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MORPHOLOGY OF DWARF GALAXIES IN ISOLATED SATELLITE SYSTEMS
안홍배 한국천문학회 2017 Journal of The Korean Astronomical Society Vol.50 No.4
The environmental dependence of the morphology of dwarf galaxies in isolated satellite systems is analyzed to understand the origin of the dwarf galaxy morphology using the visually classified morphological types of 5836 local galaxies with $z \lesssim 0.01$. We consider six sub-types of dwarf galaxies, dS0, dE, dE$_{bc}$, dSph, dE$_{blue}$, and dI, of which the first four sub-types are considered as early-type and the last two as late-type. The environmental parameters we consider are the projected distance from the host galaxy ($r_{p}$), local and global background densities, and the host morphology. The spatial distributions of dwarf satellites of early-type galaxies are much different from those of dwarf satellites of late-type galaxies, suggesting the host morphology combined with $r_{p}$ plays a decisive role on the morphology of the dwarf satellite galaxies. The local and global background densities play no significant role on the morphology of dwarfs in the satellite systems hosted by early-type galaxies. However, in the satellite system hosted by late-type galaxies, the global background densities of dE and dSph satellites are significantly different from those of dE$_{bc}$, dE$_{blue}$, and dI satellites. The blue-cored dwarf satellites (dE$_{bc}$) of early-type galaxies are likely to be located at $r_{p} > 0.3$ Mpc to keep their cold gas from the ram pressure stripping by the hot corona of early-type galaxies. The spatial distribution of dE$_{bc}$ satellites of early-type galaxies and their global background densities suggest that their cold gas is intergalactic material accreted before they fall into the satellite systems.
ENVIRONMENTAL DEPENDENCE OF WARPS IN SPIRAL GALAXIES
안홍배,배현정 한국천문학회 2016 Journal of The Korean Astronomical Society Vol.49 No.6
We determined the warp parameters of 192 warped galaxies which are selected from 340 edge-on galaxies using color images as well as $r$-band isophotal maps. We derive the local background density ($\Sigma_{n}$) to examine the dependence of the warp amplitudes on the galaxy environment. We find a clear trend that strongly warped galaxies are likely to be found in high density regions where tidal interactions are supposed to be frequent. However, the correlation between $\alpha_{w}$ and $\Sigma_{n}$ is too weak for weakly warped galaxies ($\alpha_{w} < 4^{\circ}$) and the cumulative distributions of weakly warped galaxies are not significantly different from those of galaxies with no detectable warps. This suggests that tidal interactions do not play a decisive role in the formation of weak warps.
Environmental Dependence of Luminosity-Size Relation of Local Galaxies
안홍배 한국지구과학회 2017 한국지구과학회지 Vol.38 No.5
We present the environmental dependence of the luminosity-size relation of galaxies in the local universe (z < 0.01) along with their dependence on galaxy morphology represented by five broad types (E, dEs, S0, Sp, and Irr). The environmental parameters we consider are the local background density and the group/cluster membership together with the clustercenteric distance for the Virgo cluster galaxies. We derive the regression coefficient (β ), i.e., the slope of the line representing the least-squares fitting to the data and the Pearson correlation coefficient (c.c.) representing the goodness of the least-squares fit along with the confidence interval from bootstrap resampling. We find no significant dependence of the luminosity-size relation on galaxy morphology. However, there is a weak dependence of the luminositysize relations on the environment of galaxies, in the sense that galaxies in the low density environment have shallower slopes than galaxies in the high density regions except for elliptical galaxies that show an opposite trend.
ENVIRONMENT DEPENDENCE OF DISK MORPHOLOGY OF SPIRAL GALAXIES
안홍배 한국천문학회 2014 Journal of The Korean Astronomical Society Vol.47 No.1
We analyze the dependence of disk morphology (arm class, Hubble type, bar type) of nearby spiral galaxies on the galaxy environment by using local background density (∑n), project distance (rp), and tidal index (TI) as measures of the environment. There is a strong dependence of arm class and Hubble type on the galaxy environment, while the bar type exhibits a weak dependence with a high frequency of SB galaxies in high density regions. Grand design fractions and early-type fractions increase with increasing ∑n, 1/rp, and TI, while fractions of flocculent spirals and late-type spirals decrease. Multiple-arm and intermediate-type spirals exhibit nearly constant fractions with weak trends similar to grand design and early-type spirals. While bar types show only a marginal dependence on ∑n, they show a fairly clear dependence on rp with a high frequency of SB galaxies at small rp. The arm class also exhibits a stronger correlation with rp than ∑n and TI, whereas the Hubble type exhibits similar correlations with ∑n and rp. This suggests that the arm class is mostly affected by the nearest neighbor while the Hubble type is affected by the local densities contributed by neighboring galaxies as well as the nearest neighbor.
LUMINOSITY PROFILES OF PROMINENT STELLAR HALOS
안홍배,박형욱 한국천문학회 2018 Journal of The Korean Astronomical Society Vol.51 No.4
We present a sample of 54 disk galaxies which have well developed extraplanar structures. We selected them using visual inspections from the color images of the Sloan Digital Sky Survey. ince the sizes of the extraplanar structures are comparable to the disks, they are considered as prominent stellar halos rather than large bulges. A single S\'ersic profile fitted to the surface brightness along the minor-axis of the disk shows a luminosity excess in the central regions for the majority of sample galaxies. This central excess is considered to be caused by the central bulge component. The mean S\'ersic index of the single component model is 1.1\pm0.9$. A double S\'ersic profile model that employs $n=1$ for the inner region, and varying $n$ for the outer region, provides a better fit than the single S\'ersic profile model. For a small fraction of galaxies, a S\'ersic profile fitted with $n=4$ for the inner region gives similar results. There is a weak tendency of increasing $n$ with increasing luminosity and central velocity dispersion, but there is no dependence on the local background density.