• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.65.1-65.1
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• 2020

We present high-resolution, high-sensitivity continuum data of NGC 4522 observed at 3 cm (X-band) and 10 cm (S-band) in full polarization mode using the JVLA. This observation has 2 - 4 times better spatial resolution and 2 - 5 times better sensitivity compared to previous continuum observations. NGC 4522 is a Virgo spiral galaxy undergoing active ram pressure stripping. This galaxy is particularly well known for the CO emission detected outside its stellar disk, some of which coincides with the extraplanar HI gas and Halpha patches. The major goal of our JVLA observation is to leverage our understanding of the influence of the ram pressure on the general ISM field and multi-phase medium. By combining our new deep radio continuum data and previous observations, we will investigate how the B-field properties can be affected by the ram pressure, and what roles the B-field plays in the stripping process of the multi-phased ISM and in the star formation activity when the ram pressure is present.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.77.1-77.1
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• 2014

Galactic spiral arms are abundant with interesting gaseous substructures. It has been suggested that arm substructures arise from the wiggle instability (WI) of spiral shocks. While the nature of the WI remained elusive, our recent work without considering magnetic fields shows that the WI is physically originated from the accumulation of potential vorticity (PV) generated by deformed shock fronts. To elucidate the characteristics of the WI in more realistic galactic situations, we extend our previous linear stability analysis of spiral shocks by including magnetic fields. We find that magnetic fields reduce the amount of density compression at shocks, making the shock fronts to move toward the upstream direction. Magnetic tension forces from bent field lines stabilize the WI by prevent the generation of PV. When the spiral-arm forcing is F=5% of the centrifugal force of galaxy rotation, the maximum growth rate of the WI is found to be about 1.0, 0.4, and 0.2 times the orbital angular frequency for the plasma parameter ${\beta}=100$, 10, and 5, respectively. Shocks with ${\beta}=1$ are stable to the WI for F=5%, while becoming still unstable when F=10%.

• The Bulletin of The Korean Astronomical Society
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• v.28 no.2
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• pp.88-88
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• 2003

• Publications of The Korean Astronomical Society
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• v.14 no.1
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• pp.1-8
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• 1999

We performed VRI CCD surface photometry of three spiral galaxies of HCG10 in order to understand the effect of interactions in the compact group. The morphology of the largest member NGC 536 seems to be normal but its bulge is thought to be of an oblate spheroid. The central surface brightness of the disk of NGC 536 is much fainter than that of disks of nearby spiral galaxies. The morphologies of NGC 531 and NGG 542 appear to be affected by interactions which lead to a warped disk in NGC 531 and a slightly bent disk in NGC 542. NGC 531 have a boxy bulge and a Freeman Type II disk both of which strongly suggest the presence of a bar in the galaxy. There is a break in the slope of the luminosity profile of NGC 542 which is dominated by the disk component.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.257-258
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• 2012

With AKARI, we carried out near-infrared spectroscopy of the nearby barred spiral galaxy, NGC 1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the galactic center region. As a result, we obtain the spatial distributions of the polycyclic aromatic hydrocarbon $3.3{\mu}m$ and the aliphatic hydrocarbon $3.4-3.6{\mu}m$ emission. The former is detected from all the observed regions and the latter is enhanced near the bar connecting the ring with the nucleus. In addition, we detect absorption features due to $H_2O$ ice and CO/SiO at the ring and the galactic center, while we detect the hydrogen recombination line $Br{\alpha}$ only from the ring. Hence the observed spectra change dramatically within the central 1 kpc region.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.34.2-34.2
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• 2015

We aim to investigate the formation of primordial globular clusters (GCs) in the isolated dwarf galaxy (${\sim}10^{10}M_{sun}$) with cosmological zoom-in simulations. For this, we modified cosmological hydrodynamic code, GADGET-3, in a way to include the radiative heating/cooling that enables gas particles cool down to T~10K, reionization (z < 8.9) of the Universe, UV shielding ($n_{shield}$ > $0.014cm^{-3}$), and star formation. Our simulation starts in a cubic box of a side length 1Mpc/h with 17 million particles from z = 49. The mass of each dark matter (DM) and gas particle is $M_{DM}=4.1{\times}10^3M_{sun}$ and $M_{gas}=7.9{\times}10^2M_{sun}$, respectively, thus the GC candidates can be resolved with more than hundreds particles. We found the following results: 1) mini halos with the more interactions before merging into the main halo form the more stars and thus have the higher star mass fraction ($M_{star}/M_{total}$), 2) the mini halos with the high $M_{star}/M_{total}$ can survive longer and thus spiral into closer to the galactic center, 3) the majority of them spiral into bulge, but some of them can survive until the last as baryon-dominated system, like the GC.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.61.2-61.2
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• 2014

A non-axisymmetric mass distribution of galactic structures including bulge (or bar) causes gas inflow from the disk to the nuclear region, including intense star formation within few hundred parsecs of galactic central. In order to investigate the relation between the ellipticity of the bulge and the presence of a nuclear starburst, we use a volume-limited sample of galaxies with Mr < -19.5 mag at 0.02 < z < 0.05 from the Sloan Digital Sky Survey Data Release 7. Total sample is 3252 spiral galaxies, which include nuclear starburst galaxies. We find that the occurrence of nuclear starbursts has a moderate correlation with bulge ellipticity of intermediate-type spiral galaxies (morphology classes Sab-Sb) in low galaxy number density environments and isolated regions where the distance between the target galaxies and the closest galaxies is relatively far. In high galaxy number density environments and interacting regions, close encounters and mergers between galaxies can cause gas inflow to the nuclear region even without the presence of non-axisymmetric bulges.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.68.1-68.1
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• 2014

M74 is a nearby face-on spiral galaxy that hosts three core-collapse supernovae (SNe) : SN Ic 2002ap, SN II-P 2003gd, and SN II-P 2013ej. Therefore it is an ideal target to investigate the properties of the core-collapse SNe and to improve the calibration of Type II-P SNe as a standardizable candle. However, its distance is not well known. We present a new distance estimate to M74 based on the tip of the red giant branch (TRGB). From the photometry of archival F555W and F814W images taken with the Hubble Space Telescope, we derive the TRGB to be at $ITRGB=26.13{\pm}0.02$ and the distance modulus to be $30.04{\pm}0.04$ (random) ${\pm}0.12$ (systematic) (corresponding to a linear distance, $10.19{\pm}0.14{\pm}0.56Mpc$). With this result, we calibrate the standardized candle method of SNe II-P. From the absolute magnitude of SN 2003gd corrected for its expansion velocity and reddening, we derive the value of the Hubble constant, $H0=72{\pm}6{\pm}7km\;s-1\;Mpc-1$. It is in agreement with the uncertainty with the recent estimates based on the luminosity calibration of Type Ia SNe.

• Journal of The Korean Astronomical Society
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• v.47 no.1
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• pp.1-13
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• 2014

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 (${\Sigma}_n$), projected distance ($r_p$), and tidal index (T I) 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 ${\Sigma}_n$, $1/r_p$, and T I, 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 ${\Sigma}_n$, they show a fairly clear dependence on $r_p$ with a high frequency of SB galaxies at small $r_p$. The arm class also exhibits a stronger correlation with $r_p$ than ${\Sigma}_n$ and T I, whereas the Hubble type exhibits similar correlations with ${\Sigma}_n$ and $r_p$. 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.

• Journal of Astronomy and Space Sciences
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• v.2 no.2
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• pp.101-115
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• 1985

Using Brandt model the mess distribution of the late type spiral galaxy NGC 6946 was derived, and the total mass was reestimated to understand the M/L ratio of this galaxy. Two kinds of the rotation curve with shape parameter n=1 and 3.3 were examined. The following are the main results; (1) The total masses of NGC 6946 are $3.1\times$$10^{11}$ M(n=1) AND $2.8\times$$10^{11}$ M(n=3.3) respectively. and the corresponding M/L are about 17 and 16 for both cases. (2) The optical image in the blue light, whose radius is 9.6 kpc, has 8$\times$$10^{10}$ M and 1.4$\times$$10^{11}$ M. These give the value of M/L about 5 and 8 respectively. (3) The masses and M/L of the nuclear region within 1.2 kpc are 4.0$\times$$10^{9}$ M 4.7$\times$$10^9$ M and 3, 4 for both cases. Those of the disk from 1.2 kpc to 9.6 kpc are 7.6$\times$1$10^{10}$M, 1.4$\times$$10^{11}$M, and 5, 8. (4) The masses of the outer halo extended to few hundreds kiloparsecs are 2.3$\times$$10^{11}$ M and 1.4$\times$$10^{11}$M. The corresponding M/L are about 62 and 37.