arXiv subjects

Suijian Xue

Publications and source records attributed to Suijian Xue.

27 records · Page 2Linked to original sources

arXiv2002

Spectral Energy and Age Distributions for 51 Globular Cluster Candidates

This paper is the fourth in a series presenting spectrophotometry of 51 globular cluster candidates, that were detected by Mochejska et al. in the nearby galaxy M33 using the data collected by the DIRECT project. The frames of M33 in this study were taken as part of the BATC Multicolor Sky Survey. We obtained the spectral energy distributions of these candidates in 13 intermediate-band filters. By comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual & Charlot, we estimated their ages. The BC96 models provide the evolution in time of the spectrophotometric properties of simple stellar populations for a wide range of stellar metallicity. Our results show that half of the candidates are younger than 10^8 years, whose age degeneracy is not pronounced. We also find that globular clusters formed continuously in M33 from ~4*10^6 -- 10^{10} years. Our results are in agreement with Chandar et al., who estimated ages for 35 globular clusters candidates in common by comparing the photometric measurements to integrated colors from theoretical models by Bertelli et al. The Kolmogorov-Smirnov Test shows that the maximum value of the absolute difference of estimated ages between Chandar et al. and us is 0.48, and the significance level probability is 100.00 per cent.

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arXiv2002

15 colour photometry of Landolt SA95 standard star field

In this paper, we present a set of photometric observations in 15 colors of stars in the Landolt covered by the system range from 300 nm to 1000 nm. Visual magnitudes of the stars being studied in the field are from 10th to 20th mag. The observational methodology and the data reduction procedures are described. The relationships between the BATC intermediate-band system and the Landolt UBVRI broad band system are obtained. A catalogue of the photometry has been produced which contains the SEDs of 3613 stars. The electronic form of this catalogue can be accessed at the CDS via anonymous ftp to cdsarc.u-strasbg.fr.

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arXiv2002

Photometric Redshift Determination with the BATC Multicolor System

In this paper, we present the methodology of photometric redshift determination with the BATC 15-color system by using hyperz program. Both simulated galaxies and real galaxies with known redshifts were used to estimate the accuracy of redshifts inferred from the multicolor photometry. From the test with simulated galaxies, the uncertainty in the inferred redshifts is about $0.02\sim0.03$ for a given range of photometric uncertainty of $0.05 \sim 0.10$. The results with the 27 real galaxies are in good agreement with the simulated ones. The advantage of using BATC intermediate-band system to derive redshift is clear through the comparison with the UBVRI broad-band system. The accuracy in redshift determination with BATC system is mainly affected by the selection of filters and the photometric uncertainties in the observation. When we take the limiting magnitudes of the 15 filters into account, we find that redshift can be determined with good accuracy for galaxies with redshifts less than 0.5, using only filters with central wavelengths shorter than 6000 A.

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arXiv2002

Multicolor photometry of 145 of the HII regions in M33

This paper is the first in a series presenting CCD multicolor photometry for 145 HII regions, selected from 369 candidate regions from Boulesteix et al. (1974), in the nearby spiral galaxy M33. The observations, which covered the whole area of M33, were carried out by the Beijing Astronomical Observatory 60/90 cm Schmidt Telescope, in 13 intermediate-band filters, covering a range of wavelength from 3800 to 10000 A. This provides a series of maps which can be converted to a multicolor map of M33, in pixels of 1.7''*1.7''. Using aperture photometry we obtain the spectral energy distributions (SEDs) for these HII regions. We also give their identification charts. Using the relationship between the BATC intermediate-band system used for the observations and the UBVRI broad-band system, the magnitudes in the B and V bands are then derived. Histograms of the magnitudes in V and in B-V are plotted, and the color-magnitude diagram is also given. The distribution of magnitudes in the V band shows that the apparent magnitude of almost all the regions is brighter than 18, corresponding to an absolute magnitude of -6.62 for an assumed distance modulus of 24.62, which corresponds to a single main sequence O5 star, while the distribution of color shows that the sample is blue, with a mode close to -0.05 as would be expected from a range of typical young clusters.

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arXiv2002

Spectral Energy Distributions and Age Estimates of 78 Star Clusters in M33

In this third paper of our series, we present CCD spectrophotometry of 78 star clusters that were detected by Chandar, Bianchi, & Ford in the nearby spiral galaxy M33. CCD images of M33 were obtained as a part of the BATC Color Survey of the sky in 13 intermediate-band filters from 3800 to 10000Å. By aperture photometry, we obtain the spectral energy distributions of these 78 star clusters. As Chandar, Bianchi, & Ford did, we estimate the ages of our sample clusters by comparing the photometry of each object with theoretical stellar population synthesis models for different values of metallicity. We find that the sample clusters formed continuously in M33 from $\sim 3\times10^6$ -- $10^{10}$ years. This conclusion is consistent with Chandar, Bianchi, & Ford. The results also show that, there are two peaks in cluster formation, at $\sim 8\times10^6$ and $\sim 10^9$ years in these clusters.

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arXiv2002

SED, Metallicity and Age of Halo Globular Clusters in M33

In this paper we study the properties of ten halo globular clusters in the nearby spiral galaxy M33. CCD images of M33 were obtained as a part of the BATC Colour Survey of the sky in 13 intermediate-band filters from 3800 to 10000Å. By aperture photometry, we obtain the spectral energy distributions (SEDs) of these globular clusters. We estimate the ages of our sample clusters by comparing the photometry of each object with theoretical stellar population synthesis models for different values of metallicity. Our results suggest that eight of the ten sample halo globular clusters have ``intermediate'' ages, i.e. between 1 and 8 Gyrs.

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arXiv2002

Multicolor photometry of the galaxies in the central region of Abell 2634

An optical photometric observation with the BATC multicolor system is carried out for the central 56' x 56' region of the nearby cluster of galaxies, Abell 2634. We achieved the spectral energy distributions (SEDs) of 5572 sources detected down to $V \sim 20$ mag, including 178 previously known galaxies, with fourteen filters covering a wavelength range from 3600 Å to 10000 Å. After excluding the foreground and background galaxies, a sample of 124 known members is formed for an investigation of the SED properties. Based on the knowledge of SED properties of member galaxies, we performed the selection of faint galaxies belonging to Abell 2634. The color-color diagrams are powerful in the star/galaxy separation, and 359 faint galaxies are selected by their color features. The technique of photometric redshift and color-magnitude correlation for the early-type galaxies are applied for these faint galaxies, and a list of 74 faint member galaxies is achieved. Basis on the enlarged sample of member galaxies, the spatial distribution and color-magnitude relation of the galaxies in core region of Abell 2634 are discussed. We find a tendency that the color index dispersion of the early-type members is larger for the outer region, which might reflect some clues about the environmental effect on the evolution of galaxies in a cluster.

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arXiv2001

SED, Age and Metallicity of Star Clusters in M33

In this paper we present CCD spectrophotometry of the star clusters that were detected by Chandar, Bianchi, & Ford in the nearby spiral galaxy M33, using the images obtained with the Beijing Astronomical Observatory 60/90 cm Schmidt Telescope in 13 intermediate-band filters from 3800 to 10000Å. The observations cover the whole area of M33 with a total integration of 32.75 hours from September 23, 1995 to August 28, 2000. This provides a multi-color map of M33 in pixels of $1.7'' \times 1.7''$. By aperture photometry, we obtain the spetral energy distributions (SEDs) of these star clusters. Using theoretical stellar population synthesis models, we also obtain the distributions of age and metallicity of of these star clusters. These clusters formed continuously from $\sim 3\times10^6$ -- $10^{10}$ years, and have a large span of metallicity from ${\rm {Z}=0.0004}$ to ${\rm {Z}=0.05}$.

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arXiv1998

Ring structure and warp of NGC5907 -- Interaction with dwarf galaxies

The edge-on, nearby spiral galaxy NGC5907 has long been used as the prototype of a ``non-interacting'' warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC5907 close to one of the ring's foci. This suggests the ring material is in orbit around NGC5907. No gaseous component to the ring has been detected either with deep H$α$ images or in Very Large Array (VLA) HI 21-cm line maps. The visible material in the ring has an integrated luminosity <= 10^8 L_sun and its brightest part has a color R-I ~ 0.9. All of these properties are consistent with the ring being a tidally-disrupted dwarf spheroidal galaxy. Second, we find that NGC5907 has a dwarf companion galaxy, PGC54419, projected to be only 36.9 kpc from the center of NGC5907, close in radial velocity (ΔV = 45 km s^{-1}) to the giant spiral galaxy. This dwarf is seen at the tip of the HI warp and in the direction of the warp. Hence, NGC5907 can no longer be considered ``non-interacting,'' but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies.

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