The Herschel-PEP survey: evidence for downsizing in the hosts of dusty
  star-forming systems
  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 100um fluxes. Our analysis shows a tendency for
the clustering strength to decrease with limiting fluxes: r0(S100um >8 mJy)~4.3
Mpc and r0(S100um >5 mJy)~5.8 Mpc. These values convert into minimum halo
masses Mmin~10^{11.6} Msun for sources brighter than 8 mJy and Mmin~10^{12.4}
Msun for S100um > 5 mJy galaxies. We show such an increase of the clustering
strength to be due to an intervening population of z~2 sources, which are very
strongly clustered and whose relative contribution, equal to about 10% of the
total counts at S100um > 2 mJy, rapidly decreases for brighter flux cuts. By
removing such a contribution, we find that z <~ 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~0 and z~2.5. In order to remove any bias in the selection process, the
adopted sample only includes galaxies observed at the same rest-frame
wavelength, lambda~60 um, which have comparable luminosities and therefore
star-formation rates (SFR>~100 Msun/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<~1 the hosts of such
star forming systems are small, Mmin~10^{11} Msun, isolated galaxies. High
(z~2) redshift star formation instead seems to uniquely take place in extremely
massive/cluster-like halos, Mmin~10^{13.5} Msun, which are associated with the
highest peaks of the density fluctuation field at those epochs. (abridged)
