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arXiv 1506.03085astro-ph.GAastro-ph.COastro-ph.SR
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形成致密的块状半导体

Forming Compact Massive Galaxies

Pieter G. van Dokkum, Erica June Nelson, Marijn Franx, Pascal Oesch, Ivelina Momcheva, Gabriel Brammer, Natascha M. Forster Schreiber, Rosalind E. Skelton, Kath… 展开作者

Pieter G. van Dokkum, Erica June Nelson, Marijn Franx, Pascal Oesch, Ivelina Momcheva, Gabriel Brammer, Natascha M. Forster Schreiber, Rosalind E. Skelton, Katherine E. Whitaker, Arjen van der Wel, Rachel Bezanson, Mattia Fumagalli, Garth D. Illingworth, Mariska Kriek, Joel Leja, Stijn Wuyts

摘要:

本文研究了大质量星系形成过程中的一个关键阶段:恒星形成星系向大质量(M_stars~10^11 Msun)、致密(r_e~1 kpc)静止星系的转变,这一转变发生在z~3到z~1.5之间。我们使用HST棱镜红移和广泛的测光在所有五个3D-HST/CANDELS领域,超过一倍的面积以前用于此类研究,并结合这些数据与凯克MOSFIRE和NIRSPEC光谱。我们首先确认,人口的大规模,紧凑,恒星形成星系存在于z~2,使用K波段光谱的25个这样的对象在2.0<z<2.5。它们的中值NII/Halpha比率为0.6,在SFR(tot)/SFR(Halpha)~10时高度模糊,并且具有大范围的观察到的线宽。我们推断从运动学和空间分布的H α的星系有旋转盘的电离气体是一个因素的~2比恒星分布更广泛。通过结合单个星系的测量,我们发现,运动学是一致的,从1 kpc的V_rot~500 km/s到7 kpc的V_rot~250 km/s,接近开普勒的下降,并在这个半径的总质量是由致密的恒星成分占主导地位。接下来,我们研究了致密大质量星系的祖先的大小和质量演化。尽管个别星系可能有着复杂的历史,有着致密和合并的时期,但我们表明,在d(log r_e)~ 0.3 d(log M_stars)的尺寸质量平面上,祖先星系的人口可能遵循一个简单的由内而外的增长轨迹。这种生长模式在固定的物理半径内逐渐增加恒星质量,当星系达到恒星密度或速度分散阈值时就会熄灭。正如其他的研究所显示的那样,增长模式在淬火后发生了变化,因为干合并使星系在尺寸质量平面上走上了一条相对陡峭的轨道。

英文摘要:

In this paper we study a key phase in the formation of massive galaxies: the transition of star forming galaxies into massive (M_stars~10^11 Msun), compact (r_e~1 kpc) quiescent galaxies, which takes place from z~3 to z~1.5. We use HST grism redshifts and extensive photometry in all five 3D-HST/CANDELS fields, more than doubling the area used previously for such studies, and combine these data with Keck MOSFIRE and NIRSPEC spectroscopy. We first confirm that a population of massive, compact, star forming galaxies exists at z~2, using K-band spectroscopy of 25 of these objects at 2.0<z<2.5. They have a median NII/Halpha ratio of 0.6, are highly obscured with SFR(tot)/SFR(Halpha)~10, and have a large range of observed line widths. We infer from the kinematics and spatial distribution of Halpha that the galaxies have rotating disks of ionized gas that are a factor of ~2 more extended than the stellar distribution. By combining measurements of individual galaxies, we find that the kinematics are consistent with a nearly Keplerian fall-off from V_rot~500 km/s at 1 kpc to V_rot~250 km/s at 7 kpc, and that the total mass out to this radius is dominated by the dense stellar component. Next, we study the size and mass evolution of the progenitors of compact massive galaxies. Even though individual galaxies may have had complex histories with periods of compaction and mergers, we show that the population of progenitors likely followed a simple inside-out growth track in the size-mass plane of d(log r_e) ~ 0.3 d(log M_stars). This mode of growth gradually increases the stellar mass within a fixed physical radius, and galaxies quench when they reach a stellar density or velocity dispersion threshold. As shown in other studies, the mode of growth changes after quenching, as dry mergers take the galaxies on a relatively steep track in the size-mass plane.

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