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تسجيل مستخدم جديدOn the buildup of massive early-type galaxies at z<~1. II- The coordinated key role of wet, mixed, and dry major mergers
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تأليف
M. C. Eliche-Moral
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Hierarchical models predict that present-day massive early-type galaxies (mETGs) have finished their assembly at a quite late cosmic epoch (z~0.5), conflicting directly with galaxy mass-downsizing. In Eliche-Moral et al. (2010), we presented a semi-analytical model that predicts the increase by a factor of ~2.5 observed in the number density of mETGs since z~1 to the present, just accounting for the effects of the major mergers strictly-reported by observations. Here, we describe the relative, coordinated role of wet, mixed, and dry major mergers in driving this assembly. Accordingly to observations, the model predicts that: 1) wet major mergers have controlled the mETGs buildup since z~1, although dry and mixed mergers have also contributed significantly to it; 2) the bulk of this assembly takes place during the ~1.4 Gyr time-period elapsed at 0.7<z<1, being nearly frozen at z<~0.7; 3) this frostbite can be explained just accounting for the observational decrease of the major merger fraction since z~0.7, implying that major mergers (and, in particular, dry events) have contributed negligibly to the mETGs assembly during the last ~6.3 Gyr; and 4) major mergers are responsible for doubling the stellar mass at the massive-end of the red sequence since z~1. The most striking model prediction is that at least ~87% of the mETGs existing at z~1 are not the passively-evolved, high-z counterparts of present-day mETGs, but their gas-poor progenitors instead. This implies that <~5% of present-day mETGs have been really in place since z~1. The model derives a redshift of final assembly for present-day mETGs in agreement with hierarchical models (z~0.5), reproducing at the same time the observed buildup of mETGs at z<~1.(Abridged)
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Hierarchical models predict that massive early-type galaxies (mETGs) derive from the most massive and violent merging sequences occurred in the Universe. However, the role of wet, mixed, and dry major mergers in the assembly of mETGs is questioned by
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