• Journal of The Korean Astronomical Society
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• v.37 no.3
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• pp.91-117
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• 2004

We analyze the dependence of the mass-to-light ratio of spiral galaxies on the present star formation rate (SFR), and find that galaxies with high present star formation rates have low mass-to-light ratios, presumably as a result of the enhanced luminosity. On this basis we argue that variations in the stellar content of galaxies result in a major source of intrinsic scatter in the Tully-Fisher relation (TF relation). Ideally one should use a 'population-corrected' luminosity. We have also analyzed the relation between the (maximum) luminous mass and rotational velocity, and find it to have a small scatter. We therefore propose that the physical basis of the Tully-Fisher relation lies in a relationship between the luminous mass and rotational velocity, in combination with a 'well-behaved' relation between luminous and dark matter. This implies that the Tully-Fisher relation is a combination of two independent relations: (i) a relation between luminosity and (luminous) mass, based mainly on the star formation history in galaxies, and (ii) a relation between mass and rotation velocity, which is the outcome of the process of galaxy formation. In addition to a 'population-corrected' Tully-Fisher relation, one may also use the relation between mass and luminosity, and the relation between luminous mass and rotation velocity as distance estimators.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.151-154
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• 1996

We examine the observations of large-scale magnetic fields in the Universe. We begin at the largest scale with clusters of galaxies and work our way down through galaxies and finally to the Milky Way. on which we concentrate in detail. We examine the observations of the Galactic magnetic field, and their interpretation, under the philosophy that the Galactic magnetic field is like that in other spiral galaxies. We use pulsar data. diffuse Galactic synchrotron emission, and starlight polarization data to discuss the Galaxy's global magnetic configuration and the uniform ($B_u$), random ($B_r$), and total ($B_t$) components of the field strength. We find disagreement among conclusions derived from the various data sets and argue that the pulsar data are not the best indicator for large-scale Galactic field. Near the Solar circle, we find that the azimuthal average of $B_t$ is 4.2$\mu$G and we adopt $B_u\~$2.2 and $B_r\~3.6{\mu}G$. $B_t$ is higher in spiral arms, reaching $\~5.9{\mu}G$. $B_t$ is higher for smaller $R_{Gal}$, reaching $\~8.0{\mu}G$ for $R_{Gal}$ = 4.0 kpc. The pattern of field lines is not concentric circles but spirals. The inclination of the magnetic spiral may be smaller than that of the Galaxy's spiral arms if our sample, which refers primarily to the interarm region near the Sun, is representative. However, it is not inconceivable that the local field lines follow the Galaxy's spiral pattern, as is observed in external galaxies.

• Publications of The Korean Astronomical Society
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• v.15 no.spc1
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• pp.1-13
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• 2000

We review the early historical developement of astronomical spectrographs, properties of emission line spectra of HII regions in spiral galaxies, and absorption line features of galactic globular clusters. Emission line spectra of HII regions within three spiral galaxies NGC 300, NGC 1365, and NGC 7793, which were observed from AAT/IPCS, had been analysed, and we discuss the abundances of elements in HII regions and the radial abundace gradients through the galaxies. The radial UBV color variations of two globular clusters, NGC 1851 and NGC 2808, were examined for correlations with radial variations of several absorption lines in the integrated spectra, which were obtained from SAAO 74 inch telescope and image tube spectrograph. Nine giant star's spectra in NGC 3201 were also obtained and analysed for the radial abundance gradients in the globular cluster. The results show that the presence of a radial color gradient in a globular cluster is correlated with the presence of abundance gradients. Finally, we suggest some scientific programs for the new high dispersion spectrograph, which will be installed to the BOAO 1.8m telescope.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.39.2-39.2
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• 2013

We use grid-based hydrodynamic simulations to study star formation history in nuclear rings of barred-spiral galaxies. In our previous study, we concentrated on bar-only galaxies without spirals, finding that the star formation rate (SFR) in a nuclear ring exhibits a strong primary burst at early time before decreasing to below 1 $M_{\odot}/yr$ at late time. The rapid decline is caused by the paucity of the gas in the bar region, due to early massive gas inflows to the nuclear ring. Since star formation in nuclear rings is observed to be sustained for about 1-2 Gyr, this requires mechanisms to supply the gas to the bar regions. In this work, we study the effect of spiral arms on the radial gas inflows and related star formation in the nuclear rings. We show that spiral arms are efficient to remove angular momentum of the gas to cause significant gas inflows to the bar region, provided the patten speed of the arms is much smaller than that of the bar. The inflowing gas is added to a nuclear ring, making the ring SFR episodic over a long period of time. The time interval of multiple bursts of star formation is a few tens to hundred million years, with the mean peak SFR of ${\sim}5M_{\odot}/yr$, consistent with observations of M100.

• Journal of Astronomy and Space Sciences
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• v.22 no.2
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• pp.89-112
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• 2005

We determine the rotation velocities of 108 spiral and irregular galaxies (XV-Sample) from first-order rotation curves from position-velocity maps, based on short 21-cm observations with the Westerbork Synthesis Radio Telescope (WSRT). To test the usual random motion corrections, we compare the global HI linewidths and the rotation velocities, obtained from kinematical fits to two-dimensional velocity fields for a sample of 28 galaxies (RC-Sample), and find that the most frequently used correction formulae (Tully & Fouque 1985) are not very satisfactory. The rotation velocity parameter (the random-motion corrected HI linewidth: W?), derived with these corrections, may be statistically equal to two times the true rotation velocity, but in individual cases the differences can be large. We analyse, for both RC- and XV-Samples, the dependence of the slope of, and scatter in the Tully-Fisher relation on the definition of the rotation velocity parameters- For the RC-Sample, we find that the scatter in the Tully-Fisher relation can be reduced considerably when the rotation velocities derived from rotation curves are used instead of the random-motion corrected global H I linewidths. No such reduction in the scatter is seen for XV-Sample. We conclude that the reduction of the scatter in the Tully-Fisher relation seems to be related to the use of two-dimensional velocity information: accurate rotation velocity and kinematical inclination.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.31.3-32
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• 2021

We quantify the relative role of galaxy environment and bar presence on AGN triggering in face-on spiral galaxies using a volume-limited sample with 0.02 < z < 0.055, Mr < 19.5, and σ > 70 km s-1 selected from Sloan Digital Sky Survey (SDSS) Data Release 7. To separate their possible entangled effects, we divide the sample into bar and non-bar samples, and each sample is further divided into three environment cases of isolated galaxies, interacting galaxies with a pair, and cluster galaxies. The isolated case is used as a control sample. For these six cases, we measure AGN fractions at a fixed central star formation rate and central velocity dispersion, σ. We demonstrate that the internal process of the bar-induced gas inflow is more efficient in AGN triggering than the external mechanism of the galaxy interactions in groups and cluster outskirts. The significant effects of bar instability and galaxy environments are found in galaxies with a relatively less massive bulge. We conclude that from the perspective of AGN-galaxy coevolution, a massive black hole is one of the key drivers of spiral galaxy evolution. If it is not met, a bar instability helps the evolution, and in the absence of bars, galaxy interactions/mergers become important. In other words, in the presence of a massive central engine, the role of the two gas inflow mechanisms is reduced or almost disappears. We also find that bars in massive galaxies are very decisive in increasing AGN fractions when the host galaxies are inside clusters.

• Journal of The Korean Astronomical Society
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• v.36 no.2
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• pp.49-54
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• 2003

CCD observations in V, I and H$\alpha$ for NGC 3389 are used to present photometry of 61 HII regions. Their positions, diameters and absolute luminosities have been determined. The luminosity and size distribution functions of the HII regions in NGC 3389 are discussed.

• Journal of The Korean Astronomical Society
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• v.15 no.1
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• pp.41-48
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• 1982

PDS was used to get the structure of two barred spiral galaxies NGC 1313 and NGC 1365. The result shows that NGC 1365 has both a deep spheroidal component and an exponential disk, but NGC 1313 has only an prominent exponential component. The luminosity profiles indicate that KGC 1313 is in type I and NGC 1365 belongs to type II. The length scales $({\alpha}^{-1})$ were derived from the exponential luminosity distributions as 1.64 kpc for NGC 1313 and 2.49kpc for KGC 1365.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.525-527
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• 2015

We prepare a catalog of the morphological types of 5840 galaxies within z = 0.01. We determine the morphological types by visual inspection using color images from the Sloan Digital Sky Survey (SDSS) DR7. The majority of the sample galaxies are SDSS spectroscopic target galaxies, but we add ~ 900 galaxies whose redshifts are available in the NASA Extra Galactic Database (NED). The fraction of elliptical and lenticular galaxies is ~ 0.06 while spiral galaxies comprise ~ 30% of the sample with a bar fraction of ~ 0.6. About half of sample are dwarf galaxies of which ~ 35% are dwarf elliptical-like galaxies. There is a strong correlation between the morphological types and luminosities of the galaxies, i.e., high luminosities in the early type galaxies and low luminosity in the late type galaxies. The mean luminosity of dwarf elliptical-like galaxies is similar to that of irregular galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.33 no.2
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• pp.22-22
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• 2008