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{\LARGE\bf Chinese Journal of Astronomy and Astrophysics}\\ }$

2008, Vol.8, No.1 (February 20, 2008)



Extragalactic Astronomy


Galactic Structure and Dynamics

Astrometry and Celestial Mechanics

Instruments, Observational Techniques and Data Processing


Star-Forming Galaxies at $z \sim 2$ in the Hubble Ultra Deep Field

Xu Kong 1,2, Wei Zhang 1,3 and Min Wang 1

1 Center for Astrophysics, University of Science and Technology of China, Hefei 230026; xkong@ustc.edu.cn

2 Joint Institute for Galaxy and Cosmology (JOINGC) of SHAO and USTC 3 National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012

Using a simple color selection based on B-, z- and K-band photometry, $BzK= (z-K)_{\rm AB}-(B-z)_{\rm AB}>-0.2$, we picked out 52 star-forming galaxies at $1.4\lsim z \lsim 2.5$ () from a K-band selected sample ($\Kv<22.0$) in an area of $\sim 5.5$ arcmin2 of the Hubble Ultra Deep Field (UDF). We develop a new photometric redshift method, and the error in our photometric redshifts is less than 0.02(1+z). From the photometric redshift distribution, we find the BzK color criterion can be used to select star-forming galaxies at $1.4\lsim z \lsim 2.5$ with $\Kv<22.0$. Down to $\Kv<22.0$, the number counts of increase linearly with the K magnitude; the are strongly clustered, and most of them have irregular morphologies on the ACS images. They have a median reddening of $E(B-V)\sim0.28$, an average star formation rate of $\sim36\ M_{\odot}$ yr-1 and a typical stellar mass of $\sim10^{10}M_\odot$. The UV criterion for the galaxies at $z \sim 2$ can select most of the faint in the UDF, but it does not work well for bright, massive, highly-reddened, actively star-forming galaxies.

Key Words:   galaxies: evolution --galaxies: high-redshift -- galaxies: photometry -- cosmology: observations
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Growth of Black Holes and Their Host Spheroids in (Sub)mm-loud High-Redshift QSOs

Cai-Na Hao 1,2,3, Xiao-Yang Xia 1, Shu-De Mao 4, Zu-Gan Deng 5 and Hong Wu 2

1 Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300384; hcn@ast.cam.ac.uk

2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

3 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

4 Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire SK11 9DL, UK

5 Graduate School of Chinese Academy of Sciences, Beijing 100049

We study the growth of black holes and stellar population in spheroids at high redshift using several (sub)mm-loud QSO samples. Applying the same criteria established in an earlier work, we find that, similar to IR QSOs at low redshift, the far-infrared emission of these (sub)mm-loud QSOs mainly originates from dust heated by starbursts. By combining low-z IR QSOs and high-z (sub)mm-loud QSOs, we find a trend that the star formation rate ($\Mstardot$) increases with the accretion rate ($\Mdot$). We compare the values of $\Mstardot/\Mdot$ for submm emitting galaxies (SMGs), far-infrared ultraluminous/hyperluminous QSOs and typical QSOs, and construct a likely evolution scenario for these objects. The (sub)mm-loud QSO transition phase has both high $\Mdot$ and $\Mstardot$ and hence is important for establishing the correlation between the masses of black holes and spheroids.

Key Words:   galaxies: active -- galaxies: evolution -- galaxies: high-redshift -- galaxies: interactions -- quasars: general -- galaxies: starburst
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Gaseous versus Stellar Velocity Dispersion in Emission-Line Galaxies

Xiao-Yan Chen 1,2,3, Cai-Na Hao 1,4 and Jing Wang 2

1 Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300384; chenxy@bao.ac.cn

2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

3 Graduate School of Chinese Academy of Sciences, Beijing 100049

4 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

We compare the ionized gas velocity dispersion $\sigma_{\rm gas}$ with the stellar velocity dispersion $\sigma_{\rm\ast}$ in star-forming galaxies, composite galaxies, Low Ionization Nuclear Emission-line Regions (LINERs) and Seyfert 2s, compiled from a cross-identification of Sloan Digital Sky Survey Fourth Data Release (SDSS DR4) and Point Source Catalogue Redshift Survey (PSCz). We measure $\sigma_{\rm gas}$ from the FWHMs of emission lines (H$\alpha$, [NII] $\lambda\lambda$6548, 6583 and [SII] $\lambda\lambda$6716, 6731). A significant correlation between the gas and stellar velocity dispersion exists, despite substantial scatter. The mean value of the gas to stellar velocity dispersion ratio is close to unity. This suggests that gas velocity dispersion can substitute for the stellar velocity dispersion as a tracer of the gravitational potential well for all the four types of galaxies, but the involved uncertainties are different from type to type. We also studied $\overline {\sigma}_{\rm gas}/\sigma_{\rm\ast}$ as a function of the redshift and the axial ratio to test the effects of aperture and galaxy inclination, and found that both effects are weak. Finally we checked the trend of $\overline {\sigma}_{\rm gas}/\sigma_{\rm\ast}$ with the infrared luminosity and found no significant correlation.

Key Words:   galaxies: active -- galaxies: interactions -- galaxies: star-forming -- galaxies: Seyfert
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A New Approach for Estimating Kinetic Luminosity of Jet in AGNs

Mao-Li Ma, Xin-Wu Cao, Dong-Rong Jiang and Min-Feng Gu

Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030; mamaoli@shao.ac.cn

The Königl inhomogeneous jet model can successfully reproduce most observational features of jets in active galactic nuclei (AGN), when suitable physical parameters are adopted. We improve Königl's calculations on the core emission from the jet with a small viewing angle $\theta_0\sim\varphi$ ($\varphi$ is half opening angle of the conical jet). The proper motion of the jet component provides a constraint on the jet kinematics. Based on the inhomogeneous jet model, we use the proper motion data of the jet component to calculate the minimal kinetic luminosity of the jet required to reproduce the core emission measured by the very-long-baseline interferometry (VLBI) for a sample of BL Lac objects. Our results show that the minimal kinetic luminosity is slightly higher than the bolometric luminosity for most sources in the sample, which implies that radiatively inefficient accretion flows (RIAFs) may be in those BL Lac objects, or/and the properties of their broad-line regions (BLRs) are significantly different from flat-spectrum radio-loud quasars.

Key Words:   galaxies: jet -- kinematics and dynamics: theory -- radiation mechanisms: nonthermal-BL Lac objects: general
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Geometry of Broad Line Regions of Active Galactic Nuclei

Xiao-Rong Lü

1 Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049; rrlv2003@yahoo.com.cn

2 Graduate School of Chinese Academy of Sciences, Beijing 100049

It has long remained an open question as to the geometry of the broad line region (BLR) in active galactic nuclei (AGNs). The reverberation mapping technique which measures the response of the broad emission lines to the ionizing continuum, when combined with multiwavelength continuum fitted by sophisticated accretion disks, provides a way of probing the BLR geometry. We analyze a sample of 35 AGNs, which have been monitored by the reverberation mapping campaign. In view of energy budget, the reverberation-based BH masses are found to be in agreement with those obtained by accretion disk models in two thirds of the present sample while the reverberation mapping methods underestimate the BH masses in about one third of objects, as also suggested by Collin et al. in a recent work. We point out that there are obviously two kinds of BLR geometry, which are strongly dependent on the Eddington ratio, and separated by the value $L_{\rm Bol}/L_{\rm Edd}\sim0.1$. These results prefer a scenario of the disk and wind configuration of the BLR and identify the Eddington ratio as the physical driver regulating the wind in the BLR.

Key Words:   accretion, accretion disks -- galaxies: active -- galaxies: Seyfert -- quasars: general
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Model-Synthesized Rate of Type Ia Supernovae and its Influence on the Chemical Enrichment of the ISM

Wen Guo 1,2, Feng-Hui Zhang 1, Xiang-Cun Meng 1,2, Zhong-Mu Li 1,2 and Zhan-Wen Han 1

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; zhanwenhan@ynao.ac.cn

2 Graduate School of Chinese Academy of Sciences, Beijing 100049

Using Hurley's rapid binary stellar evolution code, we have studied the model-synthesized rate of Type Ia Supernovae (SNe Ia) and its influence on the chemical enrichment of the interstellar medium ejected by stellar populations. We adopt two popular scenarios, i.e., single degenerate scenario (SD) and double degenerate scenario (DD), for the progenitors of SNe Ia to calculate the rates of SNe Ia. Rates calculated in this work agree with that of Hachisu et al. and Han $\&$ Podsiadlowski, but are different from that usually adopted in chemical evolution models of galaxies. We apply the rates of SNe Ia to the chemical enrichment (especially Fe enrichment), then compare the results with previous studies. As known SNe Ia slightly affect the enrichment of C, N, O and Mg elements, while significantly affect the enrichment of Fe. We find that the occurrence and the value of the Fe enrichment in our models are earlier and smaller than that commonly adopted in chemical evolution models. We also study the evolution of [Mg/Fe] ratios, which are almost reciprocals of the Fe enrichment. The study may provide constraints on the free parameters of chemical evolution models of galaxies and evolutionary population synthesis.

Key Words:   galaxies: abundances -- supernovae: general--galaxies: stellar content--white dwarfs
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Distribution of 56Ni Yields of Type Ia Supernovae and its Implication for Progenitors

Bo Wang 1,2, Xiang-Cun Meng 1,2, Xiao-Feng Wang 3,4 and Zhan-Wen Han 1

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; wangbo1129@hotmail.com

2 Graduate School of Chinese Academy of Sciences, Beijing 100049

3 Tsinghua Center for Astrophysics (THCA) and Department of Physics, Tsinghua University, Beijing 100084

4 Astronomy Department, University of California at Berkeley, CA 94720, USA

The amount of 56Ni produced in Type Ia supernova (SN Ia) explosion is probably the most important physical parameter underlying the observed correlation of SN Ia luminosities with their light curves. Based on an empirical relation between the 56Ni mass and the light curve parameter $\Delta m_{15}$, we obtained rough estimates of the 56Ni mass for a large sample of nearby SNe Ia with the aim of exploring the diversity in SN Ia. We found that the derived 56Ni masses for different SNe Ia could vary by a factor of ten (e.g., $M_{\rm
Ni}=0.1 - 1.3$$M_{\odot}$), which cannot be explained in terms of the standard Chandrasekhar-mass model (with a 56Ni mass production of 0.4 - 0.8$M_{\odot}$). Different explosion and/or progenitor models are clearly required for various SNe Ia, in particular, for those extremely nickel-poor and nickel-rich producers. The nickel-rich (with $M_{\rm Ni}$ > 0.8$M_{\odot}$) SNe Ia are very luminous and may have massive progenitors exceeding the Chandrasekhar-mass limit since extra progenitor fuel is required to produce more 56Ni to power the light curve. This is also consistent with the finding that the intrinsically bright SNe Ia prefer to occur in stellar environments of young and massive stars. For example, 75$\%$ SNe Ia in spirals have $\Delta m_{15} < 1.2$ while this ratio is only 18$\%$ in E/S0 galaxies. The nickel-poor SNe Ia (with $M_{\rm Ni}$ < 0.2$M_{\odot}$) may invoke the sub-Chandrasekhar model, as most of them were found in early-type E/S0 galaxies dominated by the older and low-mass stellar populations. This indicates that SNe Ia in spiral and E/S0 galaxies have progenitors of different properties.

Key Words:   stars: evolution -- supernovae : general -- white dwarfs
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A Close Correlation between the Spectral Lags and Redshifts of Gamma-Ray Bursts

Ting-Feng Yi 1, Guang-Zhong Xie 2,3 and Fu-Wen Zhang 2,4

1 Physics Department, Yunnan University, Kunming 650091; yitingfeng@ynao.ac.cn

2 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011

3 Yunnan Astronomical Center, Yunnan University, Kunming 650091

4 Graduate School of Chinese Academy of Sciences, Beijing 100049

Based on nine BATSE GRBs with known redshifts, we found that the maximum spectral lag of all the pulses in a gamma-ray burst (GRB) appears to be anti-correlated with the redshift of the burst. In order to confirm this finding, we analyzed 10 GRBs detected by HETE-2 with known redshifts and found a similar relation. Using the relation, we estimated the redshifts of 878 long GRBs in the BATSE catalog, then we investigated the distributions of the redshifts and 869 $E_{\rm iso}$ of these GRBs. The distribution of the estimated redshifts is concentrated at z=1.4 and the distribution of $E_{\rm iso}$ peaks at 1052.5erg. The underlying physics of the correlation is unclear at present.

Key Words:   gamma-rays: bursts -- gamma-rays: observations -- methods: statistical
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Possible Contribution of Mature $\gamma$-ray Pulsars to Cosmic-ray Positrons

Quan-Gui Gao 1, Ze-Jun Jiang 2 and Li Zhang1,2

1 National Astronomical Observatories / Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011

2 Department of Physics, Yunnan University, Kunming 650091; zjjiang@ynu.edu.cn

We restudy the possible contribution of mature gamma-ray pulsars to cosmic ray positrons based on the new version of outer gap model. In this model, the inclination angle and average properties of the outer gap are taken into account, and more mature pulsars can have the outer gap and emit high energy photons. Half of the primary particles in the outer gaps will flow back toward the star surface and emit synchrotron photons, which can produce electron/positron pairs by the cascade of pair production. Some of these pairs will escape from the light cylinder and be accelerated to relativistic energies in the pulsar wind driven by low-frequency electromagnetic waves. Using a Monte Carlo method, we obtain a sample of mature gamma-ray pulsars and then calculate the production of the positrons from these pulsars. The observed excess of cosmic positrons can be well explained by this model.

Key Words:   stars: pulsars: general -- acceleration of particles -- ISM: cosmic rays
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Weak Elliptical Distortion of the Milky Way Potential traced by Open Clusters

Zi Zhu

Department of Astronomy, Nanjing University, Nanjing 210093; zhuzi@nju.edu.cn

From photometric observations and star counts, the existence of a bar in the central few kpc of the Galaxy is suggested. It is generally thought that our Galaxy is surrounded by a massive invisible halo. The gravitational potential of the Galaxy is therefore made non-axisymmetric generated by the central triaxial bar, by the outer triaxial halo, and/or by the spiral structures. Selecting nearly 300 open clusters with complete spatial velocity measurements and ages, we were able to construct the rotation curve of the Milky Way within a range of 3kpc of the Sun. Using a dynamic model for an assumed elliptical disk, a clear weak elliptical potential of the disk with ellipticity of $\epsilon(R_0) = 0.060\pm0.012$ is detected, the Sun is found to be near the minor axis, displaced by $30\dg\pm3\dg$. The motion of the clusters is suggested to be on an oval orbit rather than on a circular one.

Key Words:   Galaxy: disk -- Galaxy: kinematics and dynamics -- Galaxy: open clusters and associations: general -- Galaxy: structure
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A New Critical Value Concerning the Genealogy of Long Period Families at L4 in the Restricted Three-body Problem

Xi-Yun Hou 1,2 and Lin Liu 1,2

1 Astronomy Department, Nanjing University, Nanjing 210093; xiyun.hou@gmail.com

2 Institute of Space Environment and Astronautics, Nanjing University, Nanjing 210093

We found another critical mass ratio value $\overline{\mu}$ between $\mu_4$ and $\mu_5$ concerning the genealogy of the long period family around the equilateral equilibrium point L4 in the restricted three-body problem. This value has not been pointed out before. We used numerical computations to show how the long period family evolves around this critical value. The case is similar to that of the critical values between $\mu_2$ and $\mu_4$, with slight difference in evolution details.

Key Words:   celestial mechanics -- restricted three-body problem -- equilateral equilibrium point -- periodic orbits
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Periodic Orbits in Rotating Second Degree and Order Gravity Fields

Wei-Duo Hu 1, Daniel J. Scheeres 2,

1 School of Astronautics, BeiHang University, Beijing 100083; weiduo.hu@gmail.com

2 Department of Aerospace Engineering, The University of Michigan, Ann Arbor, MI 48109, USA

Periodic orbits in an arbitrary 2nd degree and order uniformly rotating gravity field are studied. We investigate the four equilibrium points in this gravity field. We see that close relation exists between the stability of these equilibria and the existence and stability of their nearby periodic orbits. We check the periodic orbits with non-zero periods. In our searching procedure for these periodic orbits, we remove the two unity eigenvalues from the state transition matrix to find a robust, non-singular linear map to solve for the periodic orbits. The algorithm converges well, especially for stable periodic orbits. Using the searching procedure, which is relatively automatic, we find five basic families of periodic orbits in the rotating second degree and order gravity field for planar motion, and discuss their existence and stability at different central body rotation rates.

Key Words:   celestial / orbital mechanics -- asteroid -- periodic orbit -- resonance
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Two Novel Approaches for Photometric Redshift Estimation based on SDSS and 2MASS

Dan Wang 1,2, Yan-Xia Zhang 1, Chao Liu 1,2 and Yong-Heng Zhao 1

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; dwang@lamost.org

2 Graduate School of Chinese Academy of Sciences, Beijing 100049

We investigate two training-set methods: support vector machines (SVMs) and Kernel Regression (KR) for photometric redshift estimation with the data from the databases of Sloan Digital Sky Survey Data Release 5 and Two Micron All Sky Survey. We probe the performances of SVMs and KR for different input patterns. Our experiments show that with more parameters considered, the accuracy does not always increase, and only when appropriate parameters are chosen, the accuracy can improve. For different approaches, the best input pattern is different. With different parameters as input, the optimal bandwidth is dissimilar for KR. The rms errors of photometric redshifts based on SVM and KR methods are less than 0.03 and 0.02, respectively. Strengths and weaknesses of the two approaches are summarized. Compared to other methods of estimating photometric redshifts, they show their superiorities, especially KR, in terms of accuracy.

Key Words:   galaxies: distances and redshifts -- galaxies: general -- methods: data analysis -- techniques: photometric
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An Approach of Tropospheric Correction for VLBI Phase-Referencing using GPS Data

Bo Zhang 1,2, Xing-Wu Zheng 1, Jin-Ling Li 2 and Ye Xu 3

1 Department of Astronomy, Nanjing University, Nanjing 210093; bozhang@nju.edu.cn

2 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030

3 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008

The dominant source of error in VLBI phase-referencing is the troposphere at observing frequencies above 5GHz. We compare the tropospheric zenith delays derived from VLBI and GPS data at VLBA stations collocated with GPS antennas. The systematic biases and standard deviations both are at the level of sub-centimeter. Based on this agreement, we suggest a new method of tropospheric correction in phase-referencing using combined VLBI and GPS data.

Key Words:   techniques: VLBI -- techniques: GPS -- atmospheric effects -- methods: data analysis -- astrometry
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ChJAA, 2008, Vol.8, No.1

Chinese Journal of Astronomy and Astrophysics: Online Edition


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