How is Cold Gas Loaded into Galactic Nuclear Outflows?

Abstract

The origin of the multiphase gas within the Fermi/eROSITA bubbles is crucial for understanding Galactic Center (GC) feedback. We use HI4PI data to investigate the kinematics and physical properties of high-velocity clouds (HVCs) toward the GC. Our results reveal that the HVCs exhibit a distinct asymmetric distribution, closely associated with the bar-driven tilted dust lanes and the distorted overshooting streams. We propose that powerful nuclear outflows interact with these gas-rich, off-plane structures, striping and entraining cold gas from the outer Galactic regions (R_GC~0.5--1.7 kpc) rather than solely from the region of the central molecular zone (CMZ; R_GC<0.3 kpc). In this scenario, as the Galactic bar drives gas inflows along the dust lanes, nuclear outflows simultaneously break through the CMZ, sweeping up and ablating cold gas from the boundary layer of these pre-existing structures. This process naturally accounts for the observed high turbulence, complex spectral signatures, and anomalous spatial-kinematic gas patterns, as well as multiwavelength asymmetries of the bubbles. The HVCs are accelerated to about 230--340 km/s over a dynamical time of ~3--6 Myr. When the multiphase, inhomogeneous composition of the gas is included, the estimated gas outflow rate reaches ~1 Msun/yr. This value is comparable to the bar-driven inflow rate, indicating a tightly coupled gas cycle in the inner Galaxy. Our research highlights the critical role of bar-driven gas dynamics and nuclear feedback in the secular evolution of the Milky Way, offering a valuable paradigm for investigating gas cycles in external galaxies.

Published in ApJ; Typo corrections and reference additions

References in corpus (56)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Trigonometric Parallaxes Of High-Mass Star Forming Regions: Our View Of The Milky Way
• Cool Outflows in Galaxies and their Implications
• The Large-scale Bipolar Wind in the Galactic Center
• The growth and entrainment of cold gas in a hot wind
• Detection of large-scale X-ray bubbles in the Milky Way halo
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• The Launching of Cold Clouds by Galaxy Outflows I: Hydrodynamic Interactions with Radiative Cooling
• The cold interstellar medium of galaxies in the Local Universe
• The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg
• The Impact of Star Formation Feedback on the Circumgalactic Medium
• Gas flow models in the Milky Way embedded bars
• Multiphase Gas and the Fractal Nature of Radiative Turbulent Mixing Layers
• How cold gas continuously entrains mass and momentum from a hot wind
• Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event
• The Galactic Centre Chimney
• Interaction of a cold cloud with a hot wind: the regimes of cloud growth and destruction and the impact of magnetic fields
• A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center's Giant Outflows
• Probing the Fermi Bubbles in Ultraviolet Absorption: A Spectroscopic Signature of the Milky Way's Biconical Nuclear Outflow
• A Dynamical Model for Gas Flows, Star Formation, and Nuclear Winds in Galactic Centres
• Survival and mass growth of cold gas in a turbulent, multiphase medium
• Radiative Mixing Layers: Insights from Turbulent Combustion
• Mass inflow rate into the Central Molecular Zone: observational determination and evidence of episodic accretion
• Nuclear Outflow of the Milky Way: Studying the Kinematics and Spatial Extent of the Northern Fermi Bubble
• A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey
• The Interaction of the Fermi Bubbles with the Milky Way's Hot Gas Halo
• Blowing in the Milky Way wind: neutral hydrogen clouds tracing the Galactic nuclear outflow
• Atomic Hydrogen in a Galactic Center Outflow
• Multi-wavelength features of Fermi Bubbles as signatures of a Galactic wind
• The large-scale ionization cones in the Galaxy
• Cold gas in the Milky Way's nuclear wind
• The Galactic center chimneys: The base of the multiphase outflow of the Milky Way
• Shock-multicloud interactions in galactic outflows -- II. Radiative fractal clouds and cold gas thermodynamics
• Milky Way Disk-Halo Transition in HI: Properties of the Cloud Population
• The large scale dust lanes of the Galactic bar
• Observation of Acceleration of HI Clouds Within the Fermi Bubbles
• Mapping Outflowing Gas in the Fermi Bubbles: a UV Absorption Survey of the Galactic Nuclear Wind
• Tracing the Milky Way Nuclear Wind with 21cm Atomic Hydrogen Emission
• Clues to the origin of Fermi Bubbles from OVIII/OVII line ratio
• Thermal and chemical properties of the eROSITA bubbles from Suzaku observations
• Molecular gas distribution perpendicular to the Galactic plane
• Molecular Gas within the Milky Way's Nuclear Wind
• Direct observations of the atomic-molecular phase transition in the Milky Way's nuclear wind
• The high-velocity cloud complex Galactic Center Negative as seen by EBHIS and GASS. I. Cloud catalog and global properties
• Discovery of High-Velocity H$\alpha$ Emission in the Direction of the Fermi Bubble
• A CO Funnel in the Galactic Centre: Molecular Counterpart of the Northern Galactic Chimney?
• Caught in the Act: A Metal-Rich High-Velocity Cloud in the Inner Galaxy
• Revealing Gas Inflows towards the Galactic Central Molecular Zone
• CO Emission Delineating the Interface between the Milky Way Nuclear Wind Cavity and the Gaseous Disk
• Morphological Evidence for the eROSITA Bubbles Being Giant and Distant Structures
• Discovery of diffuse optical emission lines from the inner Galaxy: Evidence for LI(N)ER-like gas
• Cold molecular gas in the hot nuclear wind of the Milky Way
• Gas Dynamics in the Central Molecular Zone and its connection with the Galactic Bar
• Gas Transfer Between the Inner 3-kpc Disk and the Galactic Central Molecular Zone
• A New High-latitude H I Cloud Complex Entrained in the Northern Fermi Bubble