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Bulges, often identified with the spheroidal component of a galaxy,have a complex pedigree. Massive bulges are generally red
and old,but lower mass bulges have broader dispersions in color that may becorrelated with disk colors. This suggests different
formationscenarios. I will review possible formation sequences for bulges,describe the various signatures that distinguish
these scenarios, anddiscuss implications for the high redshift universe.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The optical-IR images of the northern and southern Hubble Deep Fields are used to measure the spectral and density evolution of early-type galaxies. The mean spectral energy distribution is found to evolve passively toward a mid-F star-dominated spectrum by z approximately 2, becoming more sharply peaked around the 4000 ? break. We demonstrate with realistic simulations that hotter elliptical galaxies would be readily visible if evolution progressed blueward and brightward at z>2, following a standard initial mass function (IMF). The color distributions are best fitted by a "red" IMF, deficient above approximately 2 M middle dot in circle and with a spread of formation in the range 1.51 results from a selection bias against distant red galaxies in the optical, where the flux is too weak for morphological classification, but is remedied with relatively modest IR exposures that reveal a roughly constant space density to z approximately 2, with 32 and 16 elliptical galaxies detected above and below z=1, respectively. We point out that the lack of high-mass star formation inferred here and the requirement of metals implicates cooling flows of preenriched gas in the creation of the stellar content of spheroidal galaxies. Deep-field X-ray images will be very helpful in examining this possibility. 相似文献
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Roderik A. Overzier Qi Guo Guinevere Kauffmann Gabriella De Lucia Rychard Bouwens Gerard Lemson 《Monthly notices of the Royal Astronomical Society》2009,394(2):577-594
Motivated by recent observational studies of the environment of z ∼ 6 QSOs, we have used the Millennium Run (MR) simulations to construct a very large (∼4°× 4°) mock redshift survey of star-forming galaxies at z ∼ 6 . We use this simulated survey to study the relation between density enhancements in the distribution of i 775 -dropouts and Lyα emitters, and their relation to the most massive haloes and protocluster regions at z ∼ 6 . Our simulation predicts significant variations in surface density across the sky with some voids and filaments extending over scales of 1°, much larger than probed by current surveys. Approximately one-third of all z ∼ 6 haloes hosting i -dropouts brighter than z = 26.5 mag (≈ M *UV, z =6 ) become part of z = 0 galaxy clusters. i -dropouts associated with protocluster regions are found in regions where the surface density is enhanced on scales ranging from a few to several tens of arcminutes on the sky. We analyse two structures of i -dropouts and Lyα emitters observed with the Subaru Telescope and show that these structures must be the seeds of massive clusters in formation. In striking contrast, six z ∼ 6 QSO fields observed with Hubble Space Telescope show no significant enhancements in their i 775 -dropout number counts. With the present data, we cannot rule out the QSOs being hosted by the most massive haloes. However, neither can we confirm this widely used assumption. We conclude by giving detailed recommendations for the interpretation and planning of observations by current and future ground- and space-based instruments that will shed new light on questions related to the large-scale structure at z ∼ 6 . 相似文献
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