Alberto Garcia de la Fuente

Physical structure of the envelopes of intermediate-mass protostars

Context. Intermediate mass protostars provide a bridge between low- and high-mass protostars. Furthermore, they are an important component of the UV interstellar radiation field. Despite their relevance, little is known about their formation process. Aims. We present a systematic study of the physical structure of five intermediate mass, candidate Class 0 protostars. Our two goals are to shed light on the first phase of intermediate mass star formation and to compare these protostars with low- and high-mass sources. Methods. We derived the dust and gas temperature and density profiles of the sample. We analysed all existing continuum data on each source and modelled the resulting SED with the 1D radiative transfer code DUSTY. The gas temperature was then predicted by means of a modified version of the code CHT96. Results. We found that the density profiles of five out of six studied intermediate mass envelopes are consistent with the predictions of the “inside-out” collapse theory. We compared several physical parameters, like the power law index of the density profile, the size, the mass, the average density, the density at 1000 AU and the density at 10 K of the envelopes of low-, intermediate, and high-mass protostars. When considering these various physical parameters, the transition between the three groups appears smooth, suggesting that the formation processes and triggers do not substantially differ.

Fueling the central engine of radio galaxies. I. The molecular/dusty disk of 4C 31.04

We report the detection of a massive (Mgas > 5 × 10 9 M� ) molecular/dusty disk of 1.4 kpc-size fueling the central engine of the compact symmetric object (CSO) 4C 31.04, based on high-resolution (0.5 �� –1.2 �� ) observations done with the IRAM Plateau de Bure interferometer (PdBI). These observations allow us for the first time to detect and map the continuum emission from dust at 218 GHz in the disk of a CSO. The case for a massive disk is confirmed by detection of strong HCO + (1–0) line emission and absorption. The molecular gas mass of 4C 31.04 is in the range 0.5 × 10 10 −5 × 10 10 M� . While the distribution and kinematics of the gas roughly correspond to those of a rotating disk, we find evidence of distortions and non-circular motions that suggest the disk is not in a dynamically relaxed state. We discuss the implications of these results for the understanding of the evolution of radio galaxies.