RAY WEYMANN --- OCIW

"THE EVOLUTION OF THE LOW REDSHIFT LYMAN ALPHA FOREST"


AN ANALYSIS OF THE RATE OF EVOLUTION OF THE LYMAN ALPHA FOREST IN
THE REDSHIFT INTERVAL 0 TO 1.5, BASED UPON THE HST QUASAR ABSORPTION
LINE KEY PROJECT DATA WILL BE PRESENTED. THE RATE OF EVOLUTION IS
VERY MUCH FLATTER THAN AT HIGH REDSHIFT AND THE TRANSITION TO THE
STEEPER RATE AT HIGHER REDSHIFTS SEEMS TO BE QUITE SUDDEN. HOWEVER,
THE RATE SEEMS TO BE COLUMN DENSITY-DEPENDENT, WITH THE HIGHER
COLUMN DENSITY LINES EVOLVING MORE RAPIDLY. IN PARTICULAR, SYSTEMS
IN WHICH WE DETECT HEAVY ELEMENT IONS EVOLVE MUCH MORE RAPIDLY.
THESE RESULTS ARE IN AT LEAST QUALITATIVE
ACCORD WITH RECENT NUMERICAL SIMULATIONS AND AN IMPORTANT INGREDIENT
IN THIS BEHAVIOR IS THE RAPID CHANGE IN THE BACKGROUND RADIATION FIELD.
WE COMMENT BRIEFLY ON THE IMPLICATIONS OF THESE RESULTS FOR GALAXY-LY ALPHA
CLOUD ASSOCIATIONS.