Eric Persson

Recent rapid improvements in the quality and size of near-infrared imaging array detectors have led to significant advances in several areas of astronomy. Persson is leading a group of Carnegie scientists and engineers in the development of telescope instrumentation that exploits these new devices. They have built one wide-field survey camera for the du Pont 2.5-m telescope, and are currently designing infrared instruments for the two Magellan 6.5-m telescopes at Las Campanas. The group has started a number of projects with the new camera, the most demanding of which concerns the discovery, measurement, and follow-up spectroscopy on distant galaxies -- particularly those whose properties and remote distances are such that they can only be studied at near-infrared wavelengths.

Until recently, it has been difficult to find significant numbers of these galaxies. This is solely due to technical reasons: detectors and cameras have not been large enough to cover large areas of sky. For the next several years, the Persson group will survey one square degree of sky to find and accurately measure the brightnesses of thousands of high-redshift galaxies. It will then be possible to estimate their distances and intrinsic luminosities, and study their clustering tendencies in space. Another objective of the survey is to discover large numbers of abnormal galaxies that exist at great distances. Persson and others have serendipitously found distant galaxies that emit virtually all of their energy in the infrared range. While these galaxies are fairly easy to detect in the near-infrared, they can be completely invisible in the deepest optical searches. They are so rare that prohibitively large areas of sky must be surveyed to find new examples. Preliminary spectroscopic evidence on a handful of such galaxies indicates a heterogeneous population: some are likely to be intense star-forming galaxies buried within optically opaque dust clouds, while others appear to be passively evolving objects in which star formation ceased several billion years before. These objects will be prime targets for Magellan instrumentation.

For the past 70 years, astronomers have tried to determine the distance scale of the universe. Persson and Carnegie collaborators hope to advance this field by studying newly found type Ia supernovae. These objects are widely believed to provide the key to understanding how the timescale, geometry, and mass content of the universe can be reconciled within the framework of general relativity. Type Ia supernovae are stellar explosion events, which appear to follow a well-defined development of brightness over time as they rise to a maximum luminosity and then decline. Because the intrinsic luminosities of supernovae at maximum light are essentially the same event-to-event, relative distances to their remote counterparts, observed in host galaxies billions of light years away, can be determined in a fairly straightforward manner. However, it is vital to be certain that the local supernova events are physically the same as their distant counterparts. At near-infrared wavelengths, type Ia supernova light curves appear to be very similar to one another. With the new infrared camera on the 2.5-m telescope, Persson's group will monitor the many new supernovae found each year and create a database that will calibrate distances to the remote objects.