  Deep surveys of the sky at millimeter wavelengths have revealed a population
of ultra-luminous infrared galaxies (ULIRGs) at high redshifts. These appear
similar to local objects of similar luminosities (such as Arp220) but are much
more ``important'' at high redshift than at low reshift, in the sense that they
represent a much larger fraction of the total luminous output of the distant
Universe than they do locally. In fact the ULIRGs at high redshift are
producing a significant fraction (>= 15%) of the total luminous output of the
Universe averaged over all wavelengths and all epochs. The high z ULIRGs could
plausibly be responsible for producing the metal-rich spheroidal components of
galaxies, including the bulges that are the subject of this conference. In this
case we would infer from the redshift distribution of the sources that much of
this activity is probably happening relatively recently at z <= 2.
