Extended emission associated with young HII regions

Abstract

We have used the Australia Telescope Compact Array (ATCA) to make observations of a sample of eight young ultra-compact HII regions, selected on the basis that they have associated class II methanol maser emission. We have made observations sensitive to both compact and extended structures and find both to be present in most sources. The scale of the extended emission in our sample is in general less than that observed towards samples based on IRAS properties, or large single-dish flux densities. Our observations are consistent with a scenario where extended and compact radio continuum emission coexists within HII regions for a significant period of time. We suggest that these observations are consistent with a model where HII evolution takes place within hierarchically structured molecular clouds. This model is the subject of a companion paper (Shabala et al. 2005) and addresses both the association between compact and extended emission and UCHII region lifetime problem.

11 pages, 9 figures, accepted for publication in MNRAS

References in corpus (10)

• Radio Continuum and Recombination Line Study of UC HII Regions with Extended Envelopes
• The Molonglo Galactic Plane Survey: I. Overview and Images
• Clumpy Ultracompact HII Regions I: Fully Supersonic Wind-blown Models
• Multi-transition study and new detections of class II methanol masers
• Continuum emission associated with 6.7-GHz methanol masers
• High resolution observations of 6.7-GHz methanol masers with the LBA
• Detection of new sources of methanol emission at 107 and 108 GHz with the Mopra telescope
• Ground-state OH observations towards NGC 6334
• Mid-Infrared Imaging of NGC 6334 I
• High-Resolution Mid-Infrared Imaging of G339.88-1.26

Cited by in corpus (24)

• Methanol masers : Reliable tracers of the early stages of high-mass star formation
• ATLASGAL --- properties of compact HII regions and their natal clumps
• A Keplerian-like disk around the forming O-type star AFGL 4176
• The RMS Survey: Radio observations of candidate massive YSOs in the southern hemisphere
• A SCUBA imaging survey of ultracompact HII regions: The environments of massive star formation
• First Parallax Measurements Towards a 6.7 GHz Methanol Maser with the Australian Long Baseline Array - Distance to G339.884-1.259
• A search for hypercompact HII regions in the Galactic Plane
• SiO Outflow Signatures Toward Massive Young Stellar Objects with Linearly Distributed Methanol Masers
• The SOFIA Massive (SOMA) Star Formation Survey. II. High Luminosity Protostars
• A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176
• Detection of 36 GHz Class I Methanol Maser Emission Towards NGC 4945
• Ultracompact H II Regions with Extended Emission: The Complete View
• The mid-infrared environments of 6.7 GHz Methanol Masers from the Methanol Multi-Beam Survey
• Beyond the Solar Circle $-$ Trends in Massive Star Formation Between the Inner and Outer Galaxy
• The first high-resolution observations of 19.9-GHz methanol masers
• The relationship between Class I and Class II methanol masers at high angular resolution
• On the massive young stellar object AFGL4176: High-spatial-resolution multi-wavelength observations and modeling
• Evolution of HII regions in hierarchically structured molecular clouds
• Investigations of the Class I methanol masers in NGC 4945
• Detection of 84-GHz class I methanol maser emission towards NGC 253
• Ultracompact HII regions with extended emission: The case of G43.89-0.78 and its molecular environment
• A sensitive search for predicted methanol maser transitions with the Australia Telescope Compact Array
• A multi-wavelength study of Galactic H II regions with extended emission
• The Extended Emission of Ultracompact HII Regions: An Overview and New Observations