The stellar spheroid, the disk, and the dynamics of the cosmic web

Astrophysical Journal Letters 800.2 (2015): L30 reproduced by permission of the AAS
Models of the advanced stages of gravitational instability predict that baryons that form the stellar populations of current galaxies at z = 0 displayed a web-like structure at high z, as part of the cosmic web (CW). We explore details of these predictions using cosmological hydrodynamical simulations. When the stellar populations of the spheroid and disk components of simulated late-type galaxies are traced back separately to high zs we found CW-like structures where spheroid progenitors are more evolved than disk progenitors. The distinction between the corresponding stellar populations, as driven by their specific angular momentum content j, can be explained in terms of the CW evolution, extended to two processes occurring at lower z. First, the spheroid progenitors strongly lose j at collapse, which contrasts with the insignificant j loss of the disk progenitors. The second is related to the lack of alignment, at assembly, between the spheroid-to-be material and the already settled proto-disk, in contrast to the alignment of disk-to-be material, in some cases resulting from circumgalactic, disk-induced gravitational torques. The different final outcomes of these low-z processes have their origins in the different initial conditions driven by the CW dynamics
This work was partially supported by the MICINN and MINECO (Spain) through the grants AYA2009-12792-C03-02, AYA2009-12792-C03-03, and AYA2012-31101 from the PNAyA, as well as by the "Supercomputación y e-Ciencia" Consolider-Ingenio CSD2007-0050 project. A.O. was financially supported through a FPI contract from AYA2009-12792-C03-03 and C.B.B. through a contract from AYA2012-31101