Kathryn V Johnston's WWW site

Research Interests

I am interested in studying the formation of galaxies by looking at our own Milky Way, together with nearby galaxies in the Local Group. It is believed that these objects through the gradual agglomeration of many smaller dwarf galaxies. Much of my research looks at this process of hierarchical structure formation.

The Life and death of satellite galaxies

During my graduate student days (1991-1996 at UC Santa Cruz), I investigated what would happen as a single satellite galaxy is torn apart by tidal forces from the parent galaxy it is orbiting. Numerical modelling revealed that debris torn from the smaller galaxy could form streams of stars both leading and trailing the satellite along its orbit. I was lucky that, coincident to this theoretical work, a satellite in the middle of being cannibalized by the Milky Way was discovered (the Sagittarius dwarf galaxy) with structure curiously reminiscent of the simulations.

The Milky Way as a Cannibal

As a postdoc at the Institute for Advanced Study (1996-1999) I worked with observational colleagues to model debris from satellite destruction as it was discovered, and to understand how it could be used. Because of the simple dynamics of tidal debris it seems to be a powerul probe not only of the destroyed satellites history (mass, mass-loss rate and orbit), but also of size, shape and lumpiness of the parent galaxy it is orbiting.

Does the Local Group make sense?

In the last decade increases in the scope and sensitivity of observaitons around our own Milky Way Galaxy and the nearest neaighboring galaxy (Andromeda) have revealed many indications of debris from satellite destruction. With James Bullock (UC Irvine) I have constructed models of the outskirts of galaxies like this built from the destructure of many satellites. Analyses of these simulations and comparison to observations should tell us more about the objects from which they were actually formed.

What's missing from this picture?

While a postdoc with me at Wesleyan University Andreea Font worked has worked with the Johnston/Bullock models to add extra dimensions of chemical composition. This refinement is proving invaluable for comparison with current and future observations.


Kathryn V Johnston Department of Astronomy Columbia University Home Research Teaching	Research Interests I am interested in studying the formation of galaxies by looking at our own Milky Way, together with nearby galaxies in the Local Group. It is believed that these objects through the gradual agglomeration of many smaller dwarf galaxies. Much of my research looks at this process of hierarchical structure formation. The Life and death of satellite galaxies During my graduate student days (1991-1996 at UC Santa Cruz), I investigated what would happen as a single satellite galaxy is torn apart by tidal forces from the parent galaxy it is orbiting. Numerical modelling revealed that debris torn from the smaller galaxy could form streams of stars both leading and trailing the satellite along its orbit. I was lucky that, coincident to this theoretical work, a satellite in the middle of being cannibalized by the Milky Way was discovered (the Sagittarius dwarf galaxy) with structure curiously reminiscent of the simulations. The Milky Way as a Cannibal As a postdoc at the Institute for Advanced Study (1996-1999) I worked with observational colleagues to model debris from satellite destruction as it was discovered, and to understand how it could be used. Because of the simple dynamics of tidal debris it seems to be a powerul probe not only of the destroyed satellites history (mass, mass-loss rate and orbit), but also of size, shape and lumpiness of the parent galaxy it is orbiting. Does the Local Group make sense? In the last decade increases in the scope and sensitivity of observaitons around our own Milky Way Galaxy and the nearest neaighboring galaxy (Andromeda) have revealed many indications of debris from satellite destruction. With James Bullock (UC Irvine) I have constructed models of the outskirts of galaxies like this built from the destructure of many satellites. Analyses of these simulations and comparison to observations should tell us more about the objects from which they were actually formed. What's missing from this picture? While a postdoc with me at Wesleyan University Andreea Font worked has worked with the Johnston/Bullock models to add extra dimensions of chemical composition. This refinement is proving invaluable for comparison with current and future observations.