Bimodel Galaxy Formation Through Hierarchical Clustering --- Implications from Skeleton Tree Formalism

Details Bimodel Galaxy Formation Through Hierarchical Clustering --- Implications from Skeleton Tree Formalism Bimodel Galaxy Formation Through Hierarchical Clustering --- Implications from Skeleton Tree Formalism

Feb 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sgyu.conf..135h&link_type=abstract

Studies of Galaxies in the Young Universe with New Generation Telescope, Proceedings of Japan-German Seminar, held in Sendai, Ja

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The formation and evolution of elliptical galaxies remain a hot topic of debate. The small scatter in the color-magnitude relation for cluster E galaxies at low and high redshifts strongly supports that their stars already formed at high redshifts. Recent observed SCUBA sources are probably these starbursting E galaxies at high redshifts. This picture seems to contradict naive hierarchical clustering scenarios in which large E galaxies were formed through starburst phase induced with merging of small spirals. The extended Press-Schechter formalism, frequently used in semi-analytic modelings, cannot distinguish the episodic merging from the continuous accretion in the mass growth processes. In order to study the correct mass growth history of the halos with the distinction between merger and accretion, we formulated the skeleton tree formalism, which can reproduce the results of N-body simulations; the violent merger forms the central part of the bound halos and the late accretion produces their envelope. This mass assembly also explains the correlation between the mass of a halo and its characteristic density remarked by Navaro, Frenk, & White (1997). In ΛCDM model, we found that the merger halo formation is stopped around z=3 and the accretion growth dominates after that at the galactic mass scale. With bimodal star formation picture of intense starburst at early merger and mild star formation at late accretion, the mass growth history can explain the observed properties of E galaxies as 1) the early merger produces the old and dense homogeneous stellar component appeared in the FP and the CM relation, and 2) the late accretion produces the extended halo observed from X-ray luminous emission which is not correlated with their starlight. Furthermore, it predicts 3) the stellar disk grows at late accretion phase, and 4) the two modes of star formation were switched around z=2-3 in Λ CDM cosmology. This bimodal galaxy formation related to bimodal mass growth should be checked with A) studying the FP of gravitational lens E galaxies around z ≃ 1 with 10-m telescopes like SUBARU and B) statistics of galaxy spin and spin-density correlation with large surveys like 2dF and SDSS. The skeleton tree formalism can also supply the basic and analytical tools in the statistical analysis of those observations.

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