Star Formation Efficiency in Nearby Galaxies
Abstract: I will present the results from ALMA-PHANGS Large Program,to study star-formation efficiency (SFE) in nearby galaxies, at the scale of giant molecular clouds in ~80 nearby galaxies. This represent the largest sample of SFE measurements to date. I will show that SFE per free-fall time is in the order of 1%. Then, I will show systematic changes that affect SFE per free-fall time among galaxies and between regions inside galaxies, including comparisons to theoretical expectation. I will close by briefly discussing the potential of the next generation VLA telescope to push this topic towards the next level of improvement.
Extreme UV Emission: Clues from Reionization-Era Analogs
Abstract: In the last few years, our first glimpse of the spectral properties of z~5-7 galaxies has emerged. Deep UV spectra have revealed prominent high-ionization nebular emission lines (i.e., C IV,He II, C III]) indicating that extreme radiation fields may be characteristic of reionization-era systems. While such strong high-ionization emission lines are atypical of the well-studied z~0-3 galaxy samples, our recent UV spectral campaigns have revealed several galaxies with analogous emission-line features to reionization-era systems. I will discuss the recent detection of extremely strong UV emission in nearby galaxies and the potential sources of their very hard ionizing radiation fields. Such strong detections of high-ionization emission lines have been linked to the leakage of Lyman continuum (LyC) photons (necessary for reionization) both theoretically and observationally. These extreme UV emission-lined warf galaxies provide a template for the extreme conditions that are important for reionization and suggest new diagnostics that will be accessible with extremely large telescopes (ELTs) and could identify these targets in the distant universe.
Special Speaker at 3pm:
Krijn de Vries
From Cherenkov to Transition radiation
Abstract: Both Cherenkov effects as well as transition radiation can intuitively be understood from the basic geometrical relation between the position where a signal is emitted and the time when it arrives at the observer. It follows that both effects apply equally well to a net charge, as to a net (charge-neutral) current. These concepts are applied to understand the coherent radio emission from a high-energy particle cascade moving through different media.