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Fast jet proper motion discovered in a blazar at z=4.72

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Science Bulletin 2020年第7期65卷 525-530,M0003页

作者： Yingkang Zhang Tao An Sándor Frey Shanghai Astronomical Observatory Chinese Academy of SciencesShanghai 200030China University of Chinese Academy of Sciences Beijing 100049China Key Laboratory of Radio Astronomy Chinese Academy of SciencesNanjing 210008China Konkoly Observatory Research Centre for Astronomy and Earth SciencesKonkoly Thege Miklósút 15-17H-1121 BudapestHungary

high-resolution observations of high-redshift(z > 4) radio quasars offer a unique insight into jet kinematics at early cosmological epochs, as well as constraints on cosmological model *** to the general weakness of extremely distant objects and the apparently slow structural changes caused by cosmological time dilation, only a couple of high-redshift quasars(HRQs) have been studied with parsec-scale resolutions, and with limited number of observing epochs. Here we report on very long baseline interferometry(VLBI) observations of a high-redshift blazar J1430 + 4204(z=4.72) in the 8 GHz frequency band at five different epochs spanning 22 years. The source shows a compact core–jet structure with two jet components being identified within 3 milli-arcsecond(mas) scale. The long time span and multiple-epoch data allow for the kinematic studies of the jet components. That results in a jet proper motion of μ(J1) = 0.017 ± 0.002 mas a^-1 and μ(J2) = 0.156 ± 0.015 mas a^-1, respectively. For the fastest-moving outer jet component J2, the corresponding apparent transverse speed is (19.5 ± 1.9) *** inferred bulk jet Lorentz factor C=14.6 ± 3.8 and viewing angle θ=2.2°± 1.6°indicate highly relativistic beaming. The Lorentz factor and apparent proper motion are the highest measured to date among the z > 4 jetted radio sources, while the jet kinematics is still consistent with the cosmological interpretation of quasar redshifts.

关键词： Nuclei high-redshift Radio continuum Quasars Individual J1430+4204

Stellar Mass Function of Lyman Break Galaxies： Theoretical Perspective

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Chinese Physics Letters 2006年第4期23卷 1061-1064页

作者：刘晓亮黄永清刘念华赖珍荃束成钢 Department of Physics School of Sciences Nanchang University Jiangxi 330047 Joint Center for Astrophysics Shanghai Normal University Shanghai 200234 Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai 200030

Adopting the observational distributions of star formation rates and half-light radii of Lyman break galaxies （LBGs） in the rest frame UV, we investigate empirically the predicted stellar mass function for LBGs. It is found that a peak exists at mass around 1.5 × 10^10M⊙ for their stellar mass function and there have been significant amount of LBGs with stellar masses higher than 10^11M⊙ at z ～ 3. There should be two families for LBG population observed by the Infrared Array Camera （IRAC）（which is a key instrument in the infrared space telescope Spitzer）, one is red and the other is blue, which are consistent with recent works. Moreover, the predicted comoving correlation lengths for LBGs with different stellar masses, i.e., with different 8 μm magnitudes, are also discussed. The red LBGs should be clustered in space more strongly than the blue LBGs. These predictions can and will be tested by the observations of IRAC, and will provide strong constraints on the current hierarchical galaxy formation model.

关键词： SPITZER-SPACE-TELESCOPE STAR-FORMING GALAXIES high-redshift ULTRAVIOLETLUMINOSITY Z-SIMILAR-TO-3 EVOLUTION HALOES

Morphology and structure of extremely red objects at z ～ 1 in the CANDELS-COSMOS field

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Research in Astronomy and Astrophysics 2015年第6期15卷 811-818页

作者： Guan-Wen Fang Zhong-Yang Ma Yang Chen Xu Kong Institute for Astronomy and History of Science and Technology Dali University Key Laboratory for Research in Galaxies and Cosmology University of Science and Technology of China Chinese Academy of Sciences Center for Astrophysics University of Science and Technology of China SISSA via Bonomea 265 I-34136 Trieste Italy

Using high-resolution HST/Wide Field Camera 3 F125W imaging from the CANDELS-COSMOS field, we report the structural and morphological properties of extremely red objects （EROs） at -z 1. Based on the UVJ color criteria, we sepa- rate EROs into two types： old passive galaxies （OGs） and dusty star-forming galaxies （DGs）. For a given stellar mass, we find that the mean size of OGs （DGs） is smaller by a factor of - 2 （1.5） than that of present-day early-type （late-type） galaxies at a rest-frame optical wavelength. We derive the average effective radii of OGs and DGs, corresponding to 2.09 ± 1.13 kpc and 3.27± 1.14 kpc, respectively. Generally, the DGs are heterogeneous, with mixed features including bulges, disks and irregular structures, with relatively high M20, large size and low G. By contrast, OGs have elliptical-like compact morphologies with lower M20, smaller size and higher G, indicating a more concentrated and symmetric spatial extent of the stellar population distribution in OGs than DGs. These findings imply that OGs and DGs have different evolutionary processes, and that the minor merger scenario is the most likely mechanism for the structural properties of OGs. However, the size evolution of DGs is possibly due to the secular evolution of galaxies.

关键词： galaxies evolution -- galaxies: fundamental parameters -- galaxies structure -- galaxies high-redshift

Effects of redshift on the Classifying Criteria of BL Lacertae Objects

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Chinese Journal of Astronomy and Astrophysics 2007年第3期7卷 345-352页

作者： Li Ma Luo-En Chen Guang-Zhong Xie Ji-Yang Ren Zhao-Hua Xie Shu-Bai Zhou Hui Wu Dong-Cheng Mei Department of Physics Yunnan Normal University Kunming 650092 Department of Physics Yuxi Normal College Yuxi 653100 National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 650011 Department of Physics Yunnan University Kunming 650091

We have collected a sample of 70 BL Lacs （33 radio-selected BL Lacs and 37 X-ray selected BL Lacs） with multi-waveband data for investigating the classifying criteria of BL Lacertae Objects. For each source, we estimate its luminosities in radio, optical and X-ray, the broad-band spectral index from radio to X-ray and the peak frequency of the synchrotron emission, and make a statistical analysis of the data obtained. Our main results are as follows：（1） The broad-band spectral index and the peak frequency have no correlation with the redshift, while they are inversely correlated with each other and they could be regarded as equivalent classifying criteria of BL Lac objects. （2） There are significant effects of the luminosity/redshift relation on the observed luminosity distribution in our sample, hence, if the radio luminosity is to be used as a classifying criterion of BL Lac objects, it should not be regarded as equivalent to the broad-band spectral index or the peak frequency. （3） Our resuits supply a specific piece of evidence for the suggestion that the use of luminosities always introduces a redshift bias to the data and show that the location of the peak frequency is not always linked to the luminosity of any wave band.

关键词： galaxies BL Lacertae objects general-galaxies fundamental parametersgalaxies high-redshift

Morphology and structure of BzK-selected galaxies at z ～ 2 in the CANDELS-COSMOS field

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Research in Astronomy and Astrophysics 2015年第6期15卷 819-827页

Utilizing a BzK-selecfion technique, we obtain 14 550 star-forming galaxies （sBzKs） and 1763 passive galaxies （pBzKs） at z - 2 from the K-selected （KAB 〈 22.5） catalog in the COSMOS/UltraVISTA field. The differential number counts of sBzKs and pBzKs are consistent with the results from the literature. Compared to the observed results, semi-analytic models of galaxy formation and evolution provide too few （many） galaxies at the high （low） mass end. Moreover, we find that the star formation rate and stellar mass of sBzKs follow the relation of the main sequence. Based on HST/Wide Field Camera 3 F160W imaging, we find a wide range of morphological diversities for sBzKs, from diffuse to early-type spiral structures, with relatively high M20, large size and low G, while pBzKs have elliptical-like compact morphologies with lower M20, smaller size and higher G, indicating a more concentrated and symmetric spatial extent of stellar population distribution in pBzKs than sBzKs. Furthermore, the sizes of pBzKs （sBzKs） at z - 2 are on average two to three （one to two） times smaller than those of local early-type （late-type） galaxies with similar stellar mass. Our findings imply that the two classes have different evolution models and mass assembly histories.

关键词： galaxies evolution -- galaxies fundamental parameters -- galaxies structure -- galaxies high-redshift

Searching for the earliest galaxies in the 21cm forest

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Science China(Physics,Mechanics & Astronomy) 2010年第6期53卷 1124-1129页

作者： Andrea FERRARA Francisco S. KITAURA Scuola Normale Superiore Piazza dei Cavalieri 756126 PisaItaly

We use a model developed by Xu,Ferrara,and Chen(Mon Not Roy Astron Soc,submitted) to compute the 21 cm line absorption signatures imprinted by star-forming dwarf galaxies(DGs) and starless minihalos(MHs). The method,based on a statistical comparison of the equivalent width(W ν ) distribution and flux correlation function,allows us to derive a simple selection criteria for candidate DGs at very high(z ≤ 8) redshift. We find that ≈18% of the total number of DGs along a line of sight to a target radio source(GRB or quasar) can be identified by the condition W νhigh-mass tail of the DG distribution at high redshift,and are embedded in large HII regions. The criterion W ν>0.37 kHz instead selects ≈11% of MHs. Selected candidate DGs could later be re-observed in the near-IR by the JWST with high efficiency,thus providing a direct probe of the most likely reionization sources.

关键词： cosmology dwarf galaxies high-redshift galaxies radio absorption lines