Core to ultracompact HII region evolution in the W49A massive protocluster

Abstract

We aim to identify and characterize cores in the high-mass proto-cluster W49, determine their evolutionary stages and measure the associated lifetimes. We built a catalog of 129 cores extracted from an ALMA 1.3 mm continuum image at 0.26" (2900 au) angular resolution. The association between cores and Hyper/Ultra Compact HII (H/UC HII) regions was established from the analysis of VLA 3.3 cm continuum and H30$\alpha$ line observations. We also looked for emission of hot molecular cores (HMCs) using the methyl formate doublet at 218.29 GHz. We identified 40 cores associated with an H/UC HII region and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC HII region and/or a HMC are assumed to be high-mass protostellar cores, while the rest of the core population likely consists in prestellar cores and low-mass protostellar cores. We found a good agreement between the two tracers of ionized gas, with 23 common detections and only four cores detected at 3.3 cm and not in H30$\alpha$. The spectral indexes from 3.3 cm to 1.3 mm range from 1, for the youngest cores with partially optically thick free-free emission, to about -0.1, that is optically thin free-free emission obtained for cores likely more evolved. Using as a reference the H/UC HII regions, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about $6\times 10^4$ yr and $1.4\times 10^5$ yr, respectively. We also showed that HMC can co-exist with H/UC HII regions during a short fraction of the core lifetime, about $2\times 10^4$ yr. This indicates a rapid dispersal of the inner molecule envelope once the HC HII is formed.

15 pages, 7 figures. Accepted for publication in A&A

References in corpus (39)

• CASA, the Common Astronomy Software Applications for Radio Astronomy
• High-Mass Star and Massive Cluster Formation in the Milky Way
• Global Hierarchical Collapse In Molecular Clouds. Towards a Comprehensive Scenario
• H II regions: Witnesses to massive star formation
• The Simultaneous Formation of Massive Stars and Stellar Clusters
• The formation of massive stars: accretion, disks and the development of hypercompact HII regions
• Parallaxes for W49N and G048.60+0.02: Distant Star Forming Regions in the Perseus Spiral Arm
• Understanding Spatial and Spectral Morphologies of Ultracompact H II Regions
• The Luminosity Functions and Timescales of MYSOs and Compact HII regions
• The Early Evolution of Massive Stars: Radio Recombination Line Spectra
• Exploring molecular complexity with ALMA (EMoCA): Detection of three new hot cores in Sagittarius B2(N)
• Outflow-Confined H II Regions. I. First Signposts of Massive Star Formation
• Formation of an O-Star Cluster by Hierarchical Accretion in G20.08-0.14 N
• Hot Corinos Chemical Diversity: Myth or Reality?
• Multiscale, multiwavelength extraction of sources and filaments using separation of the structural components: getsf
• MUSCLE W49 : A Multi-Scale Continuum and Line Exploration of the Most Luminous Star Formation Region in the Milky Way. I. Data and The Mass Structure of the Giant Molecular Cloud
• Toward gas exhaustion in the W51 high-mass protoclusters
• ATOMS:ALMA Three-millimeter Observations of Massive Star-forming regions -- III :Catalogues of candidate hot molecular cores and Hyper/Ultra compact HII regions
• Cloud Structure of Galactic OB Cluster Forming Regions from Combining Ground and Space Based Bolometric Observations
• LEGO II: A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way Disc
• ALMA-IMF. V. Prestellar and protostellar core populations in the W43 cloud complex
• Massive Star Formation in the W49 Giant Molecular Cloud: Implications for the Formation of Massive Star Clusters
• Morphologies of Ultracompact HII Regions in W49A and Sgr B2: Prevalence of Shells and a Modified Classification Scheme
• ALMA-IMF II -- investigating the origin of stellar masses: Continuum Images and Data Processing
• Water Masers in W49 North and Sagittarius B2
• Investigating fragmentation of gas structures in OB cluster-forming molecular clump G33.92+0.11 with 1000 AU resolution observations of ALMA
• W49A: A starburst triggered by expanding shells
• Molecular analysis of a high-mass prestellar core candidate in W43-MM1
• Feedback in W49A diagnosed with radio recombination lines and models
• Young Stellar Objects in the Massive Star Forming Region W49
• ALMA-IMF XI: The sample of hot core candidates A rich population of young high-mass proto-stars unveiled by the emission of methyl formate
• ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -XIV. Properties of resolved UC Hii regions
• Relative Evolutionary Time Scale of Hot Molecular Cores with Respect to Ultra Compact HII Regions
• ALMA-IMF IV -- A comparative study of the main hot cores in W43-MM1: detection, temperature and molecular composition
• Massive Protostars in a Protocluster -- A Multi-Scale ALMA View of G35.20-0.74N
• Recombination Lines and Molecular Gas from Hypercompact HII regions in W51 A
• Time-Variable Radio Recombination Line Emission in W49A
• Flux Density Variations at 3.6 cm in the Massive Star-Forming Region W49A
• Star burst in W49N presumably induced by cloud-cloud collision

Cited by in corpus (3)

• Reexploring Molecular Complexity with ALMA: Insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2)
• ALMA-IMF XVII -- Census and lifetime of high-mass prestellar cores in 14 massive protoclusters
• The interdependence between density PDF, CMF and IMF and their relation with Mach number in simulations