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We use semi-analytical modelling of galaxy formation to predict the mix of elliptical galaxies with boxy and disky isophotes,
assuming they originated from major mergers of different mass ratios. Numerical simulations of merging spiral galaxies indicate
equal mass mergers leading to boxy and merger with a mass ratio of 3:1 to disky ellipticals. Assigning isophotal shapes to
elliptical galaxies in our model we find bright disky ellipticals being as frequent or more frequent as bright boxy ellipticals,
in contrast to observations which indicate that most of the bright ellipticals should be boxy. The precursors of bright ellipticals
in our model are mainly also ellipticals which merge with each other later. Assuming that the merger of two ellipticals results
in boxy ellipticals increases the fraction of bright boxy ellipticals. By defining a disky as a bulge dominated galaxy with
an additional disk mass of more than 20% the total baryonic mass, increases the fraction of low mass disky ellipticals and
reproduces the observed trend of a steep increase in the fraction of low mass disky ellipticals.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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We use semi-analytical modelling of galaxy formation to predict the mix of elliptical galaxies with boxy and disky isophotes,
assuming they originated from major mergers of different mass ratios. Numerical simulations of merging spiral galaxies indicate
equal mass mergers leading to boxy and merger with a mass ratio of 3:1 to disky ellipticals. Assigning isophotal shapes to
elliptical galaxies in our model we find bright disky ellipticals being as frequent or more frequent as bright boxy ellipticals,
in contrast to observations which indicate that most of the bright ellipticals should be boxy. The precursors of bright ellipticals
in our model are mainly also ellipticals which merge with each other later. Assuming that the merger of two ellipticals results
in boxy ellipticals increases the fraction of bright boxy ellipticals. By defining a disky as a bulge dominated galaxy with
an additional disk mass of more than20% the total baryonic mass, increases the fraction of low mass disky ellipticals and
reproduces the observed trend of a steep increase in the fraction of low mass disky ellipticals.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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David A. Wake Robert C. Nichol Daniel J. Eisenstein Jon Loveday Alastair C. Edge Russell Cannon Ian Smail Donald P. Schneider Ryan Scranton Daniel Carson Nicholas P. Ross Robert J. Brunner Matthew Colless Warrwick J. Couch Scott M. Croom Simon P. Driver José da Ângela Sebastian Jester Roberto de Propris Michael J. Drinkwater Joss Bland-Hawthorn Kevin A. Pimbblet Isaac G. Roseboom Tom Shanks Robert G. Sharp Jon Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,372(2):537-550
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S. Andreon 《Astrophysics and Space Science》2003,285(1):143-147
We studied the scatter across clusters of the color of the red sequence in are presentative and large sample of clusters (more
than 200) detected on the Early Data Release of the Sloan Digital Sky Survey (EDR-SDSS) in the redshift range 0.06<z<0.34. We found an extreme degree of homogeneity in the color of the red sequence (the intrinsic scatter is about 0.02 to 0.03
mag)suggesting that either galaxies on the red sequence formed a long time ago (z>2) or else their star formation is universally delayed with preservation of a small spread in age formation. The latter possibility
is ruled out by the mere existence of galaxies at high redshift. While the old age of ellipticals was already been claimed
for a small heterogeneous collection of clusters, most of which are rich ones, we found that it holds for a ten to one hundred
larger sample, representative of all clusters and groups detected on the EDR-SDSS. Hence, we claim the possible universality
of the color of the galaxies on the red sequence. Furthermore, the sample includes a large number of very poor clusters (also
called groups), not studied in previous works, for which the hierarchical and monolithic scenarios of elliptical formation
predict different colors for the brightest ellipticals. The observed red sequence color does not depend on cluster/group richness
at a level of 0.02 mag, while a 0.23 mag effect is expected according to the hierarchical prediction. Therefore, the stellar
population of red sequence galaxies is similar in clusters and groups, in spite of different halo histories. Finally, since
the observed rest-frame color of the red sequence does not depend on environment and redshift, it can be used as a distance
indicator, with an error σz=0.018, a few times better than the precision achieved by other photometric redshift estimates and twice better than the precision
of the Fundamental Plane for a single galaxy at the median redshift of the EDR-SDSS.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Current views consider shell structures as bona fide signatures of a recent minor/major merging event though also weak interaction models (WIM) could produce long lasting shells on host galaxies possessing a stellar thick disc.We present a B V band photometric study of a sample of 5 shell galaxies belonging to the Malin & Carter (1983) compilation. The structural properties and colors of the galaxies, as well as the colors of their shells are examined in detail. We did not find signatures of the presence of double nuclei. NGC 7585 is the only E galaxy in the sample and has a moderately boxy structure. The other galaxies have either a discy structure or are mixed E/S0 type galaxies. NGC 474 is a true lenticular. NGC 6776 shows a diffuse asymmetric outer structure and a system of tails of the the same color of the galaxy body; but not clear shells. In general, the color of the shells in our sample is similar or slightly redder than that of the host galaxy, whose color, in turn, is typical of the early‐type morphological class. One of the outer shells of NGC 474 is significantly bluer than the body of the galaxy. Since NGC 474 appears to be interacting with NGC 470, the color of this one shell could be explained as result of a recent acquisition of material through tidal interaction. The WIM hypothesis could explain both the red and the blue shells of NGC 474, this latter acquired from the fly‐by of the nearby companion NGC 470, but the lack of the constancy of shell surface brightness as a ratio of the underlying galaxy brightness argues against WIM. We speculate about evidence, which also comes from different observations, that suggests a merging/accretion origin of the shells. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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