arXiv subjects

Yanbin Yang

Publications and source records attributed to Yanbin Yang.

At least 73 records · Page 4Linked to original sources

arXiv2011

Kinematics and Stellar Population Properties of the Andromeda Galaxy by the Spectroscopic Observations of the Guoshoujing Telescope

The Andromeda galaxy was observed by the Guoshoujing Telescope (GSJT, formly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope -- LAMOST) during the 2009 commissioning phase. Due to the absence of standard stars for flux calibration, we use the photometric data of 15 intermediate bands in the Beijing-Arizona-Taipei-Connecticut (BATC) survey to calibrate the spectra. Total 59 spectra located in the bulge and disk of the galaxy are obtained. Kinematic and stellar population properties of the stellar content are derived with these spectra. We obtain the global velocity field and calculate corresponding rotation velocities outer to about 7 kpc along the major axis. These rotation velocity measurements complement those of the gas content, such as the H {\sc i} and CO. The radial velocity dispersion presents that the stars in the bulge are more dynamically thermal and the disk is more rotation-supported. The age distribution shows that the bulge was formed about 12 Gyr ago, the disk is relatively younger, and the ages of some regions along the spiral arms can reach as young as about 1 Gyr. These young stellar populations have relatively richer abundance and larger reddening. The overall average metallicity of the galaxy approximates the solar metallicity and a very weak abundance gradient is gained. The reddening map gives a picture of a dust-free bulge and a distinct dusty ring in the disk.

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arXiv2011

Stellar Population Properties and Evolution Analysis of NGC 628 with the Panchromatic Photometry

Panchromatic spectral energy distribution (SED) from the ultraviolet (UV), optical to infrared (IR) photometry of NGC 628, combined with the evolutionary stellar population synthesis, is used to derive the spatially resolved age, metallicity and reddening maps. These parameter distributions show that the bulge of this galaxy is a disk-like pseudobulge, which has the S{é}rsic index close to the exponential law, rich gas, and a young circumnuclear ring structure. We also discover the disk has two distinct regions with different radial age and metallicity gradients. The inner region is older and has a much steeper age gradient than the outer region of the disk. Both these two regions and the central young structure can be seen in the radial profile of the optical color. Based on the age and reddening distributions, we consider that the pseudobulge and disk are likely to have grown via the secular evolution, which is the redistribution of mass and energy through the angular momentum transport caused by the non-axisymmetric potential of the spirals. However, possible gas accretion events could affect the outer region of the disk, due to abundant H{\sc i} gas accumulating in the outer disk.

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arXiv2011

Age and mass constraints for a young massive cluster in M31 based on spectral-energy-distribution fitting

VDB0-B195D is a massive, blue star cluster in M31. It was observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey using 15 intermediate-band filters covering a wavelength range of 3000--10,000 Å. Based on aperture photometry, we obtain its spectral-energy distribution (SED) as defined by the 15 BATC filters. We apply previously established relations between the BATC intermediate-band and the Johnson-Cousins $UBVRI$ broad-band systems to convert our BATC photometry to the standard system. A detailed comparison shows that our newly derived $VRI$ magnitudes are fully consistent with previous results, while our new $B$ magnitude agrees to within $2σ$. In addition, we determine the cluster's age and mass by comparing its SED (from 3000 to 20,000Å, comprising photometric data in the 15 BATC intermediate bands, optical broad-band $BVRI$, and 2MASS near-infrared $JHK_{\rm s}$ data) with theoretical stellar population synthesis models, resulting in age and mass determinations of $60.0\pm 8.0$~Myr and $(1.1-1.6) \times 10^5 M_\odot$, respectively. This age and mass confirms previous suggestions that VDB0-B195D is a young massive cluster in M31.

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arXiv2010

Disentangling the morpho-kinematic properties of a face-on merger at z~0.7

At intermediate redshifts, many galaxies seem to be perturbed or suffering from an interaction. Considering that disk galaxies may have formed and evolved through minor mergers or through major mergers, it is important to understand the mechanisms at play during each type of merger in order to be able to establish the outcome of such an event. In some cases, only the use of both morphological and kinematical information can disentangle the actual configuration of an encounter at intermediate redshift. In this work, we present the morphological and kinematical analysis of a system at z=0.74 in order to understand its configuration, interacting stage and evolution. Using the integral field spectrograph GIRAFFE, long-slit spectroscopy by FORS2 and direct optical images from the HST-ACS and ISAAC near-infrared images, we disentangle the morphology of this system, its star-formation history and its extended kinematics in order to propose a possible configuration for the system. Numerical simulations are used to test different interacting scenarii. We identify this system as a face-on disk galaxy with a very bright bar in interaction with a smaller companion with a mass ratio of 3:1. The relevance of kinematical information and the constraints it imposes on the interpretation of the observations of distant galaxies is particularly strengthened in this case. This object is amongst the best example on how one may misinterpret morphology in the absence of kinematical information.

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arXiv2009

EAGLE Spectroscopy of Resolved Stellar Populations Beyond the Local Group

We give an overview of the science case for spectroscopy of resolved stellar populations beyond the Local Group with the European Extremely Large Telescope (E-ELT). In particular, we present science simulations undertaken as part of the EAGLE Phase A design study for a multi--integral-field-unit, near-infrared spectrograph. EAGLE will exploit the unprecedented primary aperture of the E-ELT to deliver AO-corrected spectroscopy across a large (38.5 sq. arcmin) field, truly revolutionising our view of stellar populations in the Local Volume.

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arXiv2009

EAGLE Spectroscopy of Resolved Stellar Populations Beyond the Local Group

Valuable insights into galaxy evolution can be gleaned from studies of resolved stellar populations in the local Universe. Deep photometric surveys have provided tracers of the star-formation histories in galaxies from 0.8-16 Mpc, but without robust chemical abundances and stellar kinematics from spectroscopy, their sub-structures and assembly histories remain hidden from us. In this context, we introduce the EAGLE design study for a multi--integral-field-unit, near-infrared spectrograph for the European Extremely Large Telescope (E-ELT). EAGLE will exploit the unprecedented light-gathering power of the E-ELT to deliver AO-corrected spectroscopy across a large (38.5 sq. arcmin) field, truly revolutionising our view of stellar populations in the Local Volume.

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arXiv2008

A giant bar induced by a merger event at z=0.4?

(Aims) We present a physical model of the formation of J033239.72-275154.7, a galaxy observed at z=0.41 and characterized by a big young bar of size 6 kpc. The study of this system is particularly interesting for understanding the connection between mergers and bars as well as the properties and fate of this system as it relates to disk galaxy formation. (Methods) We compare the morphological and kinematic properties of J033239.72-275154.7, the latter obtained by the GIRAFFE spectrograph, to those derived from the merger of two spiral galaxies described by idealized N-body simulations including a star formation prescription. (Results) We found that the general morphological shape and most of the dynamical properties of the object can be well reproduced by a model in which the satellite is initially put in a retrograde orbit and the mass ratio of the system is 1:3. In such a scenario, a bar forms in the host galaxy after the first passage of the satellite where an important fraction of available gas is consumed in an induced burst. In its later evolution, however, we find that J033239.72-275154.7, whose major progenitor was an Sab galaxy, will probably become a S0 galaxy. This is mainly due to the violent relaxation and the angular momentum loss experienced by the host galaxy during the merger process, which is caused by the adopted orbital parameters. This result suggests that the building of the Hubble sequence is significantly influenced by the last major collision. In the present case, the merger leads to a severe damage of the disk of the progenitor, leading to an evolution towards a more bulge dominated galaxy.

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arXiv2007

The direct oxygen abundances of metal-rich galaxies derived from electron temperature

We aim to derive the electron temperature Te in the gas of metal-rich star-forming galaxies, which can be obtained from their ratios of auroral lines [O II]7320,7330 to nebular lines [O II]3727, in order to establish a more robust mass-metallicity relationship, and compare the Te-based (O/H) abundances with those from empirical strong-line calibrations, such as R23. We obtained 27 spectra by stacking the spectra of several hundred (even several thousand) star-forming galaxies selected from the SDSS-DR4 in each of the 27 stellar mass bins from log(M*) ~8.0 to 10.6 (logMsun). This "stack" method sufficiently improves the signal-to-noise ratio of the auroral lines [O II]7320,7330, which allow us to reliably obtain the electron temperature t2 in the low ionization region from the ratio of [O II]7320,7330 to [O II]3727, then t3 in the high ionization region from t2 by using a relation, and then the direct (O/H) abundances from Te. The results show that the empirical R23 method will overestimate the log(O/H) by 0.2 to 0.6 dex for these moderate metal-rich galaxies. The new metal-mass relationship of the galaxies with moderate metallicities is fitted by a linear fit (12+log(O/H) =6.223+0.231*logM*) confirming that empirical methods significantly overestimate (O/H). We also derived their (N/O) abundance ratios on the basis of the Te method, which are consistent with the combination of the primary and secondary components of nitrogen. For actual use, we re-derive the relations of 12+log(O/H)(Bay) vs. logM* and 12+log(O/H)(Bay) vs. logR23 from the SDSS-DR4 data, which are a bit different from those derived from DR2.

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arXiv2006

Age constraints for an M31 globular cluster from SEDs-fit

We have constrained the age of the globular cluster S312 in the Andromeda galaxy (M31) by comparing its multicolor photometry with theoretical stellar population synthesis models. This is both a check on the age of this globular cluster, as well a check on our methodology. Main-sequence photometry has been the most direct method for determining the age of a star cluster. S312 was observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2003 December. The photometry of BATC images for S312 was taken with 9 intermediate-band filters covering 5000-10000Å. Combined with photometry in the near-ultraviolet (NUV) of {\sl GALEX}, broad-band $UBVR$ and infrared $JHK_s$ of 2MASS, we obtained the accurate spectral energy distributions (SEDs) of S312 from 2267-20000Å. A quantitative comparison to simple stellar population models yields an age of $9.5_{-0.99}^{+1.15}$ Gyr, which is in very good agreement with the previous determination by main-sequence photometry. S312 has a mass of $9.8\pm{1.85}\times 10^5 \rm M_\odot$, and is a medium-mass globular cluster in M31. By analysis of errors of ages determined based on the SED fitting method of this paper, secure age constraints are derived with errors of $< 3$ Gyr for ages younger than 9 Gyr. In fact, the theoretical SEDs are not sensitive to the variation of age for ages greater than $\sim 10$ Gyr. Therefore, for globular clusters as old as the majority of the Galactic GCs, our method do not distinguish them accurately. We emphasize that our results show that even with multiband photometry spanning NUV to $K_s$, our age constraints from SED fitting are distressingly uncertain, which has implications for age derivations in extragalactic globular cluster systems.

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arXiv2006

Evolution of Galaxy Luminosity Function and Luminosity Function by Density Environment at 0.03<z<0.5

Using galaxy sample observed by the BATC large-field multi-color sky survey and galaxy data of SDSS in the overlapped fields, we study the dependence of the restframe $r$-band galaxy luminosity function on redshift and on large-scale environment. The large-scale environment is defined by isodensity contour with density contrast δρ/ρ. The data set is a composite sample of 69,671 galaxies with redshifts 0.03 < z < 0.5 and r < 21.5 mag. The redshifts are composed by three parts: 1) spectroscopic redshifts in SDSS for local and most luminous galaxies; 2) 20-color photometric redshifts derived from BATC and SDSS; 3) 5-color photometric redshifts in SDSS. We find that the faint-end slope αsteepens slightly from -1.21 at z ~ 0.06 to -1.35 at z ~ 0.4, which is the natural consequence of the hierarchical formation of galaxies. The luminosity function also differs with different environments. The value of αchanges from -1.21 at underdense regions to -1.37 at overdense regions and the corresponding M* brightens from -22.26 to -22.64. This suggests that the fraction of faint galaxies is larger in high density regions than in low density regions.

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arXiv2005

Age Estimations of M31 Globular Clusters from Their Spectral Energy Distributions

This paper presents accurate spectral energy distributions (SEDs) of 16 M31 globular clusters (GCs) confirmed by spectroscopy and/or high spatial-resolution imaging, as well as 30 M31 globular cluster candidates detected by Mochejska et al. Most of these candidates have m_V > 18, deeper than previous searches, and these candidates have not yet been confirmed to be globular clusters. The SEDs of these clusters and candidates are obtained as part of the BATC Multicolor Survey of the Sky, in which the spectrophotometrically-calibrated CCD images of M31 in 13 intermediate-band filters from 4000 to 10000 A were observed. These filters are specifically designed to exclude most of the bright and variable night-sky emission lines including the OH forest. In comparison to the SEDs of true GCs, we find that some of the candidate objects are not GCs in M31. SED fits show that theoretical simple stellar population (SSP) models can fit the true GCs very well. We estimate the ages of these GCs by comparing with SSP models. We find that, the M31 clusters range in age from a few ten Myr to a few Gyr old, as well as old GCs, confirming the conclusion that has been found by Barmby et a, Williams & Hodge, Beasley et al., Burstein et al. and Puzia et al. in their investigations of the SEDs of M31 globular clusters.

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arXiv2005

037-B327 in M31: Luminous Globular Cluster or Core of a Former Dwarf Spheroidal Companion to M31?

037-B327 is of interest because it is both the most luminous and the most highly reddened cluster known in M31. Deep observations with the Advanced Camera for Surveys on the Hubble Space Telescope provide photometric data in the F606W band, and also show that this cluster is crossed by a dust lane. We determined the structural parameters of 037-B327 by fitting the observed surface brightness distribution to a King model with r_c=0.72" (=2.69 pc), and r_t=5.87" (=21.93 pc), and a concentration index c=log(r_t/r_c)=0.91. The surface brightness profile appears to be essentially flat within 0.25" of the center and shows no signs of core collapse. Although the dust lane affects the photometry, the King model fits the surface brightness profile well except for the regions badly affected by the dust lane. We also calculate the half-light radius r_h=1.11" (=4.15 pc). Combined with previous photometry, we find that this object falls in the same region of the M_V versus log R_h diagram as do Omega Centauri, M54 and NGC 2419 in the Milky Way and the massive cluster G1 in M31. All four of these objects have been claimed to be the stripped cores of former dwarf galaxies. This suggests that 037-B327 may also be the stripped core of a former dwarf companion to M31.

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arXiv2005

Morphological Dependence of Star Formation Properties for the Galaxies in the Merging Galaxy Cluster A2255

The merging cluster of galaxies A2255 is covered by the Sloan Digital Sky Survey (SDSS) survey. In this paper we perform a morphological classification on the basis of the SDSS imaging and spectral data, and investigate the morphological dependence of the star formation rates (SFRs) for these member galaxies. As we expect, a tight correlation between the normalized SFR by stellar mass (SFR/M$_*$) and the H$α$ equivalent width is found for the late-type galaxies in A2255. The correlation of SFR/M$_*$ with the continuum break strength at 4000 Åis also confirmed. The SFR/M$_*$ - M$_*$ correlation is found for both the early- and late-type galaxies, indicating that the star formation activity tends to be suppressed when the assembled stellar mass M$_*$) increases, and this correlation is tighter and steeper for the late-type cluster galaxies. Compared with the mass range of field spiral galaxies, only two massive late-type galaxies with M$_*>10^{11}$ M$_{\odot}$ are survived in A2255, suggesting that the gas disks of massive spiral galaxies could have been tidally stripped during cluster formation. Additionally, the SFR variation with the projected radial distance are found to be heavily dependent upon galaxy morphology: the early-type galaxies have a very weak inner decrease in SFR/M$_*$, while the inner late-type galaxies tend to have higher SFR/M$_*$ values than the outer late-types. This may suggest that the galaxy-scale turbulence stimulated by the merging of subclusters might have played different roles on early- and late-type galaxies, which leads to a suppression of the star formation activity for E/S0 galaxies and a SFR enhancement for spiral and irregular galaxies.

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arXiv2005

The Progenitor of Supernova 2004dj in a Star Cluster

The progenitor of type II-plateau supernova (SN) 2004dj is identified with a supergiant in a compact star cluster known as "Sandage Star 96" (S96) in the nearby spiral galaxy NGC 2403, which was fortuitously imaged as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from Feb 1995 to Dec 2003 prior to SN 2004dj. The superior photometry of BATC images for S96, taken with 14 intermediate-band filters covering 3000-10000Å, unambiguously establishes the star cluster nature of S96 with an age of $\sim 20$Myr, a reddening of $\hbox{E}(B-V)\sim 0.35$ mag and a total mass of $\sim 96,000$M$_{\odot}$. The compact star cluster nature of S96 is also consistent with the lack of light variations in the past decade. The SN progenitor is estimated to have a main-sequence mass of $\sim$12M$_{\odot}$. The comparison of our intermediate-band data of S96 with the post-outburst photometry obtained as the SN has significantly dimmed, may hopefully conclusively establish the nature of the progenitor.

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arXiv2005

Color and Metallicity Distributions of M81 Globular Clusters

In this paper we present catalogs of photometric and spectroscopic data for M81 globular clusters (GCs). The catalogs include B- and V- photometric and reddening data of 95 GCs, and spectroscopic metallicities of 40 GCs in M81. Using these data, we make some statistical correlations. The results show that the distributions of intrinsic B and V colors and metallicities are bimodal, with metallicity peaks at [Fe/H]=-1.45 and -0.53, respectively as has been demonstrated for our Milky Way and M31. The relation between spectroscopic metallicity and intrinsic B and V color also exists as it does for the Milky Way and M31.

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arXiv2005

Merger Dynamics of the Pair of Galaxy Clusters -- A399 and A401

Convincing evidence of a past interaction between two rich clusters A399 and A401 was recently found by the X-ray imaging observations. In this paper we examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm has been applied to obtain a robust partition into two clusters, which allows us to discuss the virial mass and velocity distribution for each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of $5.4h^{-1}$ Mpc are currently expanding at 583 km/s along the direction with a projection angle of 67.5 degree, and they will reach a maximum extent of $5.65h^{-1}$ Mpc in about $1.0h^{-1}$ Gyr.

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arXiv2004

Chandra X-ray Analysis of Galaxy Cluster A168

We present Chandra X-ray observations of galaxy cluster A168 (z=0.045). Two X-ray peaks with a projected distance of 676 kpc are found to be located close to two dominant galaxies, respectively. Both peaks are significantly offset from the peak of the number density distribution of galaxies. This suggests that A168 consists of two subclusters, a northern subcluster (A168N) and a southern subcluster (A168S). Further X-ray imaging analysis reveals that (1) the X-ray isophotes surrounding the two X-ray peaks are heavily distorted, (2) an elongated and ontinuous filament connects the two X-ray peaks. These suggest that strong interactions have occurred between the two subclusters. Spectral analysis shows that A168 has a mean temperature of 2.53 +/- 0.09 keV and a mean metallicity of 0.31 +/- 0.04 Z_{solar}. The metallicity is roughly a constant across the cluster but the temperature shows some systematic variations. Most X-ray, optical and radio properties of A168 are consistent with it being an off-axis merger several Gyrs after a core passage, although detailed numerical simulations are required to see whether the observed properties, in particular the significant offset between the optical and X-ray centers, can be reproduced in such a scenario.

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arXiv2003

Large-Field Multicolor Study of Abell 168 : Subclusters, Dynamics and Luminosity Functions

This paper presents a multicolor study of the nearby cluster of galaxies Abell 168 (z=0.045) with 13 intermediate-band filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) filter system. After a cross-identification between the photometric data obtained from the BATC and the Sloan Digital Sky Survey (SDSS), a catalog containing 1553 galaxies down to r'<20.0 mag is achieved, which includes 121 spectroscopically confirmed member galaxies. The technique of photometric redshift has been applied to all these galaxies with combined 18-band (13 from BATC and 5 from SDSS) spectral energy distributions (SEDs), in order to perform a faint membership selection in Abell 168. As a result, 255 galaxies are newly selected as the member candidates. Based on the enlarged sample of cluster galaxies, the spatial distribution and dynamics of Abell 168 are investigated. In the light of the spatial distribution of the member galaxies and the 0.2-3.5 keV X-ray image by Einstein observatory, it seems that Abell 168 consists of two merging subclusters with a relative radial velocity of 264 +/- 142 km/s. With the help of ROSTAT software, a detailed investigation of the dynamics shows the intrinsic difference in the velocity distributions for these two subclusters. Under a linear two-body model, they are found to be a gravitationally bound system with 92% probability. The slight deviation of the local velocity distribution from the overall distribution in the central region may suggest a picture of head-on collision in the projection plane. By using a double Schechter function, the close examination of the luminosity functions reveals the different galaxy content of these two subclusters, which implies the merging process is possibly at the early stage.

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