Abstract
MNRAS, 398, pp. 312-320 (2009) Using high resolution SPH simulations in a fully cosmological Lambda CDM
context we study the formation of a bright disk dominated galaxy that
originates from a "wet" major merger at z=0.8. The progenitors of the disk
galaxy are themselves disk galaxies that formed from early major mergers
between galaxies with blue colors. A substantial thin stellar disk grows
rapidly following the last major merger and the present day properties of the
final remnant are typical of early type spiral galaxies, with an i band B/D
~0.65, a disk scale length of 7.2 kpc, g-r = 0.5 mag, an HI line width
(W_{20}/2) of 238 km/sec and total magnitude i = -22.4. The key ingredients for
the formation of a dominant stellar disk component after a major merger are: i)
substantial and rapid accretion of gas through cold flows followed at late
times by cooling of gas from the hot phase, ii) supernova feedback that is able
to partially suppress star formation during mergers and iii) relative fading of
the spheroidal component. The gas fraction of the progenitors' disks does not
exceed 25% at z<3, emphasizing that the continuous supply of gas from the local
environment plays a major role in the regrowth of disks and in keeping the
galaxies blue. The results of this simulation alleviate the problem posed for
the existence of disk galaxies by the high likelihood of interactions and
mergers for galaxy sized halos at relatively low z.