Nicolas Lehner

Research Assistant Professor,
Astrophysics

Research Interests

My research is focused on the gaseous matter from the outskirts of our own Solar System to the largest scale structures of the Universe. The space between stars is not empty, but is filled with a tenuous amount of gas and dust, which makes up the interstellar medium (ISM). Likewise, the vast regions between galaxies and groups of galaxies are not empty. The tenuous gas in these regions, made up primarily of hydrogen, helium, and a very small amount of metals, is called the intergalactic medium (IGM). Most of the interstellar metals and dust originates from the death of stars which either exploded or blew off their outer layers, returning their material to interstellar space. This material is recycled when new stars are formed from it. On the largest scales, most of the observable matter is actually not in galaxies, but in the IGM. Studying the tenuous regions between stars and galaxies from the Milky Way to the most distant regions of the Universe is therefore crucial to an understanding of the evolution and energetics of the IGM and galaxies and their relationships through cosmic time.

The study of intergalactic absorbers observed in the spectra of distant QSOs, including the Lyman limit and damped  Lya systems that are likely connected to galaxies and their outskirts, has yielded a wealth of astrophysical and cosmological information over 90% of the age of the Universe. My current program involves observations of the IGM and young galaxies with FUSE, Hubble, Keck, and newer observatories such as GALEX and the LBT, in order to study the kinematical relationships between these absorbers and galaxies, the baryon contents and metal abundances of the IGM and galaxies at various redshifts, and the feedback mechanisms between the galaxies and IGM.

Understanding how the ISM evolves and the galaxy-IGM connection in our neighborhood where detailed information can be gained  is crucial to understanding feedback processes in the more distant Universe. I use the Hubble and Spitzer Space Telescopes to study the physical properties and evolution of the gas in our Milky Way and other nearby galaxies. These observations provide a better picture of how the gaseous disks of galaxies may evolve and how galaxies interact with the intergalactic medium.

Selected Publications

"Highly Ionized Plasma in the Large Magellanic Cloud: Evidence for Outflows and a Possible Galactic Wind," Lehner, N., Howk, J.C., 2007, MNRAS, in press (astro-ph/0702427)

"Physical Properties, Baryon Content, and Evolution of the Forest: New Insights from High Resolution Observations at  z <0.4,"  Lehner, N., Savage, B.D., Wakker, B.P., Sembach, K.R., Tripp, T.M., 2007, ApJ, in press (astro-ph/0612275)

 "Properties of the O VI Absorption  in the Local Interstellar Medium," Savage, B.D., Lehner, N., 2006, ApJS, 162, 134

"Detection of Ne VIII in the Low-Redshift Warm-Hot IGM," Savage, B.D., Lehner, N., Wakker, B.P., Sembach, K.R., Tripp, T.M., 2005, ApJ, 626, 776

"C II Radiative Cooling of the Diffuse Gas in the Milky Way," Lehner, N., Wakker, B.P., Savage, B.D, 2004, ApJ 615, 767

"FUSE Survey of the Local Interstellar Medium within 200 Parsec," Lehner, N., Jenkins, E.B., Gry, C., Moos, H.W., Chayer, P., Lacour, S., 2003, ApJ, 595, 858

Full curriculum vitae (pdf)
Please contact physics@nd.edu if a html or other version is needed.