Cosmic dichotomy in the hosts of rapidly star-forming systems at low and high redshifts

This paper presents a compilation of clustering results taken from the literature for galaxies with highly enhanced (SFR ~= [30-103] M&sun; yr-1) star formation activity observed in the redshift range z = [0-3]. We show that, irrespective of the selection technique and only very mildly depending on the star-forming rate, the clustering lengths of these objects present a sharp increase of about a factor 3 between z ˜ 1 and z ˜ 2, going from values of ˜5 Mpc to about 15 Mpc and higher. This behaviour is reflected in the trend of the masses of the dark matter hosts of star-forming galaxies which increase from ˜1011.5 to ˜1013.5 M&sun; between z ˜ 1 and z ˜ 2. Our analysis shows that galaxies which actively form stars at high redshifts are not the same population of sources we observe in the more local universe. In fact, vigorous star formation in the early universe is hosted by very massive structures, while for z ≲ 1 a comparable activity is encountered in much smaller systems, consistent with the downsizing scenario. The available clustering data can hardly be reconciled with merging as the main trigger for intense star formation activity at high redshifts. We further argue that, after a characteristic time-scale of ˜1 Gyr, massive star-forming galaxies at z ≳ 2 evolve into z ≲ 1.5 passive galaxies with large (M* ~= [1011-1012] M&sun;) stellar masses.