend in SiO Ratios throughout the Central Molecular Zone: Possible Signature of a Past Nuclear Activity in the Galactic Center
• Insights into the structure and kinematics of a Milky Way-like galaxy