B037 is of interest because it is both the most luminous and the most highly reddened cluster known in M31. Deep observations and high spatial resolution images with the Advanced Camera for Surveys on the Hubble Space Telescope （HST） first showed that this cluster is crossed by a dust lane. Photometric data in the F606W and F814W filters obtained in this paper indicate that colors of （F606W - F814W） in the dust lane are redder-0.4 mag than ones in the other regions of B037. The HST images show that this dust lane seems to be contained in B037, instead of in the M31 disk or the Milky Way. As far as we know, the formation of dust requires gas with a rather high metallicity. However, B037 has a low metallicity of [Fe/H] =→1.07 ±0.20. So, it seems improbable that the observed dust lane is physically associated with B037. It is clear that the origin of this dust lane is worthy of future study. In addition, based on these images, we present the precise variation of ellipticity and position angle, and of surface brightness profile, and determine the structural parameters of B037 by fitting a single-mass isotropic King model. In the F606W filter, we derive the best-fitting scale radius r0 = 0.56±0.02＂ （= 2.16±0.08 pc）, a tidal radius rt = 8.6±0.4I＂ （= 33.1±1.5 pc）, and a concentration index c = log（rt/ro） = 1.19±0.02. In the F814W filter, we derive r0 = 0.56 4± 0.01H （_=2.16 ±0.04 pc）, rt = 8.9 ±0.3＂ （= 34.3±1.2 pc）, and c = log（rt/ro） = 1.20±0.01. The extinction-corrected central surface brightness is μ0 = 13.53±0.03 mag arcsec^-2 in the F606W filter, and 12.85±0.03 mag arcsec^-2 in the F814W filter. We also calculate the half-light radius at rh = 1.05±0.03＂（= 4.04±0.12 pc） in the F606W filter and rh =1.07±0.01＂（= 4.12±0.04 pc） in the F814W filter. In addition, we derived the complete magnitudes of B037 in the V and I bands by transforming the magnitudes from the ACS system to the standard system, which are in good agreement with previous ground-based
We present the photometry of 30 globular clusters （GCs） and GC candidates in 15 intermediate-band filters covering the wavelength region from - 3000 to 10000A using the archival CCD images of M31 observed as part of the Beijing - Arizona - Taiwan - Connecticut （BATC） Multicolor Sky Survey. We transform these intermediate-band photometric data into the photometry in the standard U BV RI broadbands. These M31 GC candidates are selected from the Revised Bologna Catalog （RBC V.3.5）, and most of these candidates do not have any photometric data. Therefore, the presented photometric data are a supplement to the RBC V.3.5. We find that 4 out of 61 GCs and GC candidates in RBC V.3.5 do not show any signal on the BATC images at their locations. By applying a linear fit of the distribution in the color-magnitude diagram of blue GCs and GC candidates using data from the RBC V.3.5, in this study, we find the ＂blue-tilt＂ of blue M31 GCs with a high confidence at 99.95% or 3.47cr for the confirmed GCs, and 〉 99.99% or 4.87e for GCs and GC candidates.
An optical photometric observation with the Beijing-Arizona-Taiwan- Connecticut （BATC） multicolor system is carried out for A98 （z =0.104）, a galaxy cluster with two large enhancements in X-ray surface brightness. Spectral energy distributions （SEDs） covering 15 intermediate bands are obtained for all sources detected down to V - 20 mag in a field of 58′× 58′. After star-galaxy separation with colorcolor diagrams, a photometric redshift technique is applied to the galaxy sample for further membership determination. The color-magnitude relation is taken as a further restriction of the early-type cluster galaxies. As a result, a list of 198 faint member galaxies is achieved. Based on the newly generated sample of member galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated in detail. A separate galaxy group, A98X, is also found to the south of the main concentration of A98, which is gravitationally unbound to A98. For 74 spectroscopically confirmed member galaxies, the environmental effect on the star formation history is investigated. The bright galaxies in the core region are found to have shorter time scales of star formation, longer mean stellar ages, and higher interstellar medium metallicities, which can be interpreted in the context of the hierarchical cosmological scenario.
Li ZhangQi-Rong YuanXu ZhouZhao-Ji JiangYan-Bin YangJun MaJiang-Hua WuZhen-Yu Wu
We present metal abundance properties of 144 globular clusters associated with M81. These globulars represent the largest globular cluster sample in M81 till now. Our main results are： the distribution of metallicities is bimodal, with metallicity peaks at [Fe/H] -1.51 and -0.58, and the metal-poor globular clusters tend to be less spatially concentrated than the metal-rich ones; the metal-rich globular clusters in M81 do not demonstrate a centrally concentrated spatial distribution like the metalrich ones in M31 do; like our Galaxy and M31, the globular clusters in M81 have a small radial metallicity gradient. These results are consistent with those obtained from a small sample of M81 globular clusters. In addition, this paper shows that there is evidence that a strong rotation of the M81 globular cluster system around the minor axis exists, and that rotation is present in the metal-rich globular cluster subsample, but the metal-poor globular cluster subsample shows no evidence of rotation. The most significant difference between the rotation of the metal-rich and metal-poor globular clusters occurs at intermediate projected galactocentric radii. Our results confirm the conclusion of Schroder et al. that M81＇s metal-rich globular clusters at intermediate projected radii are associated with a thick disk of M81.
We present a quantitative study of the classification of Extremely Red Objects （EROs）. The analysis is based on the multi-band spatial- and ground-based observations （HST/ACS-BViz, HST/NICMOS-JH, VLT-JHK） in the Hubble Ultra Deep Field （UDF）. Over a total sky area of 5.50 arcmin2 in the UDF, we select 24 EROs with the color criterion （i - K）vega 〉 3.9, corresponding to （I - K）vega 〉 ～4.0, down to Kvega = 22. We develop four methods to classify EROs into Old passively evolving Galaxies （OGs） and Dusty star-forming Galaxies （DGs）, including （i - K） vs. （J - K） color diagram, spectral energy distribution fitting method, Spitzer MIPS 24 um image matching, and nonparametric measure of galaxy morphology, and found that the classification results from these methods agree well. Using these four classification methods, we classify our EROs sample into 60Gs and 8 DGs to KVega 〈 20.5, and 80Gs and 16 DGs to KVega 〈 22, respectively. The fraction of DGs increases from 8/14 at KVega 〈 20.5 to 16/24 at KVega 〈 22. TO study the morphology of galaxies with its wavelength, we measure the central concentration and the Gini coefficient for the 24 EROs in our sample in HST/ACS-i, z and HST/NICMOS-J, H bands. We find that the morphological parameters of galaxies in our sample depend on the wavelength of observation, which suggests that caution is necessary when comparing single wavelength band images of galaxies at a variety of redshifts.
The Andromeda galaxy was observed by the Guoshoujing Telescope （formerly 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. In to- tal, 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 out to about 7 kpc along the major axis. These rotation velocity measurements comple- ment those of the gas content, such as the H I and CO. The radial velocity dispersion shows that the stars in the bulge are more dynamically thermal and the disk is more rotationally-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 spi- ral arms can reach as young as about 1 Gyr. These young stellar populations have a 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.
Hu ZOUYan-Bin YangTian-Meng ZhangJun MaXu ZhouAli LuoHao-Tong ZhangZhong-Rui BaiYong-Heng Zhao
We present the first photometric results in J, H and Ks from 2MASS （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.
Jun Ma 1,21 National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China 2 Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China
