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

Abstract

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.

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References in corpus (20)

• Formation of a Keplerian disk in the infalling envelope around L1527 IRS: transformation from infalling motions to Kepler motions
• The Electron Temperature Gradient in the Galactic Disk
• The identification of filaments on far infrared and submillimiter images. Morphology, physical conditions and relation with star formation of filamentary structure
• Understanding Spatial and Spectral Morphologies of Ultracompact H II Regions
• The Luminosity Functions and Timescales of MYSOs and Compact HII regions
• The dynamics of collapsing cores and star formation
• The Earliest Phases of Star formation observed with Herschel (EPoS): The dust temperature and density distributions of B68
• Constraining the Envelope Structure of L1527 IRS: Infrared Scattered Light Modeling
• Modelling the sulphur chemistry evolution in Orion KL
• Age, size, and position of H ii regions in the Galaxy. Expansion of ionized gas in turbulent molecular clouds
• Mopra CO Observations of the Bubble HII Region RCW120
• The Importance of the Magnetic Field from an SMA-CSO-Combined Sample of Star-Forming Regions
• Constraining the structure of the transition disk HD 135344B (SAO 206462) by simultaneous modeling of multiwavelength gas and dust observations
• Protostar Formation in Supersonic Flows: Growth and Collapse of Spherical Cores
• Colliding Filaments and a Massive Dense Core in the Cygnus OB 7 Molecular Cloud
• Deuteration around the ultracompact HII region Mon R2
• The infrared dust bubble N22: an expanding HII region and the star formation around it
• [Ne II] Observations of Gas Motions in Compact and Ultracompact H II Regions
• Spectral energy distribution modelling of Southern candidate massive protostars using the Bayesian inference method
• Tightening the belt: Constraining the mass and evolution in SDC335

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• Probing the kinematics and chemistry of the hot core Mon R 2 IRS 3 using ALMA observations
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