Congratulations to Francesca Bonanomi on her successful PhD defense!

Congratulations to Francesca Bonanomi on her successful PhD defense!

Disentangling the interstellar spiderweb

Space between stars is far from empty: it is permeated by dust, gas, and radiation. Gas and dust are not distributed randomly, but form filaments on very different scales. These filaments may resemble parts of a spiderweb, linking the cores where stars form to their parent molecular clouds. Why do they take this shape? How do filaments form and evolve? These are still open questions that Dr. Francesca Bonanomi addressed in her PhD research.

The clearest culprit for such behavior is turbulence, which naturally creates hierarchical structures resembling fractals. To study the smallest scales at the bottom of the turbulent cascade, high-resolution observations are needed to resolve parsec-scale* filaments. Interferometric observations, which can achieve this, are severely affected by spatial filtering and lack of information at large scales. To recover the true sky emission, it is necessary to combine interferometric observations with additional data from single dish telescopes that provide "short spacing" information.

The EMERGE Early ALMA survey observed seven prototypical regions in Orion with the Atacama Large Millimeter Array (ALMA) and with the single-dish IRAM-30m telescope, resolving the gas structure down to ∼2000 astronomical units. The first goal was to quantify the impact of spatial filtering on ALMA observations and to explore data combination techniques in order to develop a routine for combining EMERGE maps. After assessing the quality of the observations, a more efficient scheduling strategy and an offline beam-reshaping routing were proposed to improve data quality prior to combination with single-dish observations.

After overcoming this first technical challenge and recovering high-quality observations, Francesca moved on to studying them. These data reveal a plethora of sub-filaments known as fibers. Fibers are the first subsonic structures formed within turbulent molecular clouds; therefore, they must originate at scales where turbulent motions dissipate. By studying the diffuse gas traced by HNC (1-0) in the EMERGE sample, Francesca analyzed its kinematics to understand the role of turbulence in the formation and evolution of fibers. She found that diffuse gas is, overall, more turbulent than dense structures, with a transition to coherence occurring at fiber scales. Moreover, high-shear regions associated with enhanced turbulence dissipation were found in close proximity to many of these dense fibers, consistent with turbulence being dissipated during the fiber formation.

With her research, Francesca Bonanomi contributed to piecing together the puzzle of the formation and evolution of the filamentary structure of the interstellar medium.

My doctoral studies have significantly contributed to my growth, both as a researcher and as an individual. I am deeply grateful for the opportunity to work in the stimulating and supportive environment of the Institute of Astrophysics in Vienna and to collaborate with such inspiring colleagues, particularly within my research group.

*Parsec – a unit used in astronomy to measure distances. One parsec is equal to 3.26 light-years.

**Astronomical unit – a unit used in astronomy to measure distances. One AU is equal to the distance between the Earth and the Sun, i.e. approximately 150 million kilometers.