Context :

Aims : To study chemical composition of metal-rich absorbers at high redshifts in order to understand their nature and to determine sources of their metal enrichment .

Methods : From six spectra of high- z QSOs , we select eleven metal-rich , Z \raise 1.29 pt \hbox { $ > $ \kern - 7.5 pt \raise - 4.73 pt \hbox { $ \sim$ } } Z _ { \odot } , and optically-thin to the ionizing radiation , N ( H i ) < 10 ^ { 17 } cm ^ { -2 } , absorption systems ranging between z = 1.5 and z = 2.9 and revealing lines of different ions in subsequent ionization stages .
Computations are performed using the Monte Carlo Inversion ( MCI ) procedure complemented with the adjustment of the spectral shape of the ionizing radiation .
This procedure along with selection criteria for the absorption systems guarantee the accuracy of the ionization corrections and of the derived element abundances ( C , N , O , Mg , Al , Si , Fe ) .

Results : The majority of the systems ( 10 from 11 ) show abundance patterns which relate them to outflows from low and intermediate mass stars .
One absorber is enriched prevalently by SNe II , however , a low percentage of such systems in our sample is conditioned by the selection criteria .
All systems have sub-kpc linear sizes along the line-of-sight with many less than \sim 20 pc .
In several systems , silicon is deficient , presumably due to the depletion onto dust grains in the envelopes of dust-forming stars and the subsequent gas-dust separation .
At any value of [ C/H ] , nitrogen can be either deficient , [ N/C ] < 0 , or enhanced , [ N/C ] > 0 , which supposes that the nitrogen enrichment occurs irregularly .
In some cases , the lines of Mg ii \lambda \lambda 2796 , 2803 appear to be shifted , probably as a result of an enhanced content of heavy isotopes ^ { 25 } Mg and ^ { 26 } Mg in the absorbing gas relative to the solar isotopic composition .
Seven absorbers are characterized by low mean ionization parameter U , \log U < -2.3 , among them only one system has a redshift z > 2 ( z _ { abs } = 2.5745 ) whereas all others are found at z \sim 1.8 .
This statistics is not affected by any selection criteria and reflects the real rise in number of such systems at z < 2.0 .
Comparing the space number density of metal-rich absorbers with the comoving density of star-forming galaxies at z \sim 2 , we estimate that the circumgalactic volume of each galaxy is populated by \sim 10 ^ { 7 } -10 ^ { 8 } such absorbers with total mass \raise 1.29 pt \hbox { $ < $ \kern - 7.5 pt \raise - 4.73 pt \hbox { $ \sim$ } } 1 / 100 th of the stellar galactic mass .
Possible effects of high metal content on the peak values of star-forming and AGN activities at z \sim 2 are discussed .

Conclusions :