Jörn Rossa (often spelled Joern Rossa) passed away on September 19, 2009 at the young age of 40 in Mainz, Germany from a virulent fast-acting blood cancer. He was born in that same city on March 17, 1969 to Alfred and Gudrun Rossa, who survive their only child.
Joern had a deep, lifelong love of astronomy, as evidenced by the handwritten letters he wrote in his youth to prominent astronomers and astronauts for their perspectives, signatures and reprints, the popular astronomy magazines which he collected for decades, the decision to abandon a career as a locomotive driver and relearn the math and physics required to pursue his passion, the many papers he published himself, and the numerous space shuttle launches he made a point to personally attend at Kennedy Space Center. Since High School, Joern carried out observations using his own telescope, traveled with friends to remote locations to practice "serious" astrophotography, and lectured at a local amateur club.
After attaining his undergraduate degree at the University of Heidelberg (Germany) in 1996, Joern continued his education at the Ruhr-University Bochum in Germany, where he worked under the guidance of Ralf-Juergen Dettmar. He received his Ph.D. degree in 2001 with a thesis focusing on extraplanar diffuse ionized gas and dust in the halos of edge-on spiral galaxies. He performed the largest-to-this-day ground-based H-alpha survey of a large number of galaxies, quantified their extraplanar ISM, and correlated its properties with the starburst activity in the galaxy disk. After his graduation, Joern stayed in Bochum for another year as a Postdoctoral Associate. During this time he expanded his interests in the same general subject area through the use of X-ray (XMM, Chandra) and radio observations. His interest in the ISM of nearby galaxies continued through his subsequent postdoctoral career. He analyzed high-spatial resolution Hubble Space Telescope (HST) WFPC2 H-alpha data of the edge-on non-starburst spiral galaxy NGC 891. The data revealed for the first time super-thin filaments, which may indicate an important role of the magnetic fields in the gas and for mass transfer. He then received time with HST/ACS to study four other galaxies to greater depth and resolution. Joern also obtained narrow-band imaging data at Calar Alto Observatory of a sample of Seyfert galaxies, and he supervised a summer student at STScI on the analysis of this sample. Joern's observational work in these areas led to a better understanding of the physical processes that drive gas out of galaxy disks.
After his appointment in Bochum, Joern moved to the Space Telescope Science Institute (STScI) in 2002 in Baltimore, where he worked for four years as a postdoctoral researcher with Roeland van der Marel. During this time he studied and analyzed two different sets of HST data. The first project dealt with the nature of nuclear star clusters found in the centers of spiral galaxies. To study the physical properties of these clusters (e.g., masses, stellar population ages, etc.) and their formation mechanisms, spectra were obtained with HST/STIS of a sample of nuclear clusters in spiral galaxies of various Hubble types. Joern analyzed and interpreted the data, which led to the realization that the stellar populations of these nuclear clusters are often young -- indicating still on-going star formation processes -- and that the cluster mass correlates with bulge mass in a similar fashion as does the mass of supermassive black holes. The second focus of Joern's work at STScI was the nuclear properties of merger remnants. He used HST/NICMOS to obtain near-IR images and optical spectroscopy of the merging galaxies in the Toomre sequence. The near-IR images penetrate the dusty parts of these galaxies and allowed measurement of the surface brightness profiles down to scales of order 0.1 arcsec. The steepness of the brightness profiles was found to be consistent with scenarios in which merger remnants evolve into ellipticals.
Joern then moved to the University of Florida (UF) in 2006 to work as a core team member of the Flamingos 2 Extra-Galactic Survey. This survey aims at deriving the star formation histories, masses and metallicities of star formation galaxies at redshifts between 2.0-2.5 and also at deriving the properties (e.g., black hole masses) of AGN and at studying the optically obscured AGN at intermediate to high redshifts (z > 1.5). Joern was largely responsible for the target selection strategies for both samples (star-forming galaxies and AGN), for coordinating the weekly group meetings, and for designing a web-page for the extragalactic group. He was interested in using the survey to answer several cosmological questions in collaboration with Vicki Sarajedini, Rafael Guzmän, Fred Hamann, Anthony Gonzalez, the Flamingos-2 instrument PI, Stephen Eikenberry (all from UF), and with additional collaborators from the Complutense University of Madrid, Spain. Joern also worked with Vicki Sarajedini on SED fitting of variability-selected AGN in the Chandra Deep Field South. Joern was a very versatile observer, complementing his belief that understanding of the star-formation activity in galaxies can be only achieved through a multi-wavelength study of various galaxy types.
In addition to research, Joern had a strong desire to be involved in the logistical aspects of science. At STScI he participated in the support group for the time allocation committee and at UF he was the postdoctoral representative of the space allocation committee. He photographed the UF staff for the departmental webpage and was a designated photographer at a local conference and other events. He also participated in the public Museum nights at UF. He was always eager to provide his feedback on the scientific and practical issues of astronomy and filled in many surveys distributed to the astronomical community.
His colleagues and friends could always count on Joern to be extremely responsive, punctual, organized, polite and truthful; he did not tolerate false flattery and he held strongly to his own beliefs. Joern ardently loved his family and was faithful to his friends. Joern had several passions outside of astronomy. Among these were music, travel, snorkeling and photography. He played guitar and idolized Fleetwood Mac, The Eagles, and Tom Petty, among many other artists. While visiting 45 U.S. States and many other countries, Joern had a knack for picking up languages and spoke impeccable English.
We will miss Joern, a loyal son, friend and colleague.
Acknowledgments: Ralf Hahn, Nadya Gorlova, Seppo Laine and Roeland van der Marel provided crucial information, perspectives and memories needed for the foundation of this obituary; Ralf-Juergen Dettmar, Maria-Cruz Gälvez-Ortiz, Maren Hempel and Stefan Kautsch provided advice and support which helped complete the obituary; the photograph is courtesy of Nadya Gorlova.