From forced collapse to H ii region expansion in Mon R2: Envelope density structure and age determination with Herschel

P., Didelon (1) , F., Motte (1) , Pascal Tremblin (2, 1, 3) , T., Hill (1, 4) , S., Hony (1) , M. Hennemann (1) , P., Hennebelle (1, 5) , L. D., Anderson (6) , F., Galliano (1) , N., Schneider (7, 1) , T., Rayner (8) , K., Rygl (9) , François Louvet (1) , Annie Zavagno (10) , V., Konyves (1) , M., Sauvage (1) , Ph., Andre (1) , Sylvain Bontemps (11) , N., Peretto (1, 8) , M., Griffin (8) , M., Gonzalez (1) , V., Lebouteiller (1) , D., Arzoumanian (1) , J.-P., Bernard (12) , M., Benedettini (13) , J., Di Francesco (14) , A., Menshchikov (1) , Vincent Minier , Q., Nguyen Luong (1) , P., Palmeirim (1, 5) , A., Rivera-Ingraham (15) , S., Pezzuto (13) , D., Russeil (10) , D., Ward-Thompson (16, 7) , G. J., White (17)

1 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
2 University of Exeter
3 MDLS - Maison de la Simulation
4 Joint ALMA Office
5 DAP - Département d'Astrophysique (ex SAP)
6 NRAO - National Radio Astronomy Observatory
7 OASU - Observatoire aquitain des sciences de l'univers
8 School of Physics and Astronomy [Cardiff]
9 ESTEC - European Space Research and Technology Centre
10 LAM - Laboratoire d'Astrophysique de Marseille
11 FORMATION STELLAIRE 2015
12 CESR - Centre d'étude spatiale des rayonnements
13 IAPS - Istituto di Astrofisica e Planetologia Spaziali - INAF
14 NRC - National Research Council of Canada
15 IRAP - Institut de recherche en astrophysique et planétologie
16 Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy [Preston]
17 RAL - STFC Rutherford Appleton Laboratory

The surroundings of HII regions can have a profound influence on their development, morphology, and evolution. This paper explores the effect of the environment on H II regions in the MonR2 molecular cloud. We aim to investigate the density structure of envelopes surrounding HII regions and to determine their collapse and ionisation expansion ages. The Mon R2 molecular cloud is an ideal target since it hosts an H II region association. Column density and temperature images derived from Herschel data were used together to model the structure of HII bubbles and their surrounding envelopes. The resulting observational constraints were used to follow the development of the Mon R2 ionised regions with analytical calculations and numerical simulations. The four hot bubbles associated with H II regions are surrounded by dense, cold, and neutral gas envelopes. The radial density profiles are reminiscent of those of low-mass protostellar envelopes. The inner parts of envelopes of all four HII regions could be free-falling because they display shallow density profiles. As for their outer parts, the two compact HII regions show a density profile, which is typical of the equilibrium structure of an isothermal sphere. In contrast, the central UCHii region shows a steeper outer profile, that could be interpreted as material being forced to collapse. The size of the heated bubbles, the spectral type of the irradiating stars, and the mean initial neutral gas density are used to estimate the ionisation expansion time, texp, 0.1Myr,for the dense UCHII and compact HII regions and 0.35 Myr for the extended HII region. The envelope transition radii between the shallow and steeper density profiles are used to estimate the time elapsed since the formation of the first proto stellar embryo, Tinf : 1Myr, for the ultra-compact, 1.5 / 3Myr for the compact, and greater than 6Myr for the extended HII regions.

Mots clés: Astrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics

Domaines: Astrophysique galactique [astro-ph.GA]

P., Didelon, F., Motte, Pascal Tremblin, T., Hill, S., Hony, et al.. From forced collapse to H ii region expansion in Mon R2: Envelope density structure and age determination with Herschel. Astronomy and Astrophysics - A&A, 2015, 584, pp.id.A4. ⟨10.1051/0004-6361/201526239⟩. ⟨hal-01225735⟩