The highest redshift quasars

The highest redshift quasars

I have led major initiatives to observe molecular gas and dust in the first quasars located in the Epoch of Reionzation (and subsequent work). I have been leading the Pan-STARRS1 quasar search for the most distant quasars which has led to the discovery of >100 quasars at redshifts beyond z=6 (current lead at MPIA: Eduardo Banados). We have been following-up these quasars through large initiatives at NOEMA, ALMA, X-shooter, MUSE, VLA, and the VLBA.


Evolution of galaxies through cosmic times

Over the last decade, I have been studying the interstellar medium of distant galaxies through various efforts. I have been Co-PI on (A)LESS to study submillimeter galaxies in the Extended Chandra Deep Field South with LABOCA and ALMA. I am Co-PI of ASPECS, an ALMA large program that obtained unprecedented spectral line scans of the Hubble Ultra-Deep Field (see 'Projects' tab above).


The structure the interstellar medium in galaxies

Since my PhD, I have led studies to spatially resolve the interstellar medium in galaxies, both the atomic and molecular gas phase. I was PI of the THINGS survey at the VLA, and Co-PI of the follow-up HERACLES survey at the IRAM 30m to study nearby galaxies (see 'Projects' tab above). I have since been involved in many follow-up programs of nearby galaxies, including recent very high-resolution ALMA imaging of NGC 253 and NOEMA imaging of M 82.

Sub)mm/radio astronomy

(Sub)mm/radio astronomy

I am fascinated by the observational techniques to study the Universe using (sub)millimeter and radio facilities. During my first postdoc at Caltech I spent three years working for the OVRO millimeter interferometer. During my second postdoc at NRAO in Socorro, New Mexico, I intensively used the VLA, and contributed to the ALMA Test Facility. My group is a major user of the IRAM and ALMA facilities, and I serve on numerous bodies that discuss future facilities, such as the DSA-2000, the ngVLA, and future IRAM upgrades (see 'Observatories' tab above).


walter [at]




Max-Planck-Institut für Astronomy
Königstuhl 17
69117 Heidelberg