Searching for compact radio sources associated to UCHII regions

Abstract

Ultra-Compact (UC)HII regions represent a very early stage of massive star formation whose structure and evolution are not yet fully understood. Interferometric observations in recent years show that some UCHII regions have associated compact sources of uncertain nature. Based on this, we carried out VLA 1.3 cm observations in the A configuration of selected UCHII regions in order to report additional cases of compact sources embedded in UCHII regions. From the observations, we find 13 compact sources associated to 9 UCHII regions. Although we cannot establish an unambiguous nature for the newly detected sources, we assess some of their observational properties. According to the results, we can distinguish between two types of compact sources. One type corresponds to sources that probably are deeply embedded in the dense ionized gas of the UCHII region. These sources are being photo-evaporated by the exciting star of the region and will last for 10${}^4-10^5$ yr. They may play a crucial role in the evolution of the UCHII region as the photo-evaporated material could replenish the expanding plasma and might provide a solution to the so-called lifetime problem for these regions. The second type of compact sources is not associated with the densest ionized gas of the region. A few of these sources appear resolved and may be photo-evaporating objects such as those of the first type but with significantly lower mass depletion rates. The rest of sources of this second type appear unresolved and their properties are varied. We speculate on the similarity between the sources of the second type and those of the Orion population of radio sources.

arXiv comment33 pages, 6 figures, 4 tables. Accepted for publication in ApJ

References in corpus (27)

• Infrared Dark Clouds: precursors to star clusters
• A Parallax-based Distance Estimator for Spiral Arm Sources
• Millimetre continuum observations of southern massive star formation regions. I. SIMBA observations of cold cores
• Trigonometric Parallaxes of Massive Star Forming Regions: IV. G35.20-0.74 and G35.20-1.74
• Compact Radio Sources in Orion: New Detections, Time Variability, and Objects in OMC-1S
• Formation of an O-Star Cluster by Hierarchical Accretion in G20.08-0.14 N
• Time Variation in G24.78+0.08 A1: Evidence for an Accreting Hypercompact H II Region?
• Resolving the Circumstellar Disk Around the Massive Protostar Driving the HH 80-81 Jet
• Time Variation in the Radio Flux Density from the Bipolar Ultracompact H II Region NGC 7538 IRS1
• The infrared Hourglass cluster in M8
• The Population of Compact Radio Sources in the Orion Nebula Cluster
• Expansion of W 3(OH)
• The Gould's Belt Very Large Array Survey III. The Orion region
• Simulating protostellar evolution and radiative feedback in the cluster environment
• Evidence of Short Timescale Flux Density Variations of UC HII regions in Sgr B2 Main and North
• Multi-Epoch VLBA Observations of the Compact Wind-Collision Region in the Quadruple System Cyg OB2 #5
• High-Resolution Infrared Imaging of Herschel 36 SE: A Showcase for the Influence of Massive Stars in Cluster Environments
• Multitransitional observations of the CS core of L673
• The 2.35 year itch of Cyg OB2 #9. II. Radio monitoring
• A rotating molecular disk toward IRAS 18162-2048, the exciting source of HH 80-81
• Searching for new hypercompact HII regions
• VLBA determination of the distance to nearby star-forming regions VII. Monoceros R2
• A Multi-wavelength Study of the Massive Star-forming Region S87
• HII region variability and pre-main-sequence evolution
• The compact, time-variable radio source projected inside W3(OH): Evidence for a Photoevaporated Disk?
• Very Large Array and Jansky Very Large Array observations of the compact radio sources in M8
• A multiwavelength study of the ultracompact HII region associated with IRAS 20178+4046

Cited by in corpus (5)

• GLOSTAR -- Radio Source Catalog I: $28^{\circ }<\text{l}<36^{\circ }$ and $|b|<1^{\circ }$
• A Galactic survey of radio jets from massive protostars
• Surveys of Clumps, Cores, and Condensations in the Cygnus X: II. Radio Properties of the Massive Dense Cores
• The richness of compact radio sources in NGC 6334D to F
• The ultracompact regions G40.54+2.59 and G34.13+0.47: A new detection of compact radio sources