DYNAMICAL MASSES OF EARLY-TYPE GALAXIES AT z ~ 2: ARE THEY TRULY SUPERDENSE?
DYNAMICAL MASSES OF EARLY-TYPE GALAXIES AT z ~ 2: ARE THEY TRULY SUPERDENSE?
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z ~ 2 处早期型星系的动态质量：它们真的是超稠密的吗？
DOI：
10.1088/0004-637x/704/1/l34
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
Cappellari M
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作者：
Cappellari M
我们测量了恒星速度色散 σ，并从红移 1.4≲ z≲ 2.0 处的星系质量组装超深光谱巡天 (GMASS) 样本中导出了 9 个大质量 (M≈ 10 11 M☉) 早期型星系 (ETG) 的动力学质量。 σ 基于两个 z≈ 1.4 星系的单独光谱以及七个 1.6< z< 2.0 星系的叠加光谱，在 ESO 甚大望远镜上曝光 202 小时。我们基于 Jeans 方程，考虑了观测到的表面亮度（来自深层 HST/ACS 观测）、点扩散函数和狭缝效应，为物体构建了详细的轴对称动力学模型。我们的动力质量 M Jeans 与维里估计 M vir= 5× R e σ 2/G 的一致性在≲ 30% 以内，尽管后者往往更小。我们的 M Jeans 与之前使用恒星种群模型和 11 波段光度测定得出的 M pop 的吻合度在 2 倍以内。这证实了星系本质上是巨大的。在对年龄非常敏感的静止框架U波段中推断的质光比（M/L）U与过去∼1 Gyr（地层红移z f∼3）的被动演化一致。似乎需要“底光”恒星初始质量函数来确保 M Jeans 和 M pop 在 z∼2 处的紧密一致，就像在 z∼0 处一样。GMASS ETG 平均比其本地对应物更密集。然而，少数具有相似动态质量的局部 ETG 在 Re 内也具有相当的 σ 和质量表面密度 Σ 50 。
We measured stellar velocity dispersions σ and derived dynamical masses of nine massive (M≈ 10 11 M☉) early-type galaxies (ETGs) from the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample at redshift 1.4≲ z≲ 2.0. The σ are based on individual spectra for two galaxies at z≈ 1.4 and on a stacked spectrum for seven galaxies with 1.6< z< 2.0, with 202 hr of exposure at the ESO Very Large Telescope. We constructed detailed axisymmetric dynamical models for the objects, based on the Jeans equations, taking the observed surface brightness (from deep HST/ACS observations), point-spread function, and slit effects into account. Our dynamical masses M Jeans agree within≲ 30% with virial estimates M vir= 5× R e σ 2/G, although the latter tend to be smaller. Our M Jeans also agrees within a factor≲ 2 with the M pop previously derived using stellar population models and 11 bands photometry. This confirms that the galaxies are intrinsically massive. The inferred mass-to-light ratios (M/L) U in the very age-sensitive rest-frame U band are consistent with passive evolution in the past∼ 1 Gyr (formation redshift z f∼ 3). A" bottom-light" stellar initial mass function appears to be required to ensure close agreement between M Jeans and M pop at z∼ 2, as it does at z∼ 0. The GMASS ETGs are on average more dense than their local counterpart. However, a few percent of local ETGs of similar dynamical masses also have comparable σ and mass surface density Σ 50 inside R e.