We present deep Hubble Space Telescope Wide Field Camera 3 slitless spectroscopic observations of the distant cluster Cl J1449+0856. These cover a single pointing with 18 orbits of G141 spectroscopy and F140W imaging, allowing us to derive secure redshifts down to m_140~25.5 AB and 3sigma line fluxes of 5*10^(-18) erg/s/cm^2. In particular, we were able to spectroscopically confirm 12 early-type galaxies in the field up to z~3, 6 of which in the cluster core, which represents the first direct spectroscopic confirmation of passive galaxies in a z=2 cluster environment. With 140 redshifts in a ~6 arcmin^2 field, we can trace the spatial and redshift galaxy distribution in the cluster core and background field. We find two strong peaks at z=2.00 and z=2.07, where only one was seen in our previously published ground-based data. Thanks to the spectroscopic confirmation of the cluster ETGs, we can now re-evaluate the redshift of Cl J1449+0856 at z=2.00, rather than z=2.07, with the background overdensity being revealed to be sparse and "sheet"-like. This presents an interesting case of chance alignment of two close yet unrelated structures, each one preferentially selected by different observing strategies. With 6 quiescent or early-type spectroscopic members and 20 star-forming ones, Cl J1449+0856 is now reliably confirmed to be at z=2.00. The identified members can now allow for a detailed study of galaxy properties in the densest environment at z=2.
Spectroscopic Confirmation of the Rich z=1.80 Galaxy Cluster JKCS 041 Using the WFC3 Grism: Environmental Trends in the Ages and Structure of Quiescent Galaxies
How dead are dead galaxies? Mid-Infrared fluxes of quiescent galaxies at redshift 0.3 < z < 2.5: implications for star formation rates and dust heating
The stellar velocity dispersion of a compact massive galaxy at z=1.80 using X-Shooter: confirmation of the evolution in the mass-size and mass-dispersion relations
最近的光度学研究表明，恒星质量固定的早型星系在早期更小，密度更大。在本文中，我们评估发现，推导出这样一个紧凑的静态星系在z=1.8的动力学质量。我们使用VLT上的X-Shooter获得了NMBS-C7447星系全UV-NIR波长覆盖的高质量光谱。我们确定的速度色散为294 +- 51公里/秒。考虑到这种速度色散和1.64 +- 0.15 kpc的有效半径（由HST-WFC 3 F160 W的观测结果确定），我们得出动力学质量为1.7 +- 0.5 x 10^11 Msun。全光谱与恒星星族合成模型的比较表明，NMBS-C774有一个相对年轻的恒星星族（0.40 Gyr），几乎没有恒星形成，恒星质量约为1.5 x 10^11 Msun。动力学和光度恒星质量是很好的协议。因此，我们的研究支持了这样的结论，即静止星系的质量密度在早期确实较高，而这一早期结果不是由系统测量误差引起的。通过结合不同红移下的光谱测量，我们发现在固定动力学质量下，z=1.8时的速度色散比z=0时高出约1.8倍。最后，我们表明，在z>1.5的几个可用的速度色散测量值之间的明显差异是一致的质量-尺寸关系的内在散射。
The FourStar Galaxy Evolution Survey (ZFOURGE): ultraviolet to far-infrared catalogs, medium-bandwidth photometric redshifts with improved accuracy, stellar masses, and confirmation of quiescent galaxies to z~3.5
