Ultracompact HII regions with extended emission: The complete view
Journal article, 2020

© 2019 The Author(s). In this paper, we present the results of a morphological study performed on a sample of 28 ultracompact HII (UC HII) regions located near extended free-free emission, using radio continuum (RC) observations at 3.6 cm with the C and D Very Large Array (VLA) configurations, with the aim of determining a direct connection between them. By using previously published observations in B and D VLA configurations, we compiled a final catalogue of 21 UC HII regions directly connected with the surrounding extended emission (EE). The observed morphology of most of the UC HII regions in RC emission is irregular (single- or multipeaked sources) and resembles a classical bubble structure in the Galactic plane with well-defined cometary arcs. RC images superimposed on colour composite Spitzer images reinforce the assignations of direct connection by the spatial coincidence between the UC components and regions of saturated 24 μm emission. We also find that the presence of EE may be crucial to understand the observed infrared excess because an underestimation of ionizing Lyman photons was considered in previous works (e.g. Wood & Churchwell; Kurtz, Churchwell & Wood).

ISM: bubbles

Stars: pre-main-sequence

HII regions

Radio continuum: ISM


Eduardo De La Fuente

University of Guadalajara

Alicia Porras

National Institute of Astrophysics, Optics and Electronics

Miguel A. Trinidad

Universidad de Guanajuato

S. Kurtz

Universidad Nacional Autonoma de Mexico

Simon N. Kemp

University of Guadalajara

Daniel Tafoya

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Onsala Space Observatory, Observation Support

Jose Franco

Universidad Nacional Autonoma de Mexico

Carlos Rodriguez-Rico

Universidad de Guanajuato

Monthly Notices of the Royal Astronomical Society

0035-8711 (ISSN) 1365-2966 (eISSN)

Vol. 492 1 895-914

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics



More information

Latest update

3/4/2020 3