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2.ASS photometry and age estimation of the globular clusters in the outer halo of M31

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Research in Astronomy and Astrophysics 2012年第2期12卷 115-126页

作者： Jun Ma 1,2. national astronomical {2.,chinese academy of sciences,beijing 100012.China 2.Key Laboratory of Optical Astronomy,national astronomical {2.,chinese academy of sciences,beijing 100012.China national astronomical {2. Chinese Academy of Sciences Beijing 100012 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

We present the first photometric results in J, H and Ks from 2.ASS （Two Micron All Sky Survey） imaging of 10 classical globular clusters （GCs） in the far outer regions of M31. Combined with the V and I photometric data from previous literature, we constructed a color-color diagram between J - Ks and V - Ⅰ. By comparing the integrated photometric measurements with evolutionary models, we estimate the ages of these clusters. The results showed that all of these clusters are older than 3 × 109 yr, and among them four are older than 10 Gyr and the other six have intermediate ages between 3 - 8 Gyr. The masses for these outer-halo GCs are from 7.0 × 104 M to 1.02.× 10^6 M. We argued that GC2.and GC3, whose ages, metallicities and distance moduli are almost the same, were accreted from the same satellite galaxy, if they did not form in situ. The statistical results show that the ages and metallicities of these 10 M31 outer-halo GCs do not vary with projected radial position, and a relationship between age and metallicity does not exist.

关键词： galaxies: halos - galaxies: individual (M31) - star clusters: general

A Remark on Using Gravitational Lensing Probability as a Probe of the Central Regions of CDM Halos

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chinese Journal of Astronomy and Astrophysics 2002年第5期2卷 399-407页

作者： YunLinational astronomical {2., chinese academy of sciences, beijing 100012 national astronomical {2. Chinese Academy of Sciences Beijing 100012

We calculate the gravitational lensing probabilities by cold dark matter (CDM) halos with different density profiles, and compare them with current observations from the Cosmic Lens All-Sky Survey (CLASS) and the Jodrell-Bank VLA Astrometric Survey (JVAS). We find that the lensing probability is dramatically sensitive to the clumping of the dark matter, or quantitatively, the concentration parameter. We also find that our predicted lensing probabilities in most cases show inconsistency with the observations. It is argued that high lensing probability may not be an effective tool for probing the statistical properties of inner structures of dark matter halos.

关键词： cosmology: dark matter - gravitational lensing - cosmology:theory - galaxies: halos

A Date Recovery System launched for chronological studies in ancient China

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Science China(Physics,Mechanics & Astronomy) 2008年第1期51卷 105-110页

作者： LI Yong national astronomical {2.,chinese academy of sciences,beijing 100012.China 1. national astronomical {2. Chinese Academy of Sciences Beijing 100012 China

Benefited from the performance of the Xia-Shang-Zhou Chronology Project(XSZP) in China and our new astronomical chronology method designed and processed for chinese particular 60-day-cycle Ganzhi(the heavenly stems and earthly branches)date records,we launch a Date Recovery System(DRS)for ancient China. Of high analysis function,this software can recover and convert the complete or incomplete date information originally from Ganzhi style in the historical period of China to the Gregorian Calendar System,which may have wide applications in the area of literary history,archaeology and cultural relic,etc.,and solve the Goldbach Puzzles of chinese *** an example,we give the detailed process for the sculptures on four bronze wares with the Ganzhi data and afterwards employ this software and provide their possible dates corresponding to Gregorian system.

关键词： chronology date ephemeris software

Testing the Universality of the TIS Model on Cluster Scales from the X-ray Surface Brightness Profiles

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chinese Journal of Astronomy and Astrophysics 2001年第1期1卷 29-38页

作者： Yu-Ying Zhang (beijing astronomical Observatory and {2. astronomical observatories, chinese academy of sciences, beijing 100012. beijing astronomical Observatory and {2. astronomical observatories Chinese Academy of Sciences Beijing 100012

The truncated isothermal sphere (TIS) model has been recently suggested as an alternative for virialized dark halos (Shapiro et al. 1999). Both its profound theoretical motivation and its successful explanations for the galactic rotation curves and the gravitational scaling laws of clusters indicate that the TIS model is a promising candidate among other prevailing models such as the NFW profile and the Burkert profile. This promotes us to re-examine the universality of the TIS model on cluster scales from a different angle. Using an ensemble of X-ray surface brightness profiles of 45 clusters, we test the goodness of fit of the TIS predicted gas distributions to the X-ray data under the assumption of isothermal, hydrostatic equilibrium. Unlike the conventional B model or the NFW/Burkert profile, for which about half of the clusters have the reduced X2.values smaller than 2. the TIS model fails in the fitting of the X-ray surface brightness profiles of clusters in the sense that 38 out of the 45 clusters show X2.> 2. This may constitute a challenge for the universality of the TIS model unless the present analysis is seriously contaminated by other uncertainties including the negligence of non-gravitational heating processes and the unconventional sampling of the X-ray data.

关键词： cosmology: theory -dark matter - galaxies: clusters: general- X-rays: galaxies

Modeling earthquake indexes derived from the earthquake warning system upon the planet earth

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Science China(Physics,Mechanics & Astronomy) 2010年第12期53卷 2293-2299页

作者： LI Yong national astronomical {2., chinese academy of sciences, beijing 100012. China 1. national astronomical {2. Chinese Academy of Sciences Beijing 100012 China

By studying the correlation between historical earthquake data and the distributional characteristics of parameters of solid earth tides in the earthquake epicenter, we are able to design a forecasting function of earthquake probability. We put forward a design method for the Earthquake Warning System. The model could theoretically simulate and be used to predict the probability of strong earthquakes that could occur anywhere at any time. In addition, the system could also conveniently obtain global or partial Modeling Earthquake Indexes to finally combine the precise pointing prediction and forecast of partial indexes. The literature quotes global data values, provided by NEIC, of 1544 M ≥ 6.5 earthquakes. It also gives examples of instantaneous earthquake indexes of the whole world and Taiwan Region on 1st January 2.10, UT=0:00 and the average earthquake index near the Taiwan Region. According to the 10-year pointing prediction of strong earthquakes in San Francisco, the literature provides the average earthquake index on 2.th June 2.15 (± 15 days), in its neighborhood.

关键词： earthquake earthquake warning system astrogeodynamics index

Ionization state of cosmic hydrogen by early stars and quasars

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Research in Astronomy and Astrophysics 2009年第6期9卷 665-681页

作者： Xiao-Chun Mao1,2.1 national astronomical {2., chinese academy of sciences, beijing 100012. China 2.Graduate University of chinese academy of sciences, beijing 100049, China national astronomical {2. Chinese Academy of Sciences Beijing 100012 China Graduate University of chinese academy of sciences Beijing 100049 China

Cosmic hydrogen is reionized and maintained in its highly ionized state by the ultraviolet emission attributed to an early generation of stars and quasars. The Lyα opacity observed in absorption spectra of high-redshift quasars permits more stringent constraints on the ionization state of cosmic hydrogen. Based on density perturbation and structure formation theory, we develop an analytic model to trace the evolution of the ionization state in the post-overlap epoch of reionization, in which the bias factor is taken into account. For quasars, we represent an improved luminosity function by utilizing a hybrid approach for the halo formation rate that is in reasonable agreement with the published measurements at 2.≤ z ≤ 6. Comparison with the classic Press-Schechter mass function of dark matter halos, we demonstrate that the biased mass distribution indeed enhances star formation efficiency in the overdense environment by more than 2. per cent following the overlap of ionized bubbles. In addition, an alternative way is introduced to derive robust estimates of the mean free path for ionizing photons. In our model, star-forming galaxies are likely to dominate the ionizing background radiation beyond z = 3, and quasars contribute equally above a redshift of z ～ 2.5. From 5 ≤ z ≤ 6, the lack of evolution in photoionization rate can thus be explained by the relatively flat evolution in star formation efficiency, although the mean free path of ionizing photons increases rapidly. Moreover, in the redshift interval z ～ 2.- 6, the expected mean free path and Gunn-Peterson optical depth obviously evolve by a factor of ～ 500 and ～50 respectively. We find that the relative values of critical overdensities for hydrogen ionization and collapse could be 430% at z ≈2.and 2. at z ≈6, suggesting a rapid overlap process in the overdense regions around instant quasars following reionization. We further illustrate that the absolute estimates of the fraction of neutral hydrogen computed fr

关键词： cosmology theory -- formation galaxies -- quasars general -- diffuse radiation -- intergalactic medium

Infrared Galaxies in the Nearby Universe

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chinese Journal of Astronomy and Astrophysics 2008年第6期8卷 643-652页

作者： Jian-Ling Wang 1 national astronomical {2.,chinese academy of sciences,beijing 100012.China 2.Graduate School of chinese academy of sciences,beijing 100049,China national astronomical {2. Chinese Academy of Sciences Beijing 100012 China Graduate School of chinese academy of sciences Beijing 100049 China

We used the Sloan Digital Sky Survey （SDSS） Data Release 5 （DR5） to study the morphological properties of 1137 nearby infrared （IR） galaxies, most of which are brighter than 15.9 mag in r-band. This sample was drawn from a cross-correlation of the Infra-Red astronomical Satellite （IRAS） point source catalog redshift survey with DR5 at z ≤ 0.08. Based on this IR galaxy sample, we constructed five volume-limited sub-samples with IR luminosity ranging from 10^9.5 L⊙ to 10^12.⊙. By deriving the IR luminosity functions （LF） for different morphological types, we found that normal spiral galaxies are the dominant population below LIR ~ 8 ~ 10^10 L⊙; while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR ≈ 5 × 10^10L⊙. As the IR luminosity decreases, the IR galaxies become more compact and have lower stellar masses. The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe, while, in contrast, the contribution from peculiar galaxies is only 39%.

关键词： galaxies evolution galaxies interactions galaxies starburst infrared galaxies galaxies luminosity function

Molecular Gas and Dust in the Massive Star Forming Region S 2.3 IR

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chinese Journal of Astronomy and Astrophysics 2004年第5期4卷 440-454页

作者： Rui-Qing Mao and Qin Zeng1 Purple Mountain Observatory, chinese academy of sciences, Nanjing 2.0008 2.national astronomical observatories, chinese academy of sciences, beijing 100012 national astronomical {2. CAS NAOC Beijing 100012 China

The massive star forming region S 2.3 IR is observed in the molecular lines CO J = 2.1, 3–2. NH3 (1,1), (2.2. and the 870 um dust continuum. Four submillimeter continuum sources, labelled SMM 1–4, are revealed in the 870 um dust emission. The main core, SMM1, is found to be associated with a deeply embedded near infrared cluster in the northeast; while the weaker source SMM2.coincides with a more evolved cluster in the southwest. The best fit spectral energy distribution of SMM1 gives an emissivity of β = 1.6, and temperatures of 32.K and 92.K for the cold- and hot-dust components. An SMM1 core mass of 2.6 M☉, and a total mass of 445 M☉ are estimated from the 870 um dust continuum emission. SMM1 is found to have a temperature gradient decreasing from inside out, indicative of the presence of interior heating sources. The total outflow gas mass as traced by the CO J = 3–2.emission is estimated to be 35 M☉. Low velocity outflows are also found in the NH3 (1,1) emission. The non-thermal dominant NH3 line width as well as the substantial core mass suggest that the SMM1 core is a ``turbulent, massive dense core', in the process of forming a group or a cluster of stars. The much higher star formation efficiency found in the southwest cluster supports the suggestion that this cluster is more evolved than the northeast one. Large near infrared photometric variations found in the source PCS-IR93, a previously found highly polarized nebulosity, indicate an underlying star showing the FU Orionis type of behavior.

关键词： ISM: jets and outflows ISM: molecules ISM: dust, extinction stars:formation ISM: individual

The Amplitude of Mass Fluctuations and Mass Density of the Universe Constrained by Strong Gravitational Lensing

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chinese Journal of Astronomy and Astrophysics 2004年第2期4卷 118-124页

作者： Da-Ming Chennational astronomical {2., chinese academy of sciences, beijing 100012.cdm@*** national astronomical {2. Chinese Academy of Sciences Beijing 100012

We investigate the linear amplitude of mass fluctuations in the universe, σ8, and the present mass density parameter of the Universe, Ωm, from statistical strong gravitational lensing. We use the two population model of lens halos with fixed cooling mass scale Mc = 3×1013h-1M⊙ to match the observed lensing probabilities, and leave σ8 orΩm as a free parameter to be constrained by the data. Another varying parameter, the equation of state of dark energy ω, and its typical values of -1, -2.3, -1/2.and -1/3 are investigated. We find that σ8 is degenerate with Ωm in a way similar to that suggested by present day cluster abundance as well as cosmic shear lensing measurements: σ8Ω0.6m≈0.33. However, both σ8≤0.7 and Ωm≤0.2.can be safely ruled out, the best fit is when σ8 = 1.0, Ωm = 0.3 and ω= - 1. This result is different from that obtained by Bahcall & Bode, who gave σ8 = 0.98±0.1 and Ωm = 0.17 ±0.05. For σ8 = 1.0, the higher value ofΩm = 0.35 requires ω = -2.3 and Ωm = 0.40 requires ω= -1/2.

关键词： cosmology: theory - cosmological parameters - gravitational lensing