Star formation - Making complex things understandable

Special Colloquium
Prof. Guang-Xing Li
South-Western Institute for Astronomical Research, Yunnan University, China

Star formation is among the most complex processes studied by astronomers to date. It is characterised by a multi-scale interplay between gravity, turbulence, magnetic field, galactic shear as well as ionising radiation. Because of its complexity, the physical mechanisms that drive the star formation remain unclear. I will present a few recent advancements. First, I present results from our recent study in the Galactic Center region, where, because of its unique location, shear can drastically reduce the star formation efficiency. I will present our study on the fragmentation of the Cygnus X region, where we demonstrate how the introduction of novel methods can help us to pin down the dominant process at work. Finally, I argue that in spite of years of reach, there are still plenty of undiscovered mechanisms which would drive star formation, and will present one as an example.

From Jy to mJy: a different view of local radio galaxies

Main Colloquium
Dr. Eleonora Torresi
INAF-OAS, Bologna, Italy

Radio galaxies are among the most energetic manifestation of the AGN phenomenon: indeed, they are extraordinarily relevant in addressing important unknowns relating accretion onto supermassive black holes (SMBH), the production of relativistic jets and the role played by the surrounding environment in shaping the radio morphology. In the "classical" picture, powerful FR II radio galaxies are associated to efficient accretion disks in their central engines, while less powerful FR Is to inefficient accretion flows. However, this is not a sharp one-to-one correspondence: in fact, there exist sources with radio morphologies typical of FR IIs but characterized by inefficient accretion (i.e. FR II-Low Excitation Radio Galaxies), which put the accretion-ejection connection in doubt. I will present a multi-wavelength study from radio to X-rays of these objects belonging to radio catalogs selected at high (order of Jy) radio fluxes with the aim of shedding light on their nature: do they represent an intermediate evolutionary phase between FR II and FR I, or are they a different class of sources? Finding an explanation for the existence of these cross-population objects is even more urgent in the mJy regime: indeed, the recent advent of large-area surveys (SDSS/NVSS/FIRST) in the local Universe, has revealed a more variegated picture of the Radio-Loud AGN population. This side of the Universe is dominated by the emerging class of compact FR 0s, and more interesting, about 90% of FR IIs are LERGs. The high-energy and multi-wavelength properties of these new sources will be discussed within the more general context of the accretion-ejection scenario.

Understanding the impact of massive star formation on its surroundings in Messier 8

Maitraiyee Tiwari
Max-Planck-Institut für Radioastronomie

Massive stars and massive protostars emit ultraviolet (UV) and far-UV (FUV) photons that give rise to bright HII regions and photodissociation regions (PDRs). HII regions comprise hot ionized gas irradiated by strong UV (h nu > 13.6 eV) radiation from a nearby star or from the high stellar temperatures of the massive protostars, which begin core nuclear-burning while accreting. PDRs are at the interface of these HII regions and the cold molecular cloud shielded from the illuminating star, and here the thermal and chemical processes are regulated by FUV (6 eV < h nu < 13.6 eV) photons. The study of HII regions and PDRs is the study of the structure, chemistry, thermal balance and evolution of a very important part of the interstellar medium (ISM). Using state-of-the-art telescopes: SOFIA, APEX and IRAM 30 m, we performed a large imaging survey in the IR, submillimeter and millimeter regime toward the Lagoon Nebula or Messier 8 (M8). By observing various transitions of rotationally excited species, we were able to constrain the physical conditions (temperatures and densities) of the interstellar gas responsible for their emission and explored the morphology of the region using the kinematic information provided by our observed data. We also investigated the formation process of small hydrocarbons in the high-UV flux PDR of the Lagoon Nebula and found gas-phase chemistry is responsible for the observed hydrocarbon abundances. Furthermore, we studied the embedded star forming region in the eastern region of the Lagoon Nebula, M8 east, using different diffuse and dense gas tracers. [Referees: Prof. Dr. Karl M. Menten, Prof. Dr. Pavel Kroupa, Prof. Dr. Simon Stellmer and Prof. Dr. Hubert Schorle]


Lunch Colloquium
MPIfR Robert Main


The peculiar ISM at the edge of the CMZ

Master Colloquium
Laura Ann Busch
Max-Planck-Institut für Radioastronomie

The Galactic Centre (GC) hosts a huge amount of molecular gas, which is concentrated in giant molecular clouds (GMCs) and cloud complexes in the so-called Central Molecular Zone (CMZ). At the edge of the CMZ, there are two bright cloud complexes: the 1.3 and the 1.6 complex, which are named according to their location at roughly 1.3 deg and 1.6 deg Galactic longitude, respectively. Besides typical Galactic centre gas at velocities <100 km/s, these complexes show gas components at high velocities, i.e., 150-180 km/s. Previous studies of both cloud complexes derived extremely high kinetic temperatures for this high-velocity gas of 200-300 K. So far, a heating source could not clearly be ascribed to these elevated temperatures as both sources lack active high-mass star formation and show dust temperatures of <20 K, however, ubiquitous shocks and turbulence are promising candidates. In order to shed light on physical conditions and chemical composition of this peculiar ISM, we performed excitation studies using a variety of molecules. We mapped the 1.3 and 1.6 complex in the whole 3 mm spectral window with the IRAM 30m telescope and at shorter wavelength with the APEX telescope. We investigated the morphology and derived kinetic temperatures of the gas, H2 number densities, and column densities of selected species in several positions in both complexes. Based on the results, we discussed where the high-velocity gas might come from and what is heating it. In addition, we investigated how the 1.3 and 1.6 complex might be associated with the current GC kinematics theory, in which the gas moves according to a gravitational potential induced by a central stellar bar. [Referees: Prof. Dr. Karl Menten and Prof. Dr. Pavel Kroupa]