|Dynamics of the ultracompact HII region Monoceros R2: solving the lifetime paradox of young massive star forming region
|Ultracompact (UC) HII regions represent one of the earliest phases in massive star formation. They are characterized by extreme UV irradiation (G0&amp;gt;10^5 Habings), small physical scales (&amp;lt;0.1 pc) and are embedded in dense molecular clouds. HII regions are expected to expand at velocities of the order of the sound speed (10km-s) and remain ultracompact for about 3000 years. Therefore, only a few dozen should exist in the Galaxy. However, many more UCHIIs have been observed, corresponding to lifetimes one to two orders of magnitude larger. A number of models have been proposed to solve this problem, but all have shortcomings. Our ability to test these models depends on good informations about the morphology and the kinematics of the sources. Mon R2 is the closest ultracompact HII region (d=830 pc), the only one that can be resolved by Herschel and undoubtedly a case study. Full modeling of the CO lines previously observed with HIFI suggests that the high velocity gas arises from the layer of warm (&amp;gt;100 K) and dense (&amp;gt;5x10^6 cm-3) gas confining the UCHII region. The line profiles are well reproduced assuming that this layer is expanding at the relatively high velocity of 1.5km-s, corresponding to a lifetime of about 10^5 years. Our kinematical study of the region is however limited by the scarce HIFI observations that hinder a full 3D modeling. We propose to observe with HIFI fully sampled maps of several atomic and molecular species (CII, CO, 13CO, CH, CH+) and single pointed observations of OH+ to trace the kinematics of the different phases of MonR2. The understanding of the dynamics and energetics of UCHII regions is key to study the feedback process of newly formed massive stars in their native molecular cloud, and therefore the evolution of giant molecular clouds. In extragalactic research, these energetic environments could dominate the physical and ...chemical conditions in evolved starbursts like M82 and in the most distant galaxies.
|Kinematics of the ionized-to-neutral interfaces in Monoceros R2 . Pilleri P. et al. . Astronomy & Astrophysics, Volume 561, id.A69, 6 pp. . 561 . 10.1051/0004-6361/201322638 . 2014A&A...561A..69P ,
|HIFI_HifiPoint_dbs, HIFI_HifiMapping_load-raster, HIFI_HifiMapping_fly
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT2_ppilleri_1, SPG v14.1.0. https://doi.org/10.5270/esa-iis2qyc