The Build-Up of the Hubble Sequence in the COSMOS Field
P. A. Oesch, C. M. Carollo, R. Feldmann, O. Hahn, S. J. Lilly, M. T. Sargent, C. Scarlata, M. C. Aller, H. Aussel, M. Bolzonella, T. Bschorr, K. Bundy, P. Capak… 展开作者
P. A. Oesch, C. M. Carollo, R. Feldmann, O. Hahn, S. J. Lilly, M. T. Sargent, C. Scarlata, M. C. Aller, H. Aussel, M. Bolzonella, T. Bschorr, K. Bundy, P. Capak, O. Ilbert, J. -P. Kneib, A. M. Koekemoer, K. Kovac, A. Leauthaud, E. Le Floc'h, R. Massey, H. J. McCracken, L. Pozzetti, A. Renzini, J. Rhodes, M. Salvato, D. B. Sanders, N. Scoville, K. Sheth, Y. Taniguchi, D. Thompson
我们使用~ 8，600个> 5e 10 Msol的COSMOS星系来研究大质量椭圆星系、膨胀主导盘、中间膨胀盘、无膨胀盘和不规则星系的形态混合从z=0.2到z=1是如何演化的。形态演化强烈依赖于质量。在M> 3e 11 Msol时，在形态混合中没有检测到演化：自z=1起椭圆星系占主导地位，哈勃序列在这个时期已经定量地稳定下来。在1 e11 Msol质量尺度，几乎没有发现演化，这完全可以用大合并来解释。从z=1到z=0.2的大部分形态演化发生在质量为5e 10 - 1 e11 Msol的地方，其中：（i）螺旋的比例大幅下降，早期类型的贡献增加。这种增加主要是由膨胀占主导地位的磁盘的增长产生的，其贡献从z=1时的约10%变化到z=0.2时的>30%（参见图1）。椭圆部分从~15%增长到~20%）。因此，在这些质量，从晚型到早型的转变导致无盘椭圆形态，统计频率仅为30% -40%。否则，负责转换的进程会保留或产生不可忽略的磁盘组件。(ii)在z=1时，无膨胀的盘状星系占中等质量星系总数的15%，在z=0.2时几乎消失。由于z=1，合并率太低，无法解释这些巨大的无凸起圆盘的消失，这些圆盘很可能通过长期演化而增长凸起。
英文摘要：
We use ~8,600 >5e10 Msol COSMOS galaxies to study how the morphological mix of massive ellipticals, bulge-dominated disks, intermediate-bulge disks, bulge-less disks and irregular galaxies evolves from z=0.2 to z=1. The morphological evolution depends strongly on mass. At M>3e11 Msol, no evolution is detected in the morphological mix: ellipticals dominate since z=1, and the Hubble sequence has quantitatively settled down by this epoch. At the 1e11 Msol mass scale, little evolution is detected, which can be entirely explained with major mergers. Most of the morphological evolution from z=1 to z=0.2 takes place at masses 5e10 - 1e11 Msol, where: (i) The fraction of spirals substantially drops and the contribution of early-types increases. This increase is mostly produced by the growth of bulge-dominated disks, which vary their contribution from ~10% at z=1 to >30% at z=0.2 (cf. the elliptical fraction grows from ~15% to ~20%). Thus, at these masses, transformations from late- to early-types result in disk-less elliptical morphologies with a statistical frequency of only 30% - 40%. Otherwise, the processes which are responsible for the transformations either retain or produce a non-negligible disk component. (ii) The bulge-less disk galaxies, which contribute ~15% to the intermediate-mass galaxy population at z=1, virtually disappear by z=0.2. The merger rate since z=1 is too low to account for the disappearance of these massive bulge-less disks, which most likely grow a bulge via secular evolution.
