By making use of Herschel -PEP observations of the COSMOS and Extended Groth Strip fields , we have estimated the dependence of the clustering properties of FIR-selected sources on their 100 \mu m fluxes .
Our analysis shows a tendency for the clustering strength to decrease with limiting fluxes .
By assuming a power-law slope with \gamma = 1.8 for the two-point correlation function \xi ( r ) = ( r / r _ { 0 } ) ^ { - \gamma } , we find : r _ { 0 } ( S _ { 100 \mum } \geq 8 mJy ) = 4.3 ^ { +0.7 } _ { -0.7 } Mpc and r _ { 0 } ( S _ { 100 \mum } \geq 5 mJy ) = 5.8 ^ { +1.8 } _ { -2.0 } .
These values convert into minimum halo masses M _ { min } \sim 10 ^ { 11.6 } M _ { \odot } for sources brighter than 8 mJy and M _ { min } \sim 10 ^ { 12.4 } M _ { \odot } for fainter , S _ { 100 \mum } \geq 5 mJy galaxies .
We show such an increase of the clustering strength to be due to an intervening population of z \sim 2 sources , which are very strongly clustered and whose relative contribution , equal to about 10 % of the total counts at S _ { 100 \mum } \geq 2 mJy , rapidly decreases for brighter flux cuts .
By removing such a contribution , we find that z \mathrel { \hbox to 0.0 pt { \lower 3.0 pt \hbox { $ \sim$ } } \raise 2.0 pt \hbox { $ < $ } } 1 FIR galaxies have approximately the same clustering properties , irrespective of their flux level .
The above results were then used to investigate the intrinsic dependence on cosmic epoch of the clustering strength of dusty star-forming galaxies between z \sim 0 and z \sim 2.5 .
This was done by comparing our dataset with IRAS in the local universe and with sources selected at 160 \mu m in the GOODS-South at z \simeq 2 .
In order to remove any bias in the selection process , the adopted sample only includes galaxies observed at the same rest-frame wavelength , \lambda \sim 60 \mu m , which have comparable luminosities and therefore star-formation rates ( SFR \mathrel { \hbox to 0.0 pt { \lower 3.0 pt \hbox { $ \sim$ } } \raise 2.0 pt \hbox { $ > $ } } 100 M _ { \odot } /yr ) .
Our analysis shows that the same amount of ( intense ) star forming activity takes place in extremely different environments at the different cosmological epochs . For z \mathrel { \hbox to 0.0 pt { \lower 3.0 pt \hbox { $ \sim$ } } \raise 2.0 pt \hbox { $ < $ } } 1 the hosts of such star forming systems are small , M _ { min } \sim 10 ^ { 11 } M _ { \odot } , isolated galaxies .
High ( z \sim 2 ) redshift star formation instead seems to uniquely take place in extremely massive/cluster-like halos , M _ { min } \sim 10 ^ { 13.5 } M _ { \odot } , which are associated with the highest peaks of the density fluctuation field at those epochs .