Collapse scenarios in magnetized star-forming regions

Abstract

Turbulence, magnetic fields and gravity driven flows are important for the formation of new stars. Although magnetic fields have been proven to be important in the formation of stars, only a few works have been done combining magnetic field and kinematic information. Such studies are important to analyze both gravity and gas dynamics and be able to compare them with the magnetic field. In this thesis we will combine dust polarization studies with kinematic analysis towards different star-forming regions. We aim to study the physical properties at core scales (<0.1 pc) from molecular line and dust emission, and study the role of the magnetic field in their dynamic evolution. For this, we will use millimeter and submillimeter observational data taken towards low- and high- mass star-forming regions in different environments and evolutionary states.

The first project is the study of the physical, chemical and magnetic properties of the pre-stellar core FeSt1-457 in the Pipe nebula. We studied the emission of the molecular line N2H+(1-0) which is a good tracer of dense gas and therefore describes well the structure of the core. In addition, we detected more than 15 molecular lines and found a clear chemical spatial differentiation for molecules with nitrogen, oxygen and sulfur. Using the ARTIST radiative transfer code (Brinch & Hogerheijde 2010, Padovani et al., 2011, 2012, Jørgensen et al., 2014), we simulated the emission of the different molecules detected and estimated their abundance. In addition, we estimated the magnetic field properties of the core (using the Chandrasekhar-Fermi approximation) from polarization data previously obtained by Alves et al., (2014). Finally, we found interesting correlations between the polarization properties and the chemistry in the region.

The second project is the study of a high-mass star-forming region called NGC6334V. NGC6334V is in a more advanced evolutionary state and in an environment surrounded by other massive star-forming regions. During the project we studied the magnetic field from the polarized emission of the dust and also the kinematics of the gas from the molecular line emission of the different tracers of dense gas. From the molecular emission of the gas tracing the envelope of the dense core, we see two different velocity structures separated by 2 km/s and converging towards the potential well in the region. In addition, the magnetic field also presents a bimodal pattern following the distribution of the two velocity structures. Finally, we compared the observational results with 3D magnetohydrodynamic simulations of star-forming regions dominated by gravity.

The last project is the study of a lower-mass star-forming region, L1287. From the data obtained with the SMA, the dust continuum structure shows six main dense cores with masses between ~0.4 and 4 solar masses. The dense gas tracer DCN(3-2) shows two velocity structures separated by 2-3 km/s, converging towards the highest-density region, the young stellar object IRAS00338+6312, in a similar scenario to the one observed in the higher-mass case of NGC6334V.

Finally, the studies of the pre-stellar core FeSt1-457 and the massive region NGC6334V, show how the magnetic field has been overcome by gravity and is not enough to avoid the gravitational collapse. In addition, NGC6334V and the lower- mass region L1287 present very similar scenarios with the material converging from large scales (~0.1 pc) to the potential wells of both regions at smaller scales (~0.02 pc) through two dense gas flows separated by 2-3 km/s. In a similar scenario, FeSt1-457 is located just in the region where two dense gas structures separated by 3 km/s appear to converge.

La turbulencia, el campo magnético y la gravedad juegan un papel importante en la formación estelar. Aunque se ha mostrado que el campo magnético es importante, sólo se han llevado a cabo un número limitado de trabajos combinando el estudio del campo magnético y la cinemática del gas. Este tipo de trabajos son esenciales para estudiar la gravedad y la dinámica del gas y poder compararlas con el campo magnético a las mismas escalas espaciales. En este trabajo combinamos estudios de polarización a partir de la emisión del polvo, con el análisis de la cinemática del gas en diferentes regiones de formación estelar. El objetivo es estudiar las propiedades físicas a escalas de núcleos densos (<0.1 pc) a partir de la emisión molecular y del polvo, y estudiar el papel del campo magnético en la evolución dinámica de las regiones. Para ello hemos utilizado datos observacionales milimétricos y submilimétricos.

Los estudios se han realizado en 3 regiones de formación estelar. El núcleo pre- estelar FeSt 1-457 localizado en un entorno aislado y muy magnetizado en la nebulosa de la Pipa. NGC 6334 V, una región de mayor masa, en un estado evolutivo más avanzado y en un entorno rodeado de otras regiones de formación estelar masiva. Y L1287, una región menos masiva pero con características similares a NGC 6334 V, con presencia de gas de alta velocidad y fuentes centimétricas e infrarrojas.

Los estudios del núcleo pre-estelar FeSt 1-457 y la región de formación estelar de alta masa NGC 6334 V, muestran como el campo magnético ha sido superado por la gravedad y no es suficiente para evitar el colapso gravitatorio. Además NGC 6334 V y la región de menor masa L1287 presentan escenarios muy similares, con el material convergiendo desde escalas grandes hacia los pozos de potencial de ambas regiones a escalas más pequeñas a través de flujos de gas denso separados por 2-3 km/s. En un escenario parecido, FeSt 1-457 se encuentra justo en la zona donde parecen converger dos flujos de gas denso separados por 3 km/s.