Distributed star formation throughout the Galactic Center cloud Sgr B2

Abstract

We report ALMA observations with resolution $\approx 0.5$" at 3 mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000 AU. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact HII regions and young stellar objects (YSOs). Most of the newly-detected sources are YSOs with gas envelopes which, based on their luminosities, must contain objects with stellar masses $M_{\ast }\gtrsim 8$ M${}_{\odot }$. Their spatial distribution spread over a $\sim 12\times 3$ pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated `starburst' within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density ($N(H_2)\gtrsim 2\times 10^{23}$ cm${}^{-2}$), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear ${\Sigma }_{\ast }-{\Sigma }_{gas}$ relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds.

arXiv commentAccepted to ApJ. Full resolution at http://keflavich.github.io/SgrB2_ALMA_3mm_Mosaic/sgrb2_cores_compressed.pdf, source code repository at https://github.com/keflavich/SgrB2_ALMA_3mm_Mosaic/, and data at DOI 10.11570/17.0007. 33 pages, 23 figures

References in corpus (91)

• Astropy: A Community Python Package for Astronomy
• On the variation of the Initial Mass Function
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• The SIMBAD astronomical database
• The Spitzer c2d Legacy Results: Star Formation Rates and Efficiencies; Evolution and Lifetimes
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• A General Theory of Turbulence-Regulated Star Formation, From Spirals to ULIRGs
• The Formation of Massive Stars from Turbulent Cores
• Clouds, filaments and protostars: the Herschel Hi-GAL Milky Way
• The Star Formation Rate of Turbulent Magnetized Clouds: Comparing Theory, Simulations, and Observations
• On the Star Formation Rates in Molecular Clouds
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• A multi-scale multi-frequency deconvolution algorithm for synthesis imaging in radio interferometry
• The Star Formation Rate and Gas Surface Density Relation in the Milky Way: Implications for Extragalactic Studies
• The Star Formation Rate of Supersonic MHD Turbulence
• On the fraction of star formation occurring in bound stellar clusters
• The SCUBA Legacy Catalogue: Continuum Objects Detected by SCUBA
• A 100-parsec elliptical and twisted ring of cold and dense molecular clouds revealed by Herschel around the Galactic Center
• Variations in the Galactic star formation rate and density thresholds for star formation
• A Minimum Column Density of 1 g cm^-2 for Massive Star Formation
• SCUBA-2: iterative map-making with the Sub-Millimetre User Reduction Facility
• What controls star formation in the central 500 pc of the Galaxy?
• An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
• Analytical star formation rate from gravoturbulent fragmentation
• The 6-GHz methanol multibeam maser catalogue I: Galactic Centre region, longitudes 345 to 6
• Hi-GAL, the Herschel infrared Galactic Plane Survey: photometric maps and compact source catalogues. First data release for Inner Milky Way: +68°> l > -70°
• Hierarchical Star Formation from the Time-Space Distribution of Star Clusters in the Large Magellanic Cloud
• The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline
• A Trigonometric Parallax of Sgr B2
• Dense gas in the Galactic central molecular zone is warm and heated by turbulence
• Molecular gas kinematics within the central 250 pc of the Milky Way
• The Herschel Orion Protostar Survey: Spectral Energy Distributions and Fits Using a Grid of Protostellar Models
• A Correlation Between Surface Densities of Young Stellar Objects and Gas in Eight Nearby Molecular Clouds
• Star Formation in the Central 400 pc of the Milky Way: Evidence for a Population of Massive YSOs
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• A deep submillimetre survey of the Galactic Centre
• A Catalog of X-ray Point Sources from Two Megaseconds of Chandra Observations of the Galactic Center
• Star formation rates and efficiencies in the Galactic Centre
• Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines
• Characterizing Precursors to Stellar Clusters with Herschel
• A $\lambda$20cm Survey of the Galactic Center Region I: Detection of Numerous Linear Filaments
• The physical and chemical structure of Sagittarius B2, I. Three-dimensional thermal dust and free-free continuum modeling on 100 au to 45 pc scales
• The Bolocam Galactic Plane Survey IX: Data Release 2 and Outer Galaxy Extension
• Candidate super star cluster progenitor gas clouds possibly triggered by close passage to Sgr A*
• Comparing molecular gas across cosmic time-scales: the Milky Way as both a typical spiral galaxy and a high-redshift galaxy analogue
• Flux calibration of the Herschel-SPIRE photometer
• The Galactic Center Molecular Cloud Survey. I. A Steep Linewidth-Size Relation & Suppression of Star Formation
• The linewidth-size relationship in the dense ISM of the Central Molecular Zone
• Understanding Spatial and Spectral Morphologies of Ultracompact H II Regions
• The Bolocam Galactic Plane Survey IV: 1.1 and 0.35 mm Dust Continuum Emission in the Galactic Center Region
• A cluster in the making: ALMA reveals the initial conditions for high-mass cluster formation
• A modular set of synthetic spectral energy distributions for young stellar objects
• The Galactic Center Cloud G0.253+0.016: A Massive Dense Cloud with low Star Formation Potential
• The Massive Star-forming Regions Omnibus X-ray Catalog
• The physical and chemical structure of Sagittarius B2. II. Continuum millimeter emission of SgrB2(M) and SgrB2(N) with ALMA
• The Dust Emissivity Spectral Index in the Starless Core TMC-1C
• G0.253+0.016: A centrally condensed, high-mass protocluster
• STATCONT: A statistical continuum level determination method for line-rich sources
• Stellar Kinematics of Young Clusters in Turbulent Hydrodynamic Simulations
• 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
• Nuclear Spirals in the inner Milky Way
• Galactic structure based on the ATLASGAL 870mum survey
• Abundant Methanol Masers but no New Evidence for Star Formation in GCM0.253+0.016
• The Galactic Center Molecular Cloud Survey. II. A Lack of Dense Gas & Cloud Evolution along Galactic Center Orbits
• G11.92-0.61-MM2: A Bonafide Massive Prestellar Core?
• Comparing Young Massive Clusters and their Progenitor Clouds in the Milky Way
• The observable prestellar phase of the IMF
• Early stage massive star formation near the Galactic Center: Sgr C
• The Molecular Gas Environment in the 20 km s${}^{-1}$ Cloud in the Central Molecular Zone
• The reliability of observational measurements of column density probability distribution functions
• Dust Emissivity in the Star-Forming Filament OMC 2/3
• HP2 survey: III The California Molecular Cloud--A Sleeping Giant Revisited
• Comparison of absolute gain photometric calibration between Planck/HFI and Herschel/SPIRE at 545 and 857 GHz
• High-mass star-forming cloud G0.38+0.04 in the Galactic Center Dust Ridge contains H2CO and SiO masers
• 90GHz and 150GHz observations of the Orion M42 region. A sub-millimeter to radio analysis
• Temperature structures in Galactic Center clouds - Direct evidence for gas heating via turbulence
• Water Masers in W49 North and Sagittarius B2
• Evidence of Short Timescale Flux Density Variations of UC HII regions in Sgr B2 Main and North
• Star formation with disc accretion and rotation I. Stars between 2 and 22 Msol at solar metallicity
• Fourier Plane Image Combination by Feathering
• MUSTANG 3.3 Millimeter Continuum Observations of Class 0 Protostars
• Shocked and Scorched: The Tail of a Tadpole in an Interstellar Pond
• Environment and Protostellar Evolution
• Sgr B2(N): A bipolar outflow and rotating hot core revealed by ALMA
• Are Large, Cometary-Shaped Proplyds really (free-floating) EGGs?
• The 200-pc Molecular Cylinder in the Galactic Centre
• The Ionized Circumstellar Envelopes of Orion Source I and the Becklin Neugebauer Object

Cited by in corpus (69)

• Astrochemistry During the Formation of Stars
• Re-exploring Molecular Complexity with ALMA (ReMoCA): Interstellar detection of urea
• Complex organic molecules in the Galactic Centre: the N-bearing family
• The 1.28 GHz MeerKAT Galactic Center Mosaic
• Cloud-cloud collisions and triggered star formation
• Forming Super Star Clusters in the Central Starburst of NGC 253
• 'The Brick' is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016
• The complex chemistry of hot cores in Sagittarius B2(N): Influence of cosmic-ray ionization and thermal history
• 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
• Propargylimine in the laboratory and in space: millimetre-wave spectroscopy and first detection in the ISM
• The Role of Outflows, Radiation Pressure, and Magnetic Fields in Massive Star Formation
• CMZoom: Survey Overview and First Data Release
• Prevalent externally-driven protoplanetary disc dispersal as a function of the galactic environment
• Star Formation Rates of Massive Molecular Clouds in the Central Molecular Zone
• The Physical and chemical structure of Sagittarius B2 -- IV. Converging filaments in the high-mass cluster forming region Sgr B2(N)
• ALMA Observations of Massive Clouds in the Central Molecular Zone: Jeans Fragmentation and Cluster Formation
• The MPIfR-MeerKAT Galactic Plane survey I -- System setup and early results
• A Census of Early Phase High-Mass Star Formation in the Central Molecular Zone
• Cloud-cloud collisions in the common foot point of molecular loops 1 and 2 in the Galactic Center
• Super Star Clusters in the Central Starburst of NGC 4945
• Massive Star Formation via the Collapse of Subvirial and Virialized Turbulent Massive Cores
• CHIMPS2: Survey description and ${}^{12}$CO emission in the Galactic Centre
• Young massive star cluster formation in the Galactic Centre is driven by global gravitational collapse of high-mass molecular clouds
• Star formation in 'the Brick': ALMA reveals an active proto-cluster in the Galactic centre cloud G0.253+0.016
• A high cluster formation efficiency in the Sagittarius B2 complex
• ALMA-IMF II -- investigating the origin of stellar masses: Continuum Images and Data Processing
• The physical and chemical structure of Sagittarius B2 -- V. Non-thermal emission in the envelope of Sgr B2
• On the abiotic origin of dimethyl sulfide: discovery of DMS in the Interstellar Medium
• A Massive Star is Born: How Feedback from Stellar Winds, Radiation Pressure, and Collimated Outflows Limits Accretion onto Massive Stars
• Sulphur and carbon isotopes towards Galactic centre clouds
• ALMA observations of RCW 120 Fragmentation at 0.01pc scale
• CMZoom II: Catalog of Compact Submillimeter Dust Continuum Sources in the Milky Way's Central Molecular Zone
• Entropy Driven Winds: Outflows and Fountains Lifted Gently by Buoyancy
• SOFIA/HAWC+ Far-InfraRed Polarimetric Large Area CMZ Exploration (FIREPLACE) Survey I: General Results from the Pilot Program
• Structure and kinematics of shocked gas in Sgr B2: further evidence of a cloud-cloud collision from SiO emission maps
• Constraining the population of isolated massive stars within the Central Molecular Zone
• Deuterium fractionation as a multi-phase component tracer in the Galactic Centre
• Submillimeter imaging of the Galactic Center starburst Sgr B2. Warm molecular, atomic, and ionized gas far from massive star-forming cores
• The physical and chemical structure of Sagittarius B2 -- VI. UCHII regions in Sgr B2
• SOFIA/FORCAST Galactic Center Legacy Survey: Overview
• A global view on star formation: The GLOSTAR Galactic plane survey IV. Radio continuum detections of young stellar objects in the Galactic Centre region
• The "Red Radio Ring": Ionised and Molecular Gas in a Starburst/Active Galactic Nucleus at $z\sim 2.55$
• AzTEC Survey of the Central Molecular Zone: Data Reduction, Analysis, and Preliminary Results
• Discovery of 14NH3 (2,2) maser emission in Sgr B2-Main
• A wind-blown bubble in the Central Molecular Zone cloud G0.253+0.016
• 3-D CMZ IV: Distinguishing Near vs. Far Distances in the Galactic Center Using Spitzer and Herschel
• Virial Clumps in Central Molecular Zone Clouds
• Fiery Cores: Bursty and Smooth Star Formation Distributions across Galaxy Centers in Cosmological Zoom-in Simulations
• APEX-SEPIA660 Early Science: Gas at densities above $10^7$ cm${}^{-3}$ towards OMC-1
• Expanding the submillimeter wave spectroscopy and astronomical search for thioacetamide (CH3CSNH2) in the ISM
• Benchmarking the IRDC G351.77-0.53: Gaia DR3 distance, mass distribution, and star formation content
• Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence
• The initial conditions for young massive cluster formation in the Galactic Centre: convergence of large-scale gas flows
• SOFIA-upGREAT imaging spectroscopy of the [C II] 158um fine structure line of the Sgr B region in the Galactic center
• CMZoom III: Spectral Line Data Release
• Molecular isotopologue measurements toward super star clusters and the relation to their ages in NGC253 with ALCHEMI
• A Multiwavelength Study of the Sgr B Region: Contiguous Cloud-Cloud Collisions Triggering Widespread Star Formation Events?
• Dual-band Unified Exploration of Three CMZ Clouds (DUET). Cloud-wide census of continuum sources showing low spectral indices
• G337.342-0.119 (the "Pebble"): A Cold, Dense, High-Mass Molecular Cloud with Unusually Large Linewidths and a Candidate High-Mass Star Cluster Progenitor
• The complex multi-scale structure in simulated and observed emission maps of the proto-cluster cloud G0.253+0.016 (`the Brick')
• Discovery of non-metastable ammonia masers in Sagittarius B2
• Shock waves in Interstellar Cloud-Cloud and Wind-Cloud Collisions
• Molecular clumps disguising their star formation efficiency per freefall time: What we can do not to be fooled
• Unusual Infrared Emission toward Sgr B2: Possible Planar C${}_{24}$
• Linear filament and nested cluster evolution tomography (LANCET) I. Capture the evolution of dense gas in 14-parsec filament G316.8
• Backlighting young stellar objects in the Central Molecular Zone: an ensemble-averaged abundance structure of methanol ices
• Clustered Star Formation in the center of NGC 253 Contributes to Driving the Ionized Nuclear Wind
• Mass Segregation in the CMZoom Survey