THE COSMOLOGICAL SIZE AND VELOCITY DISPERSION EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES
THE COSMOLOGICAL SIZE AND VELOCITY DISPERSION EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES
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DOI：
10.1088/0004-637x/744/1/63
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发表时间：
2011-06
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影响因子：
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通讯作者：
L. Oser;T. Naab;J. Ostriker;P. Johansson
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作者：
L. Oser;T. Naab;J. Ostriker;P. Johansson
我们分析了目前恒星质量为M* > 6.3 × 1010 M☉的单个大质量星系的40个宇宙学重新模拟，以研究自红移z≈2以来观测到的星系大小的强烈增加和恒星速度色散的减少的物理起源。目前，40个星系中有25个处于静止状态，其结构参数（大小和速度色散）与本地早型星系一致。在z = 2时，所有M* > 1011 M☉的模拟星系（40个星系中的11个）在z = 2时都是紧实的，投射的半质量半径约为0.77（±0.24）kpc，视距色散在投射的半质量半径约为262（±28）km s - 1内（11个星系中有3个已经静止）。与观测到的高红移致密早型星系类似，模拟星系明显偏离了局部质量尺寸和质量速度色散关系。在红移为零时，尺寸增加了约5-6倍，在R1/2∝(1 + z)α之后，静止星系的α = - 1.44（所有星系的α = - 1.12）。从z≈2开始，速度色散随σ1/2∝(1 + z)β下降约1/ 3，静止星系的β = 0.44（所有星系的β = 0.37）。模拟的大小和色散演化与观测和随后的恒星系统吸积和合并的结果很好地吻合，这是分层结构形成的自然结果。相当数量的模拟大质量星系（40个星系中有7个）经历的合并质量不超过1:4（通常被认为是主要合并）。平均而言，主要的吸积模式是恒星的小合并，质量加权质量比为1:5。因此，我们得出结论，自z≈2以来的大质量早期型星系的演化及其今天的性质主要是由频繁的中等质量比的“小”合并决定的，而不仅仅是大合并。
We analyze 40 cosmological re-simulations of individual massive galaxies with present-day stellar masses of M* > 6.3 × 1010 M☉ in order to investigate the physical origin of the observed strong increase in galaxy sizes and the decrease of the stellar velocity dispersions since redshift z ≈ 2. At present 25 out of 40 galaxies are quiescent with structural parameters (sizes and velocity dispersions) in agreement with local early-type galaxies. At z = 2 all simulated galaxies with M* ≳ 1011 M☉ (11 out of 40) at z = 2 are compact with projected half-mass radii of ≈0.77 (±0.24) kpc and line-of-sight velocity dispersions within the projected half-mass radius of ≈262 (±28) km s−1 (3 out of 11 are already quiescent). Similar to observed compact early-type galaxies at high redshift, the simulated galaxies are clearly offset from the local mass–size and mass–velocity dispersion relations. Toward redshift zero the sizes increase by a factor of ∼5–6, following R1/2∝(1 + z)α with α = −1.44 for quiescent galaxies (α = −1.12 for all galaxies). The velocity dispersions drop by about one-third since z ≈ 2, following σ1/2∝(1 + z)β with β = 0.44 for the quiescent galaxies (β = 0.37 for all galaxies). The simulated size and dispersion evolution is in good agreement with observations and results from the subsequent accretion and merging of stellar systems at z ≲ 2, which is a natural consequence of the hierarchical structure formation. A significant number of the simulated massive galaxies (7 out of 40) experience no merger more massive than 1:4 (usually considered as major mergers). On average, the dominant accretion mode is stellar minor mergers with a mass-weighted mass ratio of 1:5. We therefore conclude that the evolution of massive early-type galaxies since z ≈ 2 and their present-day properties are predominantly determined by frequent “minor” mergers of moderate mass ratios and not by major mergers alone.