The Survey of Water and Ammonia in the Galactic Center (SWAG): Molecular Cloud Evolution in the Central Molecular Zone

Abstract

The Survey of Water and Ammonia in the Galactic Center (SWAG) covers the Central Molecular Zone (CMZ) of the Milky Way at frequencies between 21.2 and 25.4 GHz obtained at the Australia Telescope Compact Array at $\sim 0.9$ pc spatial and $\sim 2.0$ km s${}^{-1}$ spectral resolution. In this paper, we present data on the inner $\sim 250$ pc ($1.4^{\circ }$) between Sgr C and Sgr B2. We focus on the hyperfine structure of the metastable ammonia inversion lines (J,K) = (1,1) - (6,6) to derive column density, kinematics, opacity and kinetic gas temperature. In the CMZ molecular clouds, we find typical line widths of $8-16$ km s${}^{-1}$ and extended regions of optically thick ($\tau >1$) emission. Two components in kinetic temperature are detected at $25-50$ K and $60-100$ K, both being significantly hotter than dust temperatures throughout the CMZ. We discuss the physical state of the CMZ gas as traced by ammonia in the context of the orbital model by Kruijssen et al. (2015) that interprets the observed distribution as a stream of molecular clouds following an open eccentric orbit. This allows us to statistically investigate the time dependencies of gas temperature, column density and line width. We find heating rates between $\sim 50$ and $\sim 100$ K Myr${}^{-1}$ along the stream orbit. No strong signs of time dependence are found for column density or line width. These quantities are likely dominated by cloud-to-cloud variations. Our results qualitatively match the predictions of the current model of tidal triggering of cloud collapse, orbital kinematics and the observation of an evolutionary sequence of increasing star formation activity with orbital phase.

68 pages, 44 figures, accepted for publication in ApJS; slightly compressed images due to file size limitations, high resolution available at http://www2.mpia-hd.mpg.de/homes/krieger/data/Krieger_SWAG.pdf

References in corpus (20)

• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• Magnetic Fields in High-Mass Infrared Dark Clouds
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• Gas flow models in the Milky Way embedded bars
• The Bolocam Galactic Plane Survey IV: 1.1 and 0.35 mm Dust Continuum Emission in the Galactic Center Region
• Turbulence sets the initial conditions for star formation in high-pressure environments
• G0.253+0.016: A centrally condensed, high-mass protocluster
• Cosmic-Ray Heating of Molecular Gas in the Nuclear Disk: Low Star Formation Efficiency
• Seeding the Galactic Centre gas stream: gravitational instabilities set the initial conditions for the formation of protocluster clouds
• Tracing the Conversion of Gas into Stars in Young Massive Cluster Progenitors
• The dynamics and star-forming potential of the massive Galactic centre cloud G0.253+0.016
• A multi-wavelength view of the Galactic center dust ridge reveals little star formation
• Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, Water and Methanol Masers in the Nuclear Starburst of NGC 253
• Temperature structures in Galactic Center clouds - Direct evidence for gas heating via turbulence
• The orbital motion of the Quintuplet cluster - a common origin for the Arches and Quintuplet clusters?
• High Resolution Observations of Molecular Lines in Arp 220: Kinematics, Morphology, and Limits on the Applicability of the Ammonia Thermometer

Cited by in corpus (56)

• Photodissociation and X-Ray Dominated Regions
• The 1.28 GHz MeerKAT Galactic Center Mosaic
• Impact of low-energy cosmic rays on star formation
• Low-J CO Line Ratios From Single Dish CO Mapping Surveys and PHANGS-ALMA
• Simulations of the Milky Way's central molecular zone -- I. Gas dynamics
• 'The Brick' is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016
• Prebiotic precursors of the primordial RNA world in space: Detection of NH${}_2$OH
• Simulations of the Milky Way's central molecular zone -- II. Star formation
• The dynamical evolution of molecular clouds near the Galactic Centre - II. Spatial structure and kinematics of simulated clouds
• Cloud-cloud collision as drivers of the chemical complexity in Galactic Centre molecular clouds
• High-energy particles and radiation in star-forming regions
• 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
• Ubiquitous velocity fluctuations throughout the molecular interstellar medium
• Which feedback mechanisms dominate in the high-pressure environment of the Central Molecular Zone?
• CMZoom: Survey Overview and First Data Release
• Star Formation Rates of Massive Molecular Clouds in the Central Molecular Zone
• Molecular Gas Properties and CO-to-H2 Conversion Factors in the Central Kiloparsec of NGC 3351
• Isomers in Interstellar Environments (I): The Case of Z- and E-Cyanomethanimine
• Star formation in 'the Brick': ALMA reveals an active proto-cluster in the Galactic centre cloud G0.253+0.016
• The dynamical evolution of molecular clouds near the Galactic Centre -- III. Tidally--induced star formation in protocluster clouds
• ALMA Observations of Massive Clouds in the Central Molecular Zone: Ubiquitous Protostellar Outflows
• The Galactic Center as a laboratory for theories of gravity and dark matter
• The centres of M83 and the Milky Way: opposite extremes of a common star formation cycle
• A 2-3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946
• SOFIA/HAWC+ Far-InfraRed Polarimetric Large Area CMZ Exploration (FIREPLACE) Survey I: General Results from the Pilot Program
• The Life Cycle of the Central Molecular Zone. II: Distribution of atomic and molecular gas tracers
• Deuterium fractionation as a multi-phase component tracer in the Galactic Centre
• The turbulent gas structure in the centers of NGC253 and the Milky Way
• A 6.7 GHz methanol maser survey of the central molecular zone
• Measuring the Orbits of the Arches and Quintuplet Clusters using HST and Gaia: Exploring Scenarios for Star Formation Near the Galactic Center
• Evidence of a Cloud-Cloud Collision from Overshooting Gas in the Galactic Center
• A wind-blown bubble in the Central Molecular Zone cloud G0.253+0.016
• Virial Clumps in Central Molecular Zone Clouds
• Unusual Galactic HII Regions at the Intersection of the Central Molecular Zone and the Far Dust Lane
• AzTEC Survey of the Central Molecular Zone: Increasing Spectral Index of Dust with Density
• Galactic center gamma-ray production by cosmic rays from stellar winds and Sgr A East
• Processing of hydroxylamine, NH2OH, an important prebiotic precursor, on interstellar ices
• JWST reveals widespread CO ice and gas absorption in the Galactic Center cloud G0.253+0.016
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde V. The massive filament DR21
• Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence
• Observations of multiple NH${}_3$ transitions in W33
• The initial conditions for young massive cluster formation in the Galactic Centre: convergence of large-scale gas flows
• Star Formation in Extreme Environments: A 200 pc High Velocity Gas Stream in the Galactic Centre
• H2CN/H2NC abundance ratio: a new potential temperature tracer for the interstellar medium
• CMZoom III: Spectral Line Data Release
• Evidence for an interaction between the Galactic Center clouds M0.10-0.08 and M0.11-0.11
• Modelling of ionising feedback with Smoothed Particle Hydrodynamics and Monte Carlo Radiative Transfer on a Voronoi grid
• 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
• 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
• The magnetic field in the Flame nebula
• The complex multi-scale structure in simulated and observed emission maps of the proto-cluster cloud G0.253+0.016 (`the Brick')
• ALMA observations of massive clouds in the central molecular zone: slim filaments tracing parsec-scale shocks
• Chemical templates of the Central Molecular Zone. Shock and protostellar object signatures under Galactic Center conditions
• KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping in Ammonia lines (KAGONMA): Star formation feedback on dense molecular gas in the W33 complex
• 3D CMZ V: A new orbital model of our Galaxy's Center, informed by data across the electromagnetic spectrum
• Chemistry of Dark Molecular Clouds