At redshifts larger than 2 , a large fraction ( 80 % ) of the metals are apparently yet undetected .
We use a sample of sub-mm selected galaxies ( SMGs ) with molecular gas and dynamical mass measurements from the literature to put constraints on the contribution of such galaxies to the total metal budget .
Compared to Lyman break galaxies ( LBGs ) , for example , SMGs are rarer ( by a factor of 10 or more ) , but contain much more gas and are more metal rich .
For SMGs brighter than 3 mJy , we estimate that SMGs contain only \la 9 % of the metals when we combine the observed dynamical masses ( < M _ { dyn } > \sim few \times 10 ^ { 11 } M _ { \odot } ) , number density ( n \simeq 10 ^ { -4 } Mpc ^ { -3 } ) , observed gas metallicity ( Z \simeq 1–2 Z _ { \odot } ) , and observed gas fractions ( f _ { gas } \approx 40 % ) assuming a molecular to neutral hydrogen ratio of 1 .
Including SMGs fainter than 3 mJy , we estimate that SMGs contain about \leq 15 % of the metals , where our incompleteness correction is estimated from the dust mass function .
Our results are strong upper limits given that high gas fractions and high overall metallicity are mutually exclusive .
In summary , SMGs make a significant contribution to the metal budget ( \la 15 % ) but not sufficient to solve the ‘ missing metals problem ’ .
A consequence of our results is that SMGs can only add \approx 3.5 % to \Omega _ { DLA } , and can not be the source of a significant population of dusty DLAs .