Direct Proof for the Formation of Proto-Elliptical Galaxies and Their Origin

我们开发了一种有效的方法来筛选高红移的候选恒星形成椭圆星系，并利用Subaru/ prime- camera成功地发现了许多候选星系（1.4<z<2.5的sBzK和pBzK星系）。sBzK星系目前正处于激烈的恒星形成活动中，它们的恒星质量、空间密度和群集特性与附近的大质量椭圆星系相当。pBzK星系是星暴后星系，恒星质量与sbzk相当，它们的星团和空间密度与本地宇宙星系团中的巨椭圆一样大。这些结果表明BzK星系在其主要形成时期是椭圆星系；sBzKs演化为pBzKs，然后在z~1演化为EROs，最后在z~ 0演化为被动椭圆星系。为了证实sBzK星系SED推断出的高SFRs，我们测量了2个sBzK的1.2mm通量，发现每年的SFRs非常高，为500~1500太阳质量，支持了我们之前关于sBzK星系活跃恒星形成性质的更多发现。这些星系在k波段比在z~2波段的Scuba源更亮，从中我们可以了解到sBzKs有一个非常活跃的恒星形成和密集尘星云的短周期演化阶段。我们还利用近红外三维光谱仪SINFONI在VLT上观测到了一个sBzK星系BzK-15504，这是首次对高红移星系进行这种观测。令人惊讶的是，这个星系有一个快速旋转的圆盘，其质量和旋转速度与银河系的圆盘相当，现在正处于凸起形成阶段，大量气体流入中心的大质量黑洞。目前还不清楚这个巨大的气体盘是否稳定，或者这个星系最终会与其他星系合并形成一个单一的大质量椭圆星系。本研究强烈地提出了大质量椭圆星系形成和演化的以下情景：大质量椭圆星系的形成发生在z~2宇宙，在此之前，质量组装尚未完成，星系的SFRs相对较小（由于缺乏足够的可用气体）。一旦在z~2形成，星系被探测到为sBzK星系，然后演化为pBzK星系，ERO星系，最后是哈勃序列上的巨型椭圆星系。这一过程的时间尺度取决于星系环境，因为星系在密度大的环境中进化得更快，质量大的星系进化得更快。因此，我们发现的z~2大质量椭圆的形成时代应该与一般场相对应，而在星团环境中形成时代可能要早得多。因此，有可能在更高的红移中发现形成恒星的尘埃星系群集。识别这样的原始星系团将会告诉我们很多关于椭圆星系婴儿期的信息。少

We have developed an effective way to cull the candidates for star forming elliptical galaxies at high redshift, and have successfully discovered numerous candidates (sBzK and pBzK galaxies at 1.4<z<2.5) by using the Subaru/Suprime-Camera. sBzK galaxies are currently under intense star forming activity, and their stellar masses, spatial densities, and clustering properties are comparable to those of nearby massive ellipticals. pBzK galaxies are post starburst galaxies with comparable stellar masses to sBzKs and their clustering and spatial densities are as large as giant ellipticals in clusters of galaxies of the local universe. These results suggest that BzK galaxies are elliptical galaxies in their major formation epoch; sBzKs evolve to pBzKs, then to EROs at z~1, and finally to passive elliptical galaxies at z-0. To confirm high SFRs inferred from SED of sBzK galaxies, we measured 1.2mm flux of 2 sBzKs to find very high SFRs as 500~1500 solar mass per year, supporting our previous f … More indings of active star forming nature of sBzK galaxies. These galaxies are more luminous in K-band than Scuba sources at z~2, from which one can learn that sBzKs had a short-period evolutionary stage of very active star formation with dense dust clouds. We have also observed one sBzK galaxy, BzK-15504 with near infrared 3D spectrograph SINFONI on VLT for the first time of this kind of observation of high redshift galaxies. Surprisingly, this galaxy has a rapidly rotating disk of comparable mass and rotational velocity to those of the Milky Way disk, and is now in the stage of bulge formation with gas infall of considerable amount into a central massive black hole. It is not clear is if this massive gas disk is stable, or the galaxy will eventually merge with other galaxies to form a single massive elliptical galaxy.This study strongly suggests the following scenario for the formation and evolution of massive elliptical galaxies: The formation of massive ellipticals occur at z~2 universe, before which mass assembly has not yet completed and galaxies have relatively smaller SFRs (due to a lack of sufficient gas available). Once formed at z~2, galaxies are detected as sBzK galaxies, which then evolve into pBzK galaxies, ERO galaxies, and finally giant elliptical galaxies on the Hubble sequence. The timescale of this process would depend on the galaxy environment in the sense that galaxies evolve much quicker in dense environment and more massive galaxies evolve more rapidly. Thus, our finding of the formation epoch of massive ellipticals at z~2 should correspond to the general field and the formation epoch could be much earlier in the cluster environments. Thus there is a possibility to discover clustering of star forming dusty galaxies at much higher redshift. Identifying such proto-clusters of galaxies would tell a lot about elliptical galaxies in their infant ages. Less