Seminars and Colloquia at ESO Garching and on the campus
Star formation takes place in the densest and coldest parts of the interstellar medium (ISM), in dark molecular clouds. These are swept up by multiple supernova explosions on scales of several hundred parsec. While condensing out of the warm ISM, the clouds are continuously fed with fresh gas. Thus, the turbulent substructure and magnetic field properties are imprinted during cloud formation. The formation of dense clouds from the multi-phase ISM, the onset of star formation, and the evolution of the molecular clouds under the impact of stellar feedback from newly born massive stars is studied in high-resolution simulations within the SILCC project. In this talk I will give an overview of the physics and chemistry involved in molecular cloud formation and evolution. After the onset of star formation, the latter is governed by stellar feedback from newly born massive stars. The detailed cloud substructure determines the clouds' vulnerability to stellar feedback processes, in particular to ionizing radiation. Moreover, the ionization state of the gas can be highly variable on scales of tens of parsec due to small-scale turbulent motions within the star-forming clouds, which shield and release the ionizing radiation. This leads to a flickering of the young HII regions on the scale of ~10 pc. On scales of several 100 pc and time scales of tens of Mega-years, the combined feedback from star clusters leads to a reduced star formation rate, such that long depletion time scales are observed.
The study of the inner gaseous disc of YSOs is crucial to understand the physical processes ruling disc evolution and its connection with planet formation. In this talk, I will present our results on the inner disc properties of the CTTS RW AurA. The RW Aur system has captured the attention of astronomers for its dimming events. By using X-SHOOTER spectra obtained when the star was in a bright and in a dim state, we compare the NIR CO emission in order to shed light on this mystery. In general, the NIR CO emission traces a warm (T=2000-5000K) and dense (NCO>1e12cm-2) gas as expected in the innermost region of discs. Both states need a cool (T=2600K) and dense (NCO=7e20cm-2) gas to reproduce the observations, with the emitting region located just inside the dust sublimation radius. By comparing the SED (from ~300 to ~1000 nm) and the CO emission of both states, we find that the dimming can be due to absorption by a layer of large grains with optical depth slowly declining from 2.8 to 1.6. The accretion rate remains constant (Macc~2e-8 Mo/yr) if one assumes that the same layer of dust also occults the accretion line emitting region. This excludes accretion bursts as the main cause of RW AurA brightness variability.
Our view of the gas and its physical conditions in the central region of AGN has been enriched by the discover of fast and massive outflows of HI and molecular gas. These outflows can be driven by radiation/winds but also by the interaction of the radio plasma with the ISM. Understanding the origin and quantifying their impact requires to trace their location and derive their physical conditions (density of the gas, mass, mass outflow rate and kinetic energy of the outflow etc.). Particularly interesting has been the finding that in the first phase of their life, jet in radio galaxies can be particularly effective in driving such outflows. This crucial phase is at the heart of the idea of feedback, therefore particularly relevant for studying feedback in action.
In this talk, I will present some of the results we have obtained to trace jet-driven HI and molecular gas outflows down to scales ranging from hundred to tens of pc. The impact of low-power radio jets will be discussed and the comparison with the predictions from numerical simulations will also be presented. Outflows of up to 100 Msun/yr have been found in molecular gas using ALMA while the HI observed with VLBI is showing that the outflowing gas is clumpy as also predicted from numerical simulations. I will describe the kinematics of the gas and its conditions and the relevance they may have for feedback.
We review the status of the Supernova/Gamma-Ray Burst connection. Several pieces of evidence suggest that long duration Gamma-ray Bursts (GRBs) are associated with type Ic Supernovae (SNe). Current estimates of SN and GRB rates show that only a tiny fraction of massive stars, likely less than 2%, are able to produce GRBs. The reasons for this small ratio will be discussed.
We compare resolved and unresolved observations of the CO and dust continuum emission from star-forming galaxies at z~2. The molecular gas phase of the interstellar medium is a crucial component of star-forming galaxies, hosting, and providing the fuel for, star formation. Constraining the total mass and spatial distribution of molecular gas is therefore critical to understanding the evolutionary state of a galaxy, which can be characterised by how efficiently, and where, star formation is occurring. To determine the total molecular gas mass of high-z galaxies, the community currently relies on two main approaches: measuring either (1) a CO line luminosity, or, (2) dust continuum emission. These molecular gas tracers have been observed for large samples of high-z galaxies with ALMA, and it is assumed that the two lead to equivalent measurements of the molecular gas content. But, recent low-resolution imaging indicates that the CO and dust continuum may trace different galactic regions, with the dust continuum emission being more centrally concentrated. In this talk I will present our comparisons of the CO and dust-derived molecular gas properties of Main Sequence galaxies at z~2 and will discuss the implications for future molecular gas studies with ALMA.