On Turbulent Pressure Confinement of Ultra-Compact HII Regions
نویسندگان
چکیده
It has been proposed recently that the small size and long lifetime of ultracompact (UC) HII regions could be due to pressure confinement if the thermal pressure of the ambient gas is higher than previous estimates. We point out that confinement by thermal pressure alone implies emission measures in excess of observed values. We show that turbulent pressure, inferred from observed non-thermal velocities, is sufficient to confine UC HII regions and explain their longevity. We predict an anti-correlation between the size of UC HII regions and the velocity dispersion of the ambient neutral gas, and show that it is consistent with existing observations. Subject headings: ISM: HII regions—ISM: kinematics and dynamics—stars: formation—turbulence
منابع مشابه
High-excitation CS and C34S towards ultracompact HII regions
We have used the JCMT telescope to observe the J=5–4 and J=7–6 rotational transitions of CS and C34S towards 19 ultracompact Hii regions. The main goal was to extend the survey of Cesaroni et al. (1991) to a larger sample of sources and to higher energy transitions sensitive to the densest, hottest molecular gas. In all cases we find gas with nH2 ' 105– 106 cm−3 associated with the ultracompact...
متن کاملExtended emission associated with young Hii regions
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 genera...
متن کاملVLBI observations of 6 GHz OH masers in three ultra-compact H ii regions
Following our successful analysis of VLBI observations of the 2Π 3 2 , J = 2 , F = 3− 3 and F = 2− 2 excited OH emission at 6035 and 6031 MHz in W3(OH), we have analyzed the same transitions in three other ultra-compact HII regions, M17, ON1, and W51. The restoring beams were in the range 6 to 30 milliarc sec. The F = 3−3 and 2−2 hyperfine transitions of OH were both mapped in ON1. Seven 6035 M...
متن کاملRelative Evolutionary Time Scale of Hot Molecular Cores with Respect to Ultra Compact HII Regions
Using the Owens Valley and Nobeyama Radio Observatory interferometers, we carried out an unbiased search for hot molecular cores and ultracompact (UC) HII regions toward the high-mass star forming region G19.61–0.23. In addition, we performed 1.2 mm imaging with SIMBA, and retrieved 3.5 and 2 cm images from the VLA archive data base. The newly obtained 3 mm image brings information on a cluster...
متن کاملAustralia Telescope Compact Array Survey of Candidate Ultra-Compact and Buried HII Regions in the Magellanic Clouds
We present a systematic survey for ultracompact H II (UCH II ) regions in the Magellanic Clouds. Understanding the physics of massive star formation (MSF) is a critical astrophysical problem. The study of MSF began in our galaxy with surveys of UCH II regions, but before now this has not been done for other galaxies. We selected candidates based on their Infrared Astronomical Satellite (IRAS) c...
متن کامل