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
Abstract
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
PDF file (240 KB) |
PS file *.gz (448 KB) |
Back to Contents
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
Abstract
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

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

is not correlated with
B/T and
nB. Both bulge and disk components satisfy a color-magnitude
relation. The

space Fundamental Plane analysis shows that
galaxies with larger
B/T tend to lie tighter and closer to the
line of

+

(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

+

correlates with (
g-
r) color and
B/T, but does not correlate with

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
PDF file (900 KB) |
PS file *.gz (164 KB) |
Tables data (85 KB) |
Back to Contents
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
Abstract
We investigate the

-

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

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 (

) 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

-

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

-

relation than do the radio-quiet
quasars. This deviation is only partly due to a possible
cosmological evolution of the

-

relation and the
luminosity bias. (3) The radio luminosity is proportional to

for radio-quiet quasars and to

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
PDF file (188 KB) |
PS file *.gz (304 KB) |
Back to Contents
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
Abstract
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
PDF file (360 KB) |
PS file *.gz (140 KB) |
Back to Contents
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
Abstract
Extragalactic H
2O 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 H
2O 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,

, 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
PDF file (120 KB) |
PS file *.gz (628 KB) |
Back to Contents
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
Abstract
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
(

) shows a power-law continuum, a silicate emission
feature at 9.7

m, and significant PAH emission features at
7.7, 8.6, 11.3 and 12.7

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 (

) region from the H

luminosity to be

yr
-1, which is consistent
with the result from the Spitzer IRAC 8

m luminosity,

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

erg s
-1, corresponding to
an Eddington ratio (

) 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)
PDF file (388 KB) |
PS file *.gz (520 KB) |
Back to Contents
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
Abstract
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 (

) 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
PDF file (120 KB) |
PS file *.gz ( 80 KB) |
Back to Contents
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
Abstract
We discovered three large HII regions: G148.8+2.3,
G149.5+0.0 and G169.9+2.0 in the Sino-German

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
PDF file (548 KB) |
PS file *.gz (480 KB) |
Back to Contents
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
Abstract:
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
PDF file (468 KB) |
PS file *.gz (620 KB) |
Back to Contents
Modeling
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
Abstract
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

Eri. We adopt different input parameters to
construct models to fit the available observational constraints in,
e.g.,

,
L,
R and [Fe/H]. From the computation we
obtain the average large spacings of

Eri to be about

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:

Eridani
PDF file (380 KB) |
PS file *.gz (236 KB) |
Back to Contents
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
Abstract
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
PDF file (812 KB) |
PS file *.gz (456 KB) |
Back to Contents
ChJAA, 2008, Vol.8, No.5
Chinese Journal of Astronomy and Astrophysics:
Online Edition
http://www.chjaa.org
Copyright 2001--2008 All rights reserved. The National Astronomical
Observatories of
Chinese Academy of Sciences, P.R. China. This Journal or parts thereof,
may not be
reproduced in any form or by any means without written permission from the Copyright owner.
*****
The web version is created and maintained by Aiying Zhou