Several recent studies have shown that about half of the massive galaxies at z~2 are in a quiescent phase. Moreover, these galaxies are commonly found to be ultra-compact with half-light radii of ~1 kpc. We have obtained a ~29 hr spectrum of a typical quiescent, ultra-dense galaxy at z=2.1865 with the Gemini Near-Infrared Spectrograph. The spectrum exhibits a strong optical break and several absorption features, which have not previously been detected in z>2 quiescent galaxies. Comparison of the spectral energy distribution with stellar population synthesis models implies a low star formation rate (SFR) of 1-3 Msol/yr, an age of 1.3-2.2 Gyr, and a stellar mass of ~2x10^11 Msol. We detect several faint emission lines, with emission-line ratios of [NII]/Halpha, [SII]/Halpha and [OII]/[OIII] typical of low-ionization nuclear emission-line regions. Thus, neither the stellar continuum nor the nebular emission implies active star formation. The current SFR is <1% of the past average SFR. If this galaxy is representative of compact quiescent galaxies beyond z=2, it implies that quenching of star formation is extremely efficient and also indicates that low luminosity active galactic nuclei (AGNs) could be common in these objects. Nuclear emission is a potential concern for the size measurement. However, we show that the AGN contributes <8% to the rest-frame optical emission. A possible post-starburst population may affect size measurements more strongly; although a 0.5 Gyr old stellar population can make up <10% of the total stellar mass, it could account for up to ~40% of the optical light. Nevertheless, this spectrum shows that this compact galaxy is dominated by an evolved stellar population.
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
A Strongly-Lensed Massive Ultra-Compact Quiescent Galaxy at z ~ 2.4 in the COSMOS/UltraVISTA Field
We report the discovery of a massive ultra-compact quiescent galaxy that has been strongly-lensed into multiple images by a foreground galaxy at z = 0.960. This system was serendipitously discovered as a set of extremely Ks-bright high-redshift galaxies with red J - Ks colors using new data from the UltraVISTA YJHKs near-infrared survey. The system was also previously identified as an optically-faint lens/source system using the COSMOS ACS imaging by Faure et al. (2008, 2011). Photometric redshifts for the three brightest images of the source galaxy determined from twenty-seven band photometry…
The Evolution of the Stellar Mass Functions of Star-Forming and Quiescent Galaxies to z = 4 from the COSMOS/UltraVISTA Survey
我们目前的恒星质量函数（SMF）的恒星形成和静止星系z = 4使用的样本中的95 675个星系的COSMOS/UltraVISTA字段的测量。从DR 1 UltraVISTA K_{s}波段成像中选择了源，该波段成像覆盖了宽区域（1.62 deg^2）到显著深度（K_{s,tot} = 23.4）的独特组合。合并后的星族的SMF与先前的测量结果非常一致，表明宇宙的恒星质量密度在z = 0.75、2.0和3.5时分别只有当前值的50%、10%和1%。静止的星族驱动了大部分的整体增长，这些星系的恒星质量密度从z = 3.5开始增加了2.71^{+0.93}_{-0.22} dex。在z > 2.5时，恒星形成星系在所有恒星质量的总SMF中占主导地位，尽管静止星系的非零种群持续到z = 4。K_{s}选择的恒星形成星系SMF与紫外选择的SMF在2.5 < z 3.5的比较< 4 show reasonable agreement and suggests UV-selected samples are representative of the majority of the stellar mass density at z >。我们估计的平均质量增长的个别星系选择星系在固定的累积数密度。在z = 0.3时Log（M_{*} / M_{sun}）= 11.5的星系，平均质量自z …
Mass assembly in quiescent and star-forming galaxies since z=4 from UltraVISTA
我们估计了0.2<z<4的恒星形成星系和静止星系的星系质量函数和恒星质量密度。我们构建了一个深K<24的样本220000星系选择使用UltraVISTA DR 1数据发布。我们的分析是基于精确的30波段光度红移。通过将这些测光红移与来自zCOSMOS亮巡天和暗巡天的10800个光谱红移进行比较，我们发现在i<22.5时，sigma（dz/（1+z））=0.008，在1.5<z 10^10.7 Msun时，sigma（dz/（1+zs））=0.03<4. We derive the stellar mass function and correct for the Eddington bias. We find a mass-dependent evolution of the global and star-forming populations. This mass-dependent evolution is a direct consequence of the star formation being quenched in galaxies more massive than M>。对于静止星系的质量函数，我们没有发现z<1的高质量端有任何显著的演化;但是我们观察到暗端斜率明显变平。从z~3到z~1，静止星系的密度在整个质量范围内增加。它们的同向恒星质量…
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
