Eon-Chang Sung

The Intrinsic Shapes of Low Surface Brightness Dwarf Irregular Galaxies and Comparison to Other Types of Dwarf Galaxies

In this paper, we measure the ellipticities of 30 low surface brightness (LSB) dwarf irregular (dI) galaxies and compare the ellipticity distribution with that of 80 dwarf elliptical (dEs) and 62 blue-compact dwarfs (BCDs). We find that the ellipticity distribution of LSB dIs is very similar to that of BCDs, and marginally different from that of dEs. We then determine the distribution of intrinsic shapes of dI galaxies and compare this to the distributions of other types of dwarf galaxies under various assumptions. First, we assume that LSB dIs are either all oblate or all prolate, and use a nonparametric analysis to find the best-fitting distribution of intrinsic shapes. With this assumption, we find that the scarcity of nearly circular LSB dIs implies, at the 99% confidence level, that they cannot be a population of randomly oriented oblate or prolate objects, implying that LSB dIs are highly unlikely to be disk-shaped systems. Next, we assume that dIs are triaxial, and use a parametric analysis to find permissible distributions of intrinsic shapes. We find that if the intrinsic axis ratios β and γ are distributed according to a Gaussian with means β0 and γ0 and a common standard deviation of σ, the best-fitting set of parameters for LSB dIs is (β0, γ0, σ) = (0.66, 0.50, 0.15), and the best fit for BCDs is (β0, γ0, σ) = (0.66, 0.55, 0.16), while the best fit for dEs is (β0, γ0, σ) = (0.78, 0.69, 0.24). The dIs and BCDs thus have very similar shape distributions, given this triaxial hypothesis, while the dEs peak at a somewhat more spherical shape. Therefore, our results provide strong observational evidence to support the evolutionary scenario in which the three types of dwarf galaxy have a close relation with each other.

A COMPARISON OF THE INTRINSIC SHAPES OF TWO DIFFERENT TYPES OF DWARF GALAXIES BLUE COMPACT DWARFS AND DWARF ELLIPTICALS

We measure the apparent shapes for a sample of 62 blue compact dwarf galaxies (BCDs) and compare them with the apparent shapes for a sample of 80 dwarf elliptical galaxies (dEs). The BCDs are flatter, on average, than the dEs, but the difference is only marginally significant. We then use both nonparametric and parametric techniques to determine possible distributions of intrinsic shapes for the BCDs. The hypothesis that BCDs are oblate spheroids can be ruled out with a high confidence level (>99%), but the hypothesis that they are prolate spheroids cannot be excluded. The apparent shapes of BCDs are totally consistent with the hypothesis that they are triaxial ellipsoids. If the intrinsic axis ratios β and γ are distributed according to a Gaussian with means β0 and γ0 and standard deviation σ, we find that the best-fitting distribution for BCDs has (β0, γ0, σ) = (0.66, 0.55, 0.16), while that for dEs has (β0, γ0, σ) = (0.85, 0.64, 0.24). Our results are consistent with the hypothesis that BCDs have a close evolutionary relation with dEs.

The properties of early-type galaxies in the Ursa Major cluster

Using SDSS-DR7 and NASA/IPAC Extragalactic Database spectroscopic data, we identify 166 galaxies as members of the Ursa Major cluster with Mr < -13.5 mag. We morphological classify all galaxies by means of carefully inspecting g-, r-, i-band colour and monochromatic images. We show that the Ursa Major cluster is dominated by late-type galaxies, but also contains a significant number of early- type galaxies, particularly in the dwarf regime. We present further evidence for the existence of several subgroups in the cluster, consistent with previous findings. The early-type fraction is found to correlate with the mass of the subgroup. We also investigate environmental effects by comparing the properties of the Ursa Major early-type dwarf galaxies to those of the Virgo cluster. In contrast to the Virgo, the red sequence of the Ursa Major cluster is only sparsely populated in the optical and ultraviolet colour-magnitude relations. It also shows a statistically significant gap between -18 < Mr < -17 mag, i.e. the Ursa Major cluster lacks early-type dwarf galaxies at the bright end of their luminosity function. We discover that the majority of early-type dwarf galaxies in the Ursa Major cluster have blue cores with hints of recent or ongoing star formation. We suggest that gravitational tidal interactions can trigger central blue star forming regions in early-type dwarfs. After that, star formation would only fade completely when the galaxies experience ram pressure stripping or harassment, both of which are nearly absent in the Ursa Major cluster.

UBV I Surface Photometry of the Spiral Galaxy NGC 300 in the Sculptor Group

We present UBVI surface photometry over a 20.5 0 ◊20.5 0 area of the late- type spiral galaxy NGC 300. We have derived isophotal maps, surface brightness profiles, ellipticity profiles, position angle profiles, and color profiles. By merging our I-band measurements with those of Boker et al. based on Hubble Space Telescope observations, we have obtained combined I-band surface brightness profiles for the region 0.02 00 < r < 500 00 and have decomposed the profiles into three components: a nucleus, a bulge, and an exponential disk.

The extended ionized gas around the z = 2.44 radio galaxy MRC 0406–244: the nature of the superbubbles and the optical line brightness asymmetries

In this Letter, we investigate the nature of the dramatic ‘superbubble’ emission structures associated with the z = 2.44 radio galaxy MRC 0406−244, using rest-frame optical spectroscopy and an archival Hubble Space Telescope (HST) Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) image. Based on the optical line ratios and the HST morphology, we conclude that the gas in the superbubbles is photoionized by the obscured active nucleus. We suggest that this type of structure might be related to the spatially extended H I absorbers that are detected in front of many high-z radio galaxies. We also suggest that we may be witnessing the destruction of the extended emission-line region. In addition, we investigate the nature of the emission-line brightness asymmetry in MRC 0406−244: we conclude that this asymmetry is due to an asymmetry in the mass of ionized gas, confirming the scenario of McCarthy, van Breugel & Kapahi, and leading us to reject that of Gopal-Krishna & Wiita.

Korea Microlensing Telescope Network: science cases

We present the science cases with the Korea Microlensing Telescope Network (KMTNet) which consists of three widefield 1.6 m telescopes distributed in Chile, South Africa, and Australia, respectively, providing unique continuous sky coverage with the three telescopes. The primary scientific goal of the KMTNet project is to explore the structure and diversity of planetary systems and variable objects. Since the system is mainly optimized to conduct gravitational microlensing surveys, it will enable detections of very low-mass exoplanets, potentially down to the mass of Mars that are inaccessible by other ground-based techniques. In addition to the primary science, it is possible to conduct a variety of other observational programs with the KMTNet system, including photometric studies of nearby galaxies and galaxy clusters, discovery of supernovae and their follow-up observations, and observations of near-Earth objects. We expect synergies between the KMTNet project with other similar or complementary projects in the southern sky, such as SkyMapper.

2MASS NEAR-IR COLOR-MAGNITUDE DIAGRAM OF THE OLD OPEN CLUSTER KING 11

We study near-infrared properties of the old open cluster King 11, based on the 2MASS photometric data. We determine the location of the red giant clump(RGC) in the (K;J i K) color-magnitude diagram and derive the distance modulus of King 11 to be (m i M)0 = 12.50§0.10 using the mean K magnitude of RGC. From the red giant branch slope i [Fe/H] relation we obtain the metallicity of this cluster, [Fe/H]=i0.17§0.07. The age and interstellar reddening of this cluster are estimated to be log t = 9.48§0.05, E(B i V )=0.90§0.03, by applying Padova isochrone flts to the data.

GROUND-BASED NEAR-INFRARED CENSUS FOR YOUNG STAR CLUSTERS IN THE DWARF STARBURST GALAXY NGC 1569

JHK near-infrared photometry of starclusters in the dwarf irregular/dwarf starburst galaxy NGC 1569 are presented. After adopting several criteria to excludeother sources (foreground stars, backgalaxies, etc.), 154 candidates of star clusters are identified in the near-infraredimages of NGC 1569, which include very young star clusters. Especially, from analysis based on theoretical background, wefound ten very young star clusters near the center of NGC 1569. The total reddening values toward these clusters are estimatedto be A V = 1-9 mag from comparisonwith the theoretical estimates given by the Leitherer et al. (1999)s star cluster model.

NEAR-INFRARED PHOTOMETRIC STUDY OF THE OLD OPEN CLUSTER TRUMPLER 5

We present JHK near-infrared photometric study for the old open cluster (OC) Trumpler 5 (Tr 5), based on the 2MASS data. From the color-magnitude diagrams of Tr 5, we have located the position of the red giant clump (RGC) stars, and used the mean magnitude of the RGC stars in K-band to estimate the distance to Tr 5, d = 3.1±0.1 kpc ((m-M) 0 = 12.46±0.04). From fitting the theoretical isochrones of Padova group, we have estimated the reddening, metallicity, and age : E(B-V ) = 0.64±0.05, [Fe/H] = -0.4 ± 0.1 dex, and t = 2.8 ± 0.2 Gyr (log t = 9.45 ± 0.04), respectively. These parameters generally agree well with those obtained from the previous studies on Tr 5 and confirms that this cluster is an old OC with metallicity being metal-poorer than solar abundance, located in the anti-Galactic center region.

A CCD Photometric Study of Close Binary V445 Cep

CCD photometric light curves for the close binary star V445 Cep. A new photometric solution and absolute physical dimensions of the system were derived by applying the Wilson-Devinney program to our observed light curves and radial velocity curves published by Pych et al. The evolutional status of V445 Cep was found to coincide with those of the general low mass ratio contact binary systems.