The role of low-mass star clusters in the formation of massive stars

Víctor Manuel Rivilla Rodríguez

Departamento de Astrofísica

Año 2014

Massive stars (M>8M⊙) are the main source of energy and turbulence injection into the interstellar medium (ISM) of galaxies. Despite their importance, their formation process is still not well understood, being one of the most debated topic in modern Astrophysics.

Several theories have been proposed to explain the formation of the most massive stars: i) monolithic gravitational collapse and core accretion; ii) coalescence of low- mass stars in dense stellar clusters; and iii) competitive accretion of material by low- and intermediate-mass stars in the cluster potential well.

While the classic theory of monolithic core accretion requires low levels of frag- mentation of the parental gas condensation, coalescence and competitive accretion models require high levels of fragmentation resulting in a dense population of low- mass stars. Therefore, to distinguish between the different scenarios, it is crucial to establish how the parental condensation fragments by studying the distribution of low-mass stars in massive star cradles.

According to the scenario in which massive stars are born escorted by a dense population of low-mass stars, the turbulence injected by molecular outflows driven by young stars may affect the collapse and fragmentation processes as well as the accretion rates onto the potential well. Therefore, the outflow-driven feedback may play an important role in the formation of the cluster and the massive stars.

This thesis is focused on the role of stellar clusters of pre-main sequence (PMS) low-mass stars in the mechanisms leading to the formation of massive stars. We study the young low-mass stellar population in three nearby massive star-forming regions: Orion, DR21 and Monoceros R2. The characterization of this population is a challenge because it is usually still deeply embedded in the parental molecular cloud. Large amounts of dust and gas produce high extinctions that prevent their detection in the optical and even in the near-infrared (IR) wavelengths. Only X-ray, radio/(sub)millimeter and very deep IR observations are able to penetrate into the massive star cradles and reveal the low-mass stellar population. Thus, we use the X-ray catalogs provided by the space telescope Chandra, complementing them with deep IR surveys. We study the properties of the low-mass stellar population (such as the spatial distribution, the clustering, the stellar densities, the extinction distribution or the evolutionary phase) and discuss which massive star formation scenario better agrees with our results.

Additionally, with the aim of better understanding both the properties of the members of these young clusters and the molecular environment of massive star cradles, we carry out new Very Large Array (VLA) radio continuum multi-epoch observations of Orion, and new Submillimeter Array (SMA) observations of the central region of Monoceros R2.

To assess the impact of outflow feedback, we study the role of the outflow-driven turbulence in two clusters of outflows embedded in massive star-forming regions, such as the Orion OMC1-S region and the central region of Monoceros R2. […]

Datos de interés

Supervisores: Jesús Martín-Pintado Martín (CAB, Ángeles Isabel Díaz Beltrán
Universidad: UAM. Departamento de Física Teórica; Centro de Astrobiología (CAB)
Fecha de lectura: 24/07/2014