Temperature and kinematics of protoclusters with intermediate and high-mass stars: the case of IRAS 05345+3157
1 INAF – Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, 50125 Firenze, Italy
2 School of Physics and Astrophysics, University of Leeds, Leeds, LS2 9JT, UK
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS78, Cambridge, MA 02138, USA
4 INAF – Istituto di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy
5 INAF-Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliare 100, 00133 Roma, Italy
6 Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB-Facultat de Ciències, Torre C5-parell 2, 08193 Bellaterra, Spain
Received: 26 September 2011
Accepted: 13 March 2012
Context. Improving our understanding of the complex star formation process in clusters requires studies of star-forming clouds to search for dependencies of the physical properties on environmental variables, such as overall density, stellar crowding and feedback from massive (proto-)stars.
Aims. We aim to map at small spatial scales the temperature and the velocity field in the protocluster associated with IRAS 05345+3157, which contains both intermediate-/high-mass protostellar candidates and starless condensations, and is thus an excellent location to investigate the role of massive protostars on protocluster evolution.
Methods. We observed the ammonia (1, 1) and (2, 2) inversion transitions with the VLA. Ammonia is the best thermometer for dense and cold gas, and the observed transitions have critical densities able to trace the kinematics of the intracluster gaseous medium.
Results. The ammonia emission is extended and distributed in two filamentary structures. The starless condensations are colder than the star-forming cores, but the gas temperature across the whole protocluster is higher (by a factor of 1.3−1.5) than that measured typically in both infrared dark clouds and low-mass protoclusters. The non-thermal contribution to the observed line broadening is at least a factor of 2 larger than the expected thermal broadening even in starless condensations, contrary to the close-to-thermal line widths measured in low-mass quiescent dense cores. The NH3/N2H+ abundance ratio is greatly enhanced (a factor of 10) in the pre-stellar core candidates, probably due to freeze-out of most molecular species heavier than He.
Conclusions. The more massive and evolved objects likely play a dominant role in the physical properties and kinematics of the protocluster. The high level of turbulence and the fact that the measured core masses are larger than the expected thermal Jeans masses indicate that turbulence likely was an important factor in the initial fragmentation of the parental clump and can provide support against further fragmentation of the cores.
Key words: stars: formation / radio lines: ISM / ISM: individual objects: IRAS 05345+3157 / ISM: kinematics and dynamics / ISM: molecules
© ESO, 2012