We use 1221 galaxies with unusually high gas-phase metallicity to study their physical properties.The scope of redshift is 0.02 < z < 0.25 for these galaxies with unusually high gas-phase metallicity.Our goal is...We use 1221 galaxies with unusually high gas-phase metallicity to study their physical properties.The scope of redshift is 0.02 < z < 0.25 for these galaxies with unusually high gas-phase metallicity.Our goal is to understand the physical origins of the high gas-phase metallicity.To address this study,we select a control sample matching similar redshift and stellar mass.Our main results are as follows.(i) Compared with the control sample,the high-metallicity sample shows lower ionization parameter,higher electron density and more dust content.(ii) We also find that the high-metallicity sample has older stellar age and higher [Mgb/] ratio,which indicates that the high-metallicity sample has shorter timescale of star formation.(iii) According to the plane of Hδ_A vs.D_n4000,we can see that the control sample has higher HδAand lower D_n4000 than the high-metallicity sample,which may imply that the control sample experiences recent star formation.(iv) There is a significant difference in gas distribution between the highmetallicity and control samples.The high-metallicity sample has lower gas fraction than control sample,which indicates that galaxies have high gas-phase metallicity probably due to their low HI gas fraction.(v) There is no significant difference between the high-metallicity and control samples in environment,which may suggest that the environment has no effect on gas-phase metallicity.展开更多
The number density and clustering properties of Lyman break galaxies (LBGs) observed at redshift z～3 are best explained by assuming that they are associated with the most massive haloes at z～3 predicted in hierarchi...The number density and clustering properties of Lyman break galaxies (LBGs) observed at redshift z～3 are best explained by assuming that they are associated with the most massive haloes at z～3 predicted in hierarchical models of structure formation. In this paper we study, under the same assumption, how star formation and chemical enrichment may have proceeded in the LBG population. We find that gas cooling in dark haloes provides a natural regulation process. The predicted star formation rates and effective radii are consistent with observations. Still, the predicted metallicity distribution, the contribution to the total metals and the contributions to the soft X ray background and to the UV ionization background of LBGs are presented and the discussions are given.展开更多
We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is ...We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is limited to a narrow range in the color-stellar mass diagram. After splitting green valley galaxies into two parts—a bluer green valley(green 1) and a redder one(green 2) and three stellar mass bins,we investigate the variation of physical properties across the green valley region. Our main results are as follows:(i) The percentages of pure bulge and bulge-dominated/elliptical galaxies increase gradually from blue cloud to red sequence while the percentages of pure disk and disk-dominated/spiral galaxies decrease gradually in all stellar mass bins and different environments.(ii) With the analysis of morphological and structural parameters(e.g., concentration(C) and the stellar mass surface density within the central 1 kpc(Σ1)), red galaxies show more luminous and compact cores than both green valley and blue galaxies, while blue galaxies show the opposite behavior in all stellar mass bins.(iii) A strong negative(positive) relationship between bulge-to-total light ratio(B/T) and specific star formation rate(sSFR)(D_(4000)) is found from blue to red galaxies. Our results indicate that the growth in bulge plays an important role when the galaxies change from the blue cloud, to the green valley and to the red sequence.展开更多
We compile multi-wavelength data from ultraviolet to infrared(IR) bands as well as redshift and source-type information, for a large sample of 178 341 sources in the Hawaii-Hubble Deep Field-North field. A total of 14...We compile multi-wavelength data from ultraviolet to infrared(IR) bands as well as redshift and source-type information, for a large sample of 178 341 sources in the Hawaii-Hubble Deep Field-North field. A total of 145 635 sources among the full sample are classified/treated as galaxies and have redshift information available. We derive physical properties for these sources utilizing the spectral energy distribution fitting code CIGALE that is based on Bayesian analysis. Through various consistency and robustness checks, we find that our stellar-mass and star-formation rate(SFR) estimates are reliable, which is mainly due to two facts. Firstly, we adopt the most up-to-date and accurate redshifts and point spread functionmatched photometry; and secondly, we make sensible parameter choices with the CIGALE code and take into account the influences of mid-IR/far-IR data, star-formation history models, and AGN contribution. We release our catalog of galaxy properties publicly(including, e.g., redshift, stellar mass, SFR, age, metallicity, dust attenuation). It is the largest of its kind in this field and should facilitate future relevant studies on the formation and evolution of galaxies.展开更多
利用赫歇尔空间望远镜的H-ATLAS(Herschel Astrophysical Terahertz Large Area Survey)SDP(Science Demonstration Phase)天区从紫外到亚毫米波段数据,结合星族合成方法和尘埃模型,计算了星系的红外总光度.在此基础上,分别针对强恒星...利用赫歇尔空间望远镜的H-ATLAS(Herschel Astrophysical Terahertz Large Area Survey)SDP(Science Demonstration Phase)天区从紫外到亚毫米波段数据,结合星族合成方法和尘埃模型,计算了星系的红外总光度.在此基础上,分别针对强恒星形成星系和弱恒星形成星系,研究了利用紫外光度、红外光度和Hα谱线计算得到的恒星形成率(Star Formation Rate,SFR)的差异以及导致差异的内在物理起因.发现对于恒星形成活动强的星系,这3种恒星形成率指针给出的结果基本一致,弥散较小、只是在高恒星形成率端,利用紫外光度算得的恒星形成率比利用Hα谱线流量算得的恒星形成率略微偏小;而在低恒星形成率端,紫外光度指针偏大于Hα谱线指针;红外光度指针与Hα谱线指针在两端无明显偏差.对弱恒星形成星系,紫外光度、Hα谱线和红外光度3种恒星形成率指针存在明显的差异,且弥散较大.利用紫外光度和Hα谱线计算得到的恒星形成率的弥散和系统偏差随着星系年龄、质量的增加而增大.系统偏差增大的主要原因是利用紫外连续谱斜率β定标恒星形成活动较弱星系的消光时,高估了这些星系的紫外消光,使得消光改正后的紫外光度偏大.另外,MPA/JHU(Max Planck Institute for Astrophysics/Johns Hopkins University)数据库中弱恒星形成星系的恒星形成率SFR(Hα)比真实值偏低.展开更多
Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects ...Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects for future advances.展开更多
Stellar bars are important for the secular evolution of disk galaxies because they can drive gas into the galactic central regions. To investigate the star formation properties in barred galaxies, we presented a multi...Stellar bars are important for the secular evolution of disk galaxies because they can drive gas into the galactic central regions. To investigate the star formation properties in barred galaxies, we presented a multi-wavelength study of two barred galaxies： NGC 2903 and NGC 7080. We performed the three-component bulge-diskbar decomposition using the 3.6 μm images, and identified the bulges in the two galaxies as pseudobulges. Based on the narrowband Hα images, the star formation clumps were identified and analyzed. The clumps in the bulge regions have the highest surface densities of star formation rates in both galaxies, while the star formation activities in the bar of NGC 2903 are more intense than those in the bar of NGC 7080. Finally, we compared our results with the scenario of bar-driven secular evolution in previous studies, and discussed the possible evolutionary stages of the two galaxies.展开更多
Semi-analytic models of galaxy formation are powerful tools to study the evolution of a galaxy population in a cosmological context. However, most models overpredict the number of low- mass galaxies at high redshifts ...Semi-analytic models of galaxy formation are powerful tools to study the evolution of a galaxy population in a cosmological context. However, most models overpredict the number of low- mass galaxies at high redshifts and the colors of model galaxies are not right in the sense that low-mass satellite galaxies are too red and centrals are too blue. The recent version of the L-Galaxies model by Henriques et al. （H15） is a step forward to solve these problems by reproducing the evolution of stellar mass function and the overall fraction of red galaxies. In this paper we compare the two model predictions of L-Galaxies （the other is Guo et al., G13） to SDSS data in detail. We find that in the H15 model the red fraction of central galaxies now agrees with the data due to their implementation of strong AGN feedback, but the stellar mass of centrals in massive halos is now slightly lower than what is indicated by the data. For satellite galaxies, the red fraction of low-mass galaxies （log M./M~ 〈 10） also agrees with the data, but the color of massive satellites （10 〈 logM,/M~ 〈 11） is slightly bluer. The correct color of centrals and the bluer color of massive satellites indicate that quenching in massive satellites is not strong enough. We also find that there are too many red spirals and less bulge-dominated galaxies in both H15 and G13 models. Our results suggest that additional mechanisms, such as more minor mergers or disk instability, are needed to slightly increase the stellar mass of the central galaxy in massive galaxies, mainly in the bulge component, and bulge dominated galaxies will be quenched not only by minor mergers, but also by some other mechanisms.展开更多
We report the discovery of an isolated compact galaxy triplet SDSS J084843.45＋164417.3, which is first detected by the LAMOST spectral survey and then confirmed by a spectroscopic observation of the BFOSC mounted on ...We report the discovery of an isolated compact galaxy triplet SDSS J084843.45＋164417.3, which is first detected by the LAMOST spectral survey and then confirmed by a spectroscopic observation of the BFOSC mounted on the 2.16 meter telescope located at Xinglong Station, which is administered by National Astronomical Observatories, Chinese Academy of Sciences. It is found that this triplet is an iso- lated and extremely compact system, which has an aligned configuration and very small radial velocity dispersion. The member galaxies have similar colors and show marginal star formation activities. These results support the opinion that the compact triplets are well-evolved systems rather than hierarchically forming structures. This serendipitous discovery reveals the limitations of fiber spectral redshift surveys in studying such a compact system, and demonstrates the necessity of additional observations to complete the current redshift sample.展开更多
We re-examine the properties of the star cluster population in the circumnuclear starburst ring in the face-on spiral galaxy NGC 7742, whose young cluster mass function has been reported to exhibit significant deviati...We re-examine the properties of the star cluster population in the circumnuclear starburst ring in the face-on spiral galaxy NGC 7742, whose young cluster mass function has been reported to exhibit significant deviations from the canonical power law. We base our reassessment on the clusters＇ luminosi- ties （an observational quantity） rather than their masses （a derived quantity）, and confirm conclusively that the galaxy＇s starburst-ring clusters--and particularly the youngest subsample, log（t yr-1） ≤7.2- show evidence of a turnover in the cluster luminosity function well above the 90% completeness limit adopted to ensure the reliability of our results. This confirmation emphasizes the unique conundrum posed by this unusual cluster population.展开更多
Stellar populations contain the most important information about star cluster formation and evo- lution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar po...Stellar populations contain the most important information about star cluster formation and evo- lution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations （SSPs）. However, discoveries of multiple stellar populations in Galactic globular clus- ters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar popu- lations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including ob- servational results and scenarios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.展开更多
从观测上测定早型星系中恒星形成活动随红移的演化有助于理解这类星系的形成演化.结合GEMS(Galaxy Evolution from Morphology and SEDs)巡天的HST/ACS(Hubble Space Telescope/Advanced Camera for Surveys)高分辨图像和CDFS(ChandraDe...从观测上测定早型星系中恒星形成活动随红移的演化有助于理解这类星系的形成演化.结合GEMS(Galaxy Evolution from Morphology and SEDs)巡天的HST/ACS(Hubble Space Telescope/Advanced Camera for Surveys)高分辨图像和CDFS(ChandraDeep Field South)天区Spitzer、GALEX(Galaxy Evolution Explorer)等多波段数据,基于形态、颜色和恒星质量选出一个0.2≤z≤1.0红移范围的包含456个早型星系的完备样本.利用stacking技术测量了样本星系紫外与红外平均光度,估计早型星系的恒星形成率.结果显示,早型星系中的恒星形成率较低(<3 M_⊙·yr^(-1)),随红移递减而降低.在红移z=1以来的恒星形成贡献的质量小于15%.星族分析亦肯定大质量早型星系的主体星族形成于宇宙早期(z>2).展开更多
基金supported by the National Key Research and Development Program of China(No.2017YFA0402703)the National Natural Science Foundation of China(Grant Nos.11733002and 11773013)
文摘We use 1221 galaxies with unusually high gas-phase metallicity to study their physical properties.The scope of redshift is 0.02 < z < 0.25 for these galaxies with unusually high gas-phase metallicity.Our goal is to understand the physical origins of the high gas-phase metallicity.To address this study,we select a control sample matching similar redshift and stellar mass.Our main results are as follows.(i) Compared with the control sample,the high-metallicity sample shows lower ionization parameter,higher electron density and more dust content.(ii) We also find that the high-metallicity sample has older stellar age and higher [Mgb/] ratio,which indicates that the high-metallicity sample has shorter timescale of star formation.(iii) According to the plane of Hδ_A vs.D_n4000,we can see that the control sample has higher HδAand lower D_n4000 than the high-metallicity sample,which may imply that the control sample experiences recent star formation.(iv) There is a significant difference in gas distribution between the highmetallicity and control samples.The high-metallicity sample has lower gas fraction than control sample,which indicates that galaxies have high gas-phase metallicity probably due to their low HI gas fraction.(v) There is no significant difference between the high-metallicity and control samples in environment,which may suggest that the environment has no effect on gas-phase metallicity.
文摘The number density and clustering properties of Lyman break galaxies (LBGs) observed at redshift z～3 are best explained by assuming that they are associated with the most massive haloes at z～3 predicted in hierarchical models of structure formation. In this paper we study, under the same assumption, how star formation and chemical enrichment may have proceeded in the LBG population. We find that gas cooling in dark haloes provides a natural regulation process. The predicted star formation rates and effective radii are consistent with observations. Still, the predicted metallicity distribution, the contribution to the total metals and the contributions to the soft X ray background and to the UV ionization background of LBGs are presented and the discussions are given.
基金supported by the National Key Research and Development Program of China (No. 2017YFA0402703)by the National Natural Science Foundation of China (No. 11733002)
文摘We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is limited to a narrow range in the color-stellar mass diagram. After splitting green valley galaxies into two parts—a bluer green valley(green 1) and a redder one(green 2) and three stellar mass bins,we investigate the variation of physical properties across the green valley region. Our main results are as follows:(i) The percentages of pure bulge and bulge-dominated/elliptical galaxies increase gradually from blue cloud to red sequence while the percentages of pure disk and disk-dominated/spiral galaxies decrease gradually in all stellar mass bins and different environments.(ii) With the analysis of morphological and structural parameters(e.g., concentration(C) and the stellar mass surface density within the central 1 kpc(Σ1)), red galaxies show more luminous and compact cores than both green valley and blue galaxies, while blue galaxies show the opposite behavior in all stellar mass bins.(iii) A strong negative(positive) relationship between bulge-to-total light ratio(B/T) and specific star formation rate(sSFR)(D_(4000)) is found from blue to red galaxies. Our results indicate that the growth in bulge plays an important role when the galaxies change from the blue cloud, to the green valley and to the red sequence.
基金support from the 973 Program (2015CB857004)the National Natural Science Foundation of China (GrantNos. 11890693, 11473026 and 11421303)the CAS Frontier Science Key Research Program (QYZDJ-SSW-SLH006)
文摘We compile multi-wavelength data from ultraviolet to infrared(IR) bands as well as redshift and source-type information, for a large sample of 178 341 sources in the Hawaii-Hubble Deep Field-North field. A total of 145 635 sources among the full sample are classified/treated as galaxies and have redshift information available. We derive physical properties for these sources utilizing the spectral energy distribution fitting code CIGALE that is based on Bayesian analysis. Through various consistency and robustness checks, we find that our stellar-mass and star-formation rate(SFR) estimates are reliable, which is mainly due to two facts. Firstly, we adopt the most up-to-date and accurate redshifts and point spread functionmatched photometry; and secondly, we make sensible parameter choices with the CIGALE code and take into account the influences of mid-IR/far-IR data, star-formation history models, and AGN contribution. We release our catalog of galaxy properties publicly(including, e.g., redshift, stellar mass, SFR, age, metallicity, dust attenuation). It is the largest of its kind in this field and should facilitate future relevant studies on the formation and evolution of galaxies.
文摘利用赫歇尔空间望远镜的H-ATLAS(Herschel Astrophysical Terahertz Large Area Survey)SDP(Science Demonstration Phase)天区从紫外到亚毫米波段数据,结合星族合成方法和尘埃模型,计算了星系的红外总光度.在此基础上,分别针对强恒星形成星系和弱恒星形成星系,研究了利用紫外光度、红外光度和Hα谱线计算得到的恒星形成率(Star Formation Rate,SFR)的差异以及导致差异的内在物理起因.发现对于恒星形成活动强的星系,这3种恒星形成率指针给出的结果基本一致,弥散较小、只是在高恒星形成率端,利用紫外光度算得的恒星形成率比利用Hα谱线流量算得的恒星形成率略微偏小;而在低恒星形成率端,紫外光度指针偏大于Hα谱线指针;红外光度指针与Hα谱线指针在两端无明显偏差.对弱恒星形成星系,紫外光度、Hα谱线和红外光度3种恒星形成率指针存在明显的差异,且弥散较大.利用紫外光度和Hα谱线计算得到的恒星形成率的弥散和系统偏差随着星系年龄、质量的增加而增大.系统偏差增大的主要原因是利用紫外连续谱斜率β定标恒星形成活动较弱星系的消光时,高估了这些星系的紫外消光,使得消光改正后的紫外光度偏大.另外,MPA/JHU(Max Planck Institute for Astrophysics/Johns Hopkins University)数据库中弱恒星形成星系的恒星形成率SFR(Hα)比真实值偏低.
文摘Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects for future advances.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11173030, 10833006, 10773014,10978014 and 11078017)the National Basic Research Program of China (973 Program,Grant Nos. 2007CB815406 and 2012CB821803)partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy, National Astronomical Observatories,Chinese Academy of Sciences
文摘Stellar bars are important for the secular evolution of disk galaxies because they can drive gas into the galactic central regions. To investigate the star formation properties in barred galaxies, we presented a multi-wavelength study of two barred galaxies： NGC 2903 and NGC 7080. We performed the three-component bulge-diskbar decomposition using the 3.6 μm images, and identified the bulges in the two galaxies as pseudobulges. Based on the narrowband Hα images, the star formation clumps were identified and analyzed. The clumps in the bulge regions have the highest surface densities of star formation rates in both galaxies, while the star formation activities in the bar of NGC 2903 are more intense than those in the bar of NGC 7080. Finally, we compared our results with the scenario of bar-driven secular evolution in previous studies, and discussed the possible evolutionary stages of the two galaxies.
基金supported by the National Basic Research Program of China (2015CB857003 and 2013CB834900)the Natural Science Foundation of Jiangsu Province (No. BK 20140050)+1 种基金the National Natural Science Foundation of China (NSFC, No.11333008)the Strategic Priority Research Program ‘The Emergence of Cosmological Structure’ of CAS (No. XDB09010403)
文摘Semi-analytic models of galaxy formation are powerful tools to study the evolution of a galaxy population in a cosmological context. However, most models overpredict the number of low- mass galaxies at high redshifts and the colors of model galaxies are not right in the sense that low-mass satellite galaxies are too red and centrals are too blue. The recent version of the L-Galaxies model by Henriques et al. （H15） is a step forward to solve these problems by reproducing the evolution of stellar mass function and the overall fraction of red galaxies. In this paper we compare the two model predictions of L-Galaxies （the other is Guo et al., G13） to SDSS data in detail. We find that in the H15 model the red fraction of central galaxies now agrees with the data due to their implementation of strong AGN feedback, but the stellar mass of centrals in massive halos is now slightly lower than what is indicated by the data. For satellite galaxies, the red fraction of low-mass galaxies （log M./M~ 〈 10） also agrees with the data, but the color of massive satellites （10 〈 logM,/M~ 〈 11） is slightly bluer. The correct color of centrals and the bluer color of massive satellites indicate that quenching in massive satellites is not strong enough. We also find that there are too many red spirals and less bulge-dominated galaxies in both H15 and G13 models. Our results suggest that additional mechanisms, such as more minor mergers or disk instability, are needed to slightly increase the stellar mass of the central galaxy in massive galaxies, mainly in the bulge component, and bulge dominated galaxies will be quenched not only by minor mergers, but also by some other mechanisms.
基金supported by the 973 Program(Grant No.2014CB845705)“Strategic Priority Research Program The Emergence of Cosmological Structures”of the Chinese Academy of Sciences(Grant No.XDB09030200)+10 种基金the National Natural Science Foundation of China(Nos.11390373,11573050 and 11433003)supported by the Science Foundation of Shanghai(No.16ZR1442100)Funding for the creation and distribution of the SDSS archive has been provided by the Alfred P.Sloan Foundationthe participating institutions,NASAthe National Science Foundationthe US Department of Energythe Japanese Monbukagakushothe Max Plank SocietyThe Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST,now called the Guo Shou Jing Telescope)is a National Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform CommissionLAMOST is operated and managed by National Astronomical Observatories,Chinese Academy of Sciences
文摘We report the discovery of an isolated compact galaxy triplet SDSS J084843.45＋164417.3, which is first detected by the LAMOST spectral survey and then confirmed by a spectroscopic observation of the BFOSC mounted on the 2.16 meter telescope located at Xinglong Station, which is administered by National Astronomical Observatories, Chinese Academy of Sciences. It is found that this triplet is an iso- lated and extremely compact system, which has an aligned configuration and very small radial velocity dispersion. The member galaxies have similar colors and show marginal star formation activities. These results support the opinion that the compact triplets are well-evolved systems rather than hierarchically forming structures. This serendipitous discovery reveals the limitations of fiber spectral redshift surveys in studying such a compact system, and demonstrates the necessity of additional observations to complete the current redshift sample.
基金supported by the National Key Research and Development Program of China(Grant 2017YFA0402702)the National Natural Science Foundation of China(Grant Nos.U1631102,11373010and 11633005)
文摘We re-examine the properties of the star cluster population in the circumnuclear starburst ring in the face-on spiral galaxy NGC 7742, whose young cluster mass function has been reported to exhibit significant deviations from the canonical power law. We base our reassessment on the clusters＇ luminosi- ties （an observational quantity） rather than their masses （a derived quantity）, and confirm conclusively that the galaxy＇s starburst-ring clusters--and particularly the youngest subsample, log（t yr-1） ≤7.2- show evidence of a turnover in the cluster luminosity function well above the 90% completeness limit adopted to ensure the reliability of our results. This confirmation emphasizes the unique conundrum posed by this unusual cluster population.
基金supported by a Macquarie Research Fellowship and by Strategic Priority Program ‘The Emergence of Cosmological Structures’ of the Chinese Academy of Sciences(Grant XDB09000000)support from the National Natural Science Foundation of China(Grant Nos.11073001,11373010 and 11473037)
文摘Stellar populations contain the most important information about star cluster formation and evo- lution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations （SSPs）. However, discoveries of multiple stellar populations in Galactic globular clus- ters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar popu- lations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including ob- servational results and scenarios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.
文摘从观测上测定早型星系中恒星形成活动随红移的演化有助于理解这类星系的形成演化.结合GEMS(Galaxy Evolution from Morphology and SEDs)巡天的HST/ACS(Hubble Space Telescope/Advanced Camera for Surveys)高分辨图像和CDFS(ChandraDeep Field South)天区Spitzer、GALEX(Galaxy Evolution Explorer)等多波段数据,基于形态、颜色和恒星质量选出一个0.2≤z≤1.0红移范围的包含456个早型星系的完备样本.利用stacking技术测量了样本星系紫外与红外平均光度,估计早型星系的恒星形成率.结果显示,早型星系中的恒星形成率较低(<3 M_⊙·yr^(-1)),随红移递减而降低.在红移z=1以来的恒星形成贡献的质量小于15%.星族分析亦肯定大质量早型星系的主体星族形成于宇宙早期(z>2).
