I'm a staff member
(Associate Professor)
at the Kapteyn Astronomical
Institute at the Rijksuniversiteit Groningen. Previously I was a
Carnegie Fellow and a Hubble Fellow at the
Observatories of the Carnegie
Institution of Washington (OCIW) and a graduate student at Lick Observatory.
My research focuses on the formation and evolution of the most massive galaxies in the Universe, especially "old, red, dead" galaxies such as elliptical and lenticular galaxies. I collaborate with members of the COMBO-17 and GEMS teams to obtain and analyze ultradeep spectroscopy of massive galaxies at intermediate redshifts to understand their evolution. Other current projects include studies of the stellar populations of nearby and distant cluster galaxies (with Sandra Faber, Alan Dressler, and Bianca Poggianti), stellar populations and gas content of local gas-rich early-type galaxies (with Paolo Serra and Thijs van der Hulst at Kapteyn Astronomical Institute, Tom Oosterloo and Raffaella Morganti at ASTRON, Elaine Sadler at University of Syndey, and Jacqueline van Gorkom at Columbia University), the stellar content of the only elliptical galaxy in the Local Group, M32 (with Tod Lauer, Wendy Freedman, Alan Dressler, Ken Mighell, and Carl Grillmair), and next-generation stellar population models (with Guy Worthey at Washington State University, Bryan Chaboyer at Dartmouth University, and Eddie Baron at University of Oklahoma). Older projects include the largest catalog of Galactic globular-cluster surface-brightness profiles to date.
Spring 2003: Formation
and evolution of galaxies
Spring 2004: Stellar
structure and evolution
Fall 2004: NOVA
Fall School 2004: Galaxies
Spring 2005: Formation
and evolution of galaxies
Spring 2006: Stellar
structure and evolution
Spring 2007: Formation
and evolution of galaxies
Fall 2007: Astronomical
Observing Techniques
Fall 2008: Stellar
structure and evolution
Spring 2009: Astronomical
Observing Techniques
Fall 2009: Sterrenstelsels
en Kosmos (Galaxies and the Universe)
The IDS sample of absorption-line data on more than 400 elliptical galaxies has been published. Tables and the Lick/IDS spectral database (both stars and galaxies) can be retrieved here.
Paper
1, on the sample of nearby elliptical galaxies, and Paper
2, on the analysis of their stellar populations, have been
published in the Astronomical
Journal.
Currently I'm studying the stellar populations of early-type (both
elliptical and lenticular) galaxies in a variety of different
environments: in low-density groups of galaxies (with Dan Kelson at OCIW), in
spiral-rich, moderate-density clusters like the Hydra Cluster, and in
rich, early-type dominated clusters like the Coma Cluster (with Sandy
Faber at UCO/Lick and Alan Dressler at OCIW) and Abell 3558.
In collaboration with S. M. Faber and A. Dressler, I am studying the stellar populations of galaxies in distant clusters of galaxies. These galaxies existed when the Universe was only half or a third of its current age. We are using both the Hubble Space Telescope and the Keck Telescope on these clusters to get both ultra-deep, ultra-high-resolution imaging and spectroscopy in our effort to understand the evolution of galaxies throughout the history of the Universe.
All of the pictures on this page are images from theHubble Space Telescope. They are galaxies in a cluster seen at a time halfway back to the Big Bang. Each box is about 175 thousand light-years across (if you were standing on a galaxy in the cluster), which is about 1 trillion trillion miles (yes, that's trillion twice), if you think in those sorts of units. Galaxies are big. But because they're so far away, they look really small---that's why we need theSpace Telescope. Details like spiral arms, bars, and ring shapes have never been seen before at such huge distances.
A poster was presented on morphological aspects of this work at the January 1995 American Astronomical Society meeting in Tuscon, Arizona, and another, at IAU Symposium 171, "New Light on Galaxy Evolution," held in Heidelberg, Germany, in June 1995.
We have now extended our study of the stellar population of ellipticals (above) to these very distant galaxies. Check out Chapters 4 and 5 of my dissertation, and look for forthcoming preprints here.
I've also been collaborating on a project to study the X-ray selected population of "hidden" AGN in intermediate-redshift clusters with Paul Martini, Dan Kelson, and John Mulchaey (all at OCIW). You can read our recent paper, the press release, or a BBC News story about our initial discoveries.
We have discovered extremely distant examples of radio-quiet, non-quasar galaxies---three objects with redshiftsz=4. This is very distant---we see these objects about 80-90% of the way back in time to the Big Bang, or about 12 billion light years away (depending on how old you think the Universe is). Two of these objects (DG 353 and P1/P2) are most likely multiple images of a common source galaxy being gravitationally lensedby the rich cluster of galaxies (the big, bright galaxies you see scattered around the image), which are still very far away---about 4 billion light years away. These very distant galaxies contain the some of the most distant stars yet discovered---meaning, of course, the earliest stars anybody has yet seen, born probably not more than a billion or two years after the Big Bang. Check out the published version.