Pascal Oesch

Pascal received his Ph.D. in 2010 at ETH Zurich and was a Hubble Fellow at the University of California, Santa Cruz, from 2010-2013. He then moved to Yale as a YCAA Fellow until 2016, when he became an assistant professor at the University of Geneva as the group leader of the SNSF Professorship grant, “Galaxy Build-up at Cosmic Dawn.” This group’s primary focus is on understanding the build-up and assembly of the first generations of galaxies: “Our research is focused on understanding the build-up and assembly of the first generations of galaxies from a panchromatic observational study. In particular, we use deep imaging and spectroscopy from the James Webb Space Telescope, the Hubble and Spitzer Space Telescopes, in addition to ground-based follow-up with Keck, VLT, ALMA, and NOEMA. This allows us to study large samples of the galaxies and trace their mass build-up out to z~13 when the Universe was only approximately 300 million years old.”

In 2015, Pascal and colleagues used the Hubble Space Telescope to find a distant galaxy named GN-z11, which was the most distant galaxy known for half a decade. (GN stands for “Goods North,” the region of the sky in which the galaxy was seen, and “z11” indicates that it has a redshift of 11. When a galaxy is moving away from observers on Earth, its light is shifted to the red end of the spectrum.) More recently, Pascal and colleagues have used data from the recently-launched James Webb Space Telescope to find even more distant galaxies whose redshift and age are currently being analyzed.

“The galaxy GN-z11 is seen at just 400 Myr after the Big Bang, when the Universe was a mere 3% of its current age. GN-z11 reveals surprising new clues about how galaxies formed. It shows that galaxy build-up was well underway very early in cosmic history …The measurement of GN-z11 represents a huge success for the Hubble Space Telescope. It managed to find the galaxy in the first place and measure its distance accurately. The previous distance records came from galaxies found with Hubble, but then confirmed with larger aperture telescopes from the ground.”

The University of Geneva describes the team’s recent work in a press release: “The James Webb Space Telescope already delivered a new record-breaking galaxy in its first week of operations. Our team analyzed some of the first images from the NIRCam instrument and found two very luminous galaxies in one of these fields: the GLASS ERS program. The two sources, GLASS-z11 and GLASS-z13, lie at estimated redshifts of z~11 and z~13, respectively. This means they existed at a time when the Universe was a mere ~300-400 Myr old. The light of these galaxies thus had to travel for 13.4 and 13.5 billion years to reach us. Surprisingly, the two sources have already built up an estimated 1 billion solar mass in stars in a very short period of time. GLASS-z13 lies at an even larger distance than the previous record holder from HST: GN-z11.

While other candidates’ galaxies might lie at an even larger distance, this is by far the most secure source to date. However, JWST will undoubtedly discover more distant galaxies in the very near future. By pushing our observational horizon to these distant sources, we are trying to answer the big questions: when did the Universe transition from a dark to a luminous place, and when did the first galaxies ever form?”

The main focus of the team’s work now will be to exploit the new James Webb Space Telescope, which is already revolutionizing our view of early galaxies and will, for the first time, provide a complete census of the galaxy population in the very early universe. This research was made possible by support from the Swiss National Science Foundation and the State Secretariat for Education, Research, and Innovation.

SOURCES: University of Geneva, Galaxy Build-up at Cosmic Dawn, Pascal’s Website