Inaugural Lecture by Affiliated Associate Professor Jens-Kristian Krogager

We are pleased to invite you all for the Inaugural Lecture by Affiliated Associate Professor Jens-Kristian Krogager with the title: 

Dissecting Gas in Galaxies over Cosmic Time

Abstract: An important constituent of galaxies is their gas reservoir, most notably the neutral gas. The neutral gas is crucial for star formation, leading one to expect a correlation between the evolution of the average neutral gas mass density and the average star formation rate. However, over the past 10 billion years, while the average rate of star formation has dropped by about a factor of 10, the neutral gas density has not evolved much.

To understand this discrepancy, it’s essential to constrain the properties of the gas over cosmic time. Absorption spectroscopy emerges as a powerful probe of especially the neutral gas which is otherwise extremely elusive beyond the local volume. This technique provides insights into the gas between us and distant background sources, allowing precise measurements of column densities of various atomic and molecular species. Using multiple absorption sightlines, we can obtain a statistical average of the cosmic neutral gas density. Moreover we can constrain its chemical composition, offering valuable information about the cosmic star formation history. 

This talk highlights how absorption spectroscopy enables the study of neutral gas in galaxies across cosmic distances – from the Milky Way to galaxies at the “cosmic noon” and beyond. These absorption systems provide a unique perspective on the galaxy population, complementing traditional photometric studies sampling mainly the brightest tip of the iceberg – if we can understand the link between galaxies seen in absorption and emission. Lastly, I will focus on current efforts towards the first blind quasar survey, emphasizing its importance not only for understanding absorption systems but also for gaining broader insights into the evolution of quasars and galaxies.


A reception will follow to celebrate the lecture. It will be held at Aud. C. (just across the hall from Aud. A).