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we have used the semi analytic models ( sams ) of somerville & primack ( 1999 ) to determine the distribution of galaxies in a dark matter halo , and the amount of cold gas in each galaxy .
the sams also contain the star formation history of each galaxy so we can explore the optical properties of the galaxies in the halos that give rise to dlas .
here we present results on the optical counterparts from the two models discussed in maller ( 1999 ) , in which we matched the kinematic data with thicker and less radially extended , or thinner , more radially extended gas disks .
we show both models here only to demonstrate that the optical properties are not highly sensitive to the details of the gas modeling .
we only refer to optical counterparts that reside in the same virialized halo that produces the dlas .
the contribution of lbgs in neighboring dark matter halos will be explored in future work , but is expected to be relatively unimportant .
the properties of the optical counterparts will place strong constraints on dlas models .
one constraint is the number of dlas with optical counterparts .
figure  [ figopt]a shows the distribution that we see in our models .
eighty percent of dlas do not have an optical counterpart with @xmath2 , while a rare five percent contain two or more such galaxies in the same halo .
lastly we show the distribution of optical impact parameter ( figure  [ figopt]b ) in our models .
the optical impact parameter is the physical distance between the line of sight to the quasar and the centroid of the light distribution of the lbg .
we obtain a broad distribution of optical impact parameter values in our model . because of the large radial extent of our gas disks , the dlas are often many stellar disk scale lengths from the center of the light distribution .
also in the mdm scenario , with many galaxies in a single halo , sometimes the galaxy bright enough to be identified as an optical counterpart is not one of the galaxies giving rise to the dlas : in this case very large separations are possible .
thus we expect the predictions about the optical impact parameter to be unique to the multiple disk model , and a useful way of distinguishing it from other models .    , s.  g. 1997 , in structure and evolution of the intergalactic medium from qso absorption line system , proceedings of the 13th iap astrophysics colloquium ( paris : editions frontieres ) , 303 , g. 1996 , , 281 , 475 maller , a.  h. 1999 , phd thesis , univ .
california , santa cruz maller , a. h. , somerville , r. s. , prochaska , j. x. & primack , j. r. 1999 , in after the dark ages : when galaxies were young , ed .
s.  holt & e.  smith ( aip press ) , 102 prochaska , j.  x. & wolfe , a.  m. 1998 , , 507 , 113 somerville , r.  s. & primack , j.  r. 1999 , , in press
previously we have shown ( maller et al , 1998 ) that the kinematics of damped lyman alpha systems ( dlas ) as measured by prochaska and wolfe ( 1998 ) can be reproduced in a multiple disk model ( mdm ) if the gaseous disks are of sufficient radial extent . here 
 we discuss this model s predictions for the relationship between dlas and lyman break galaxies ( lbgs ) , which we here take to be objects at @xmath0 brighter than @xmath1 . 
 we expect that future observations of the correlations between dlas and lbgs will provide a new data set able to discriminate between different theoretical models of the dlas . 
 djorgovski ( 1997 ) has already detected a few optical counterparts and more studies are underway .