arXiv subjects

Jun Ma

Publications and source records attributed to Jun Ma.

530 records · Page 30Linked to original sources

arXiv2002

Properties of disks and spiral arms along the Hubble sequence

This paper presents some new statistical correlations between the properties of disks and spiral arms with some physical properties of galaxies. Our results show that the thickness of spiral disks tend to diminish along the Hubble sequence in the sense that disks of Sc galaxies are 40% thinner than disks of Sab-Sb galaxies. Moreover, the thinner disks tend also to be bluer. We also find that there exists a correlation between HI linewidths and arm pattern within each Hubble type, which suggests that the arm shape is partially determined by the mass of a galaxy. Total mass luminosity ratios and total mass surface densities also have correlations with pitch angles, i.e., for disks with lower surface densities and lower total mass luminosity ratios, the pitch angles tend to be greater.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

arXiv2001

Negative Magneto-Resistance Beyond Weak Localization in Three-Dimensional Billiards: Effect of Arnold Diffusion

We investigate a semiclassical conductance for ballistic open three-dimensional (3-d) billiards. For partially or completely broken-ergodic 3-d billiards such as SO(2) symmetric billiards, the dependence of the conductance on the Fermi wavenumber is dramatically changed by the lead orientation. Application of a symmetry-breaking weak magnetic field brings about mixed phase-space structures of 3-d billiards which ensures a novel Arnold diffusion that cannot be seen in 2-d billiards. In contrast to the 2-d case, the anomalous increment of the conductance should inevitably include a contribution arising from Arnold diffusion as well as a weak localization correction. Discussions are devoted to the physical condition for observing this phenomenon.

cond-mat.mes-hall↗

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 ${\rm {Z}=0.05}$.

astro-ph↗

arXiv2000

Some statistical properties of spiral galaxies

This paper presents some statistical correlations of 72 northern spiral galaxies. The results show that early-type spirals that are brighter, and thicker, and the axis ratios ($H_{z}/H_r$) of the disk tend to be smaller along the Hubble sequence. We also find that $H_{z}/H_r$ correlates strongly with the galaxy's color, and early-type spirals have larger values of $H_{z}/H_r$. The inclinations obtained by fitting the pattern of a spiral structure with a logarithmic spiral form are nearly the same as those obtained by using the formulas of Aaronson et al. (1980). Finally, the mean measured pitch angles for the different Hubble sequences in the Third Catalogue of Bright Galaxies by de Vaucouleurs et al. (1991) are derived.

astro-ph↗

arXiv2000

Dependence of Spiral Galaxy Distribution on Viewing Angle in RC3

The normalized inclination distributions are presented for the spiral galaxies in RC3. The results show that, except for the bin of $81^{\circ}$-$90^{\circ}$, in which the apparent minor isophotal diameters that are used to obtain the inclinations, are affected by the central bulges, the distributions for Sa, Sab, Scd and Sd are well consistent with the Monte-Carlo simulation of random inclinations within 3-$σ$, and Sb and Sbc almost, but Sc is different. One reason for the difference between the real distribution and the Monte-Carlo simulation of Sc may be that some quite inclined spirals, the arms of which are inherently loosely wound on the galactic plane and should be classified to Sc galaxies, have been incorrectly classified to the earlier ones, because the tightness of spiral arms which is one of the criteria of the Hubble classification in RC3 is different between on the galactic plane and on the tangent plane of the celestial sphere. Our result also implies that there might exist biases in the luminosity functions of individual Hubble types if spiral galaxies are only classified visually.

astro-ph↗