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

2008, Vol.8, No.5 (October 20, 2008)




Extragalactic Astronomy

Galactic Structure and Dynamics

Instruments, Observational Techniques and Data Processing


Astrometry and Celestial Mechanics


Resolving the Mass Discrepancy between Strong and Weak Lensing Methods

Qian Zheng

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; zq@bao.ac.cn

We readdress the outstanding cluster mass discrepancy between strong and weak gravitational lensing techniques utilizing updated data of both giant arcs and weak lensing measurements from the literature. We find that the systematically higher values of cluster masses revealed by strong lensing can be attributed to the oversimplification of the lensing model when estimating the cluster mass enclosed within the giant arcs. This arises because inhomogeneities and substructures in the central cores of clusters may invalidate the spherical symmetry assumption used widely in previous applications. When a more realistic modeling of the arcs is used, then the masses by strong lensing agree fairly well with those given by weak lensing when both are extrapolated to the same cluster regions. We conclude that as of now no significant discrepancy has been found among different cluster mass estimators including optical galaxies, X-ray gas and lensing.

Key Words:   cosmology: gravitational lensing -- galaxies: clusters

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Structural Properties of Early-Type Galaxies from the SDSS DR2

Feng-Shan Liu 1,2,3, Zu-Gan Deng 2, Hong Wu 1 and Xiao-Yang Xia 3

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; lfs@bao.ac.cn

2 Graduate School of Chinese Academy of Sciences, Beijing 100049, China

3 Department of Physics, Tianjin Normal University, Tianjin 300074, China

Two-dimensional bulge/disk light decomposition with GIM2D in both the r- and g-bands has been applied to a sample of 129 early-type galaxies brighter than 13.5 magnitude in the r-band, selected from the Sloan Digital Sky Survey Data Release 2. Intensity-weighted Fourier coefficient $\langle
a_4/a\rangle$ was also derived for each sample galaxy. Our analysis shows that there are correlations between bulge-to-total light ratio (B/T) with bulge Sérsic index nB and between bulge and disk scale sizes. Isophotal shape parameter $\langle
a_4/a\rangle$ is not correlated with B/T and nB. Both bulge and disk components satisfy a color-magnitude relation. The $\kappa$ space Fundamental Plane analysis shows that galaxies with larger B/T tend to lie tighter and closer to the line of $\kappa_1$ + $\kappa_2=8$ (the so-called ``zone of avoidance'') than the galaxies with smaller B/T. It indicates that existence of the disk component may lead to scatter of the distribution on the Fundamental Plane. Our analysis also shows that $\kappa_1$ + $\kappa_2$ correlates with (g-r) color and B/T, but does not correlate with $\langle
a_4/a\rangle$ for early-type galaxies. The fitted parameters and other retrieved parameters used in this paper for all sample galaxies are available online.

Key Words:   galaxies: elliptical and lenticular, cD -- galaxies; photometry -- galaxies; structure -- galaxies

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Radio Luminosity, Black Hole Mass and Eddington Ratio for Quasars from the Sloan Digital Sky Survey

Wei-Hao Bian 1,2, Yan-Mei Chen 2, Chen Hu 3, Kai Huang 1 and Yan Xu 1

1 Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210097, China; bianwh@ihep.ac.cn

2 Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China

3 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China

We investigate the $\mbh$-$\sigma_*$ relation for radio-loud quasars with redshift z<0.83 in Data Release 3 of the Sloan Digital Sky Survey (SDSS). The sample consists of 3772 quasars with better models of the H$\beta$ and lines and available radio luminosity, including 306 radio-loud quasars, 3466 radio-quiet quasars with measured radio luminosity or upper-limit of radio luminosity (181 radio-quiet quasars with measured radio luminosity). The virial supermassive black hole mass () is calculated from the broad line, and the host stellar velocity dispersion ($\sigma_*$) is traced by the core gaseous velocity dispersion. The radio luminosity and radio loudness are derived from the FIRST catalog. Our results are as follows: (1) For radio-quiet quasars, we confirm that there is no obvious deviation from the $\mbh$-$\sigma_*$ relation defined for inactive galaxies when the uncertainties in and the luminosity bias are concerned. (2) We find that the radio-loud quasars deviate more from the $\mbh$-$\sigma_*$ relation than do the radio-quiet quasars. This deviation is only partly due to a possible cosmological evolution of the $\mbh$-$\sigma_*$ relation and the luminosity bias. (3) The radio luminosity is proportional to $\mbh^{1.28^{+0.23}_{-0.16}}(\lb/\ledd)^{1.29^{+0.31}_{-0.24}}$ for radio-quiet quasars and to $\mbh^{3.10^{+0.60}_{-0.70}}(\lb/\ledd)^{4.18^{+1.40}_{-1.10}}$ for radio-loud quasars. The weaker dependence of the radio luminosity on the mass and the Eddington ratio for radio-loud quasars shows that other physical effects would account for their radio luminosities, such as the spin of the black hole.

Key Words:   quasars: emission lines -- galaxies: nuclei -- galaxies: bulges -- black hole physics

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Feedback of Active Galactic Nuclei in Seyfert 2 Galaxies

En-Peng Zhang 1, Wei-Hao Bian 2,3, Chen Hu 1, Wei-Ming Mao 1, A-Li Luo 1 and Yong-Heng Zhao 1

1 National Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, China; zhangep@ihep.ac.cn

2 Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210097, China

3 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China

It is well accepted that feedback from active galactic nuclei (AGNs) plays an important role in the coevolution of the supermassive black hole (SMBH) and its host galaxy, but the concrete mechanism of feedback remains unclear. A considerable body of evidence suggests that AGN feedback suppresses star formation in the host galaxy. We assemble a sample of Seyfert 2 galaxies with recent observational data of compact nuclear starbursts and estimate the gas surface density as a function of column density to illuminate the relation between feedback and AGN properties. Although there are some uncertainties, our data still imply the deviation from the star formation law (Kennicutt-Schmidt law). Further, they indicate that: (1) Feedback correlates with the Eddington ratio, rather than with the mass of SMBH, as a result of decreasing star formation efficiency. (2) The SMBH and the torus are probably undergoing coevolution. Conclusions presented here can be refined through future high resolution CO or HCN observations.

Key Words:   galaxies: active -- galaxies: Seyfert -- feedback

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Extragalactic H2O Megamaser Sources: Central Black Holes, Nuclear X-ray and Maser Emissions

Jiang-Bo Su, Jiang-Shui Zhang and Jun-Hui Fan

Center for Astrophysics, Guangzhou University, Guangzhou 510006, China; jszhang@gzhu.edu.cn

Extragalactic H2O megamasers are typically found within the innermost few parsecs of active galaxy nuclei (AGN) and the maser emission is considered to be excited most likely by the X-ray irradiation of the AGN. We investigate a comprehensive sample of extragalactic H2O masers in a sample of 38 maser host AGN to check potential correlations of the megamaser emission with parameters of the AGN, such as X-ray luminosity and black hole (BH) masses. We find a relation between the maser luminosities and BH masses, $L_{\rm H_{2}O} \propto M_{\rm
BH}^{3.6 \pm 0.4}$ , which supports basically the theoretical prediction. The relation between the maser emission and X-ray emission is also confirmed.

Key Words:   galaxies: active -- galaxies: nuclei -- masers

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Circumnuclear Star Forming Activity in NGC 3982

Shui-Nai Zhang, Qiu-Sheng Gu and Yi-Peng Wang

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

We present a study of the nearby Seyfert galaxy NGC 3982 using optical, infrared and X-ray data acquired by SDSS, Spitzer and Chandra. Our main results are as follows: (1) A simple stellar population synthesis on the nuclear and circumnuclear SDSS spectra gives unambiguous evidence of young stellar components in both the nuclear and circumnuclear regions. (2) The Spitzer Infrared Spectrograph (IRS) spectrum of the central region ($\sim3''$) shows a power-law continuum, a silicate emission feature at 9.7$\mu$m, and significant PAH emission features at 7.7, 8.6, 11.3 and 12.7$\mu$m, suggesting the coexistence of AGN and starburst activities in the central region of NGC 3982. (3) We estimate the star formation rate (SFR) of the circumnuclear ( $\sim
5''-20''$) region from the H$\alpha$ luminosity to be ${\rm
SFR}_{\rm H\alpha} = 0.52 M_\odot$ yr-1, which is consistent with the result from the Spitzer IRAC 8$ \mu$m luminosity, ${\rm
SFR}_{\rm 8.0 \mu m} = 0.57 M_\odot$ yr-1. (4) We measure the spectral energy distribution for the active nucleus of NGC 3982 from radio to X-ray, and obtain a bolometric luminosity of $L_{\rm bol} = 4.5 \times 10^{42}$ erg s-1, corresponding to an Eddington ratio ( $L_{\rm bol}/L_{\rm Edd}$) of 0.014. The HST image of NGC 3982 shows a nuclear mini-spiral between the circumnuclear star-forming region and the nucleus, which could be the channel through which gas is transported to the supermassive black hole from the circumnuclear star-forming region.

Key Words:   galaxies: Seyfert -- galaxies: starburst -- galaxies: nuclei -- galaxies: individual (NGC 3982)

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The Structure of the Galactic Halo

Cui-Hua Du 1,2, Zhen-Yu Wu 2, Jun Ma 2 and Xu Zhou 2

1 College of Physical Sciences, Graduate School of Chinese Academy of Sciences, Beijing 100049, China; ducuihua@gucas.ac.cn

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

We used the star counts in 21 BATC fields obtained with the National Astronomical Observatories (NAOC) 60/90cm Schmidt Telescope to study the structure of the Galactic halo. Adopting a de Vaucouleurs r1/4 law halo, we found that the halo is somewhat flatter ($c/a \sim 0.4$) towards the Galactic center than in the anticentre and antirotation direction (c/a> 0.4). We also notice that the axial ratios are smaller (flatter) towards the low latitude fields than the high latitude fields, except for a few fields. We provide robust limits on the large-scale flattening of the halo. Our analysis shows that the axial ratio of the halo may vary with distance and the observation direction. At large Galactocentric radii, the halo may not have a smooth density distribution, but rather, it may be largely composed of overlapping streams or substructures, which provides a support for the hybrid formation model.

Key Words:   Galaxy: structure -- Galaxy: halo -- Galaxy: fundamental parameters -- Galaxy: formation
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Discovery of Three Large HII Regions in the Galactic Plane

Wei-Bin Shi1,2, Xiao-Hui Sun1, Jin-Lin Han1, Xu-Yang Gao1 and Li Xiao1

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; hjl@bao.ac.cn

2 Department of Space Science and Applied Physics, Shandong University at Weihai, Weihai 264209, China

We discovered three large HII regions: G148.8+2.3, G149.5+0.0 and G169.9+2.0 in the Sino-German $\lambda$6 cm polarization survey of the Galactic plane. They have been identified based on the flat spectral indexes and the strong infrared emission properties.

Key Words:   radio continuum: general -- methods: observational -- HII regions

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The Vignetting Effect of a LAMOST-Type Schmidt Telescope

Yuan Xue and Huo-Ming Shi

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; hmshi@lamost.org


Optical vignetting of a Schmidt reflector is caused mainly by the spherical primary mirror not being big enough and by the effective light-collecting area of the corrector, which depends on the direction of the star light. Calculations of the vignetting of LAMOST, a special reflecting Schmidt telescope, are made by ray-tracing methods. The results show various features due to LAMOST's structure and observing modes. The un-vignetted field is small compared with its field of view. In the outmost portions of the field vignetting increases rapidly with the distance to the field center. The vignetting at a general position within the field of view is a function of both its distance to the field center and its position angle. Vignetting varies when the telescope points at different declinations and during observations. There is difference in vignetting between direct imaging and multi-fiber spectroscopy. Vignetting distorts the relative intensity of celestial objects at different positions in a field and also affects accurate sky-estimation and sky-subtraction. The determined vignetting functions may be used to correct the vignetting effect; alternatively flat-fielding may be adopted for the calibration. The effective apertures, which affect the signal-to-noise ratio of the observations, depend on the different declinations the telescope is pointing at and also different positions within a field due to vignetting.

Key Words:   telescope -- methods: miscellaneous

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Modeling $\epsilon$ Eri and Asteroseismic Tests of Element Diffusion

Ning Gai 1,3, Shao-Lan Bi2,1 and Yan-Ke Tang1,3

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

2 Department of Astronomy, Beijing Normal University, Beijing 100875, China

3 Graduate School of Chinese Academy of Sciences, Beijing 100049, China

Taking into account the helium and metal diffusion, we explore the possible evolutionary status with a seismic analysis, of the MOST (Microvariability and Oscillations of STars) target: the star $\epsilon$ Eri. We adopt different input parameters to construct models to fit the available observational constraints in, e.g., $T_{\rm eff}$, L, R and [Fe/H]. From the computation we obtain the average large spacings of $\epsilon$ Eri to be about $194\pm 1 \mu$Hz. The age of the diffused models was found to be about 1Gyr, which is younger than the age determined previously by models without diffusion. We found that the effect of pure helium diffusion on the internal structure of the young low-mass star is slight, but that of metal diffusion is obvious. The metal diffusion leads the models to have much higher temperature in the radiative interior, and, correspondingly a higher sound speed there, hence a larger frequency and spacings.

Key Words:   stars: evolution -- stars: interiors -- stars: individual: $\epsilon$ Eridani

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Application of Accelerometer Data in Precise Orbit Determination of GRACE -A and -B

Dong-Ju Peng 1,2 and Bin Wu 1

1 Shanghai Astronomical Observatory, CAS, Shanghai 200030, China; pdongju@shao.ac.cn

2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China

We investigate how well the GRACE satellite orbits can be determined using the on-board GPS data combined with the accelerometer data. The preprocessing of the accelerometer data and the methods and models used in the orbit determination are presented. In order to assess the orbit accuracy, a number of tests are made, including external orbit comparison, and through Satellite Laser Ranging (SLR) residuals and K-band ranging (KBR) residuals. It is shown that the standard deviations of the position differences between the so-called precise science orbits (PSO) produced by GFZ, and the single-difference (SD) and zero-difference (ZD) dynamic orbits are about 7cm and 6cm, respectively. The independent SLR validation indicates that the overall root-mean-squared (RMS) errors of the SD solution for days 309-329 of 2002 are about 4.93cm and 5.22cm, for GRACE-A and B respectively; the overall RMS errors of the ZD solution are about 4.25cm and 4.71cm, respectively. The relative accuracy between the two GRACE satellites is validated by the KBR data to be on a level of 1.29cm for the SD, and 1.03cm for the ZD solution.

Key Words:   celestial mechanics -- ephemerides -- methods: numerical

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ChJAA, 2008, Vol.8, No.5

Chinese Journal of Astronomy and Astrophysics: Online Edition


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