• 천문학회보
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• 제39권1호
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• pp.38.1-38.1
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• 2014

A non-axisymmetric mass distribution in the galactic bulge (or bar) causes gas flow from the disk to the nuclear region, inducing intense star formation in the nucleus. We investigate the relation between the ellipticity of the bulge and the presence of a nuclear starburst by using a volume-limited sample of galaxies. We use 1,680 spiral galaxies with Mr < -19.5 at 0.02 <= z < 0.05 in the Sloan Digital Sky Survey Data Release 7. We find that the occurrence of nuclear starburst has a moderate correlation with bulge ellipticity in intermediate-type spiral galaxies (morphology classes Sab~Sb) in low galaxy number density environments. In high galaxy number density environments, close encounters and mergers between galaxies can cause gas inflow to the nuclear region even without the presence of non-axisymmetric bulges.

• 천문학회보
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• 제26권2호
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• pp.37-37
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• 2001

• 천문학회지
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• 제38권2호
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• pp.169-172
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• 2005

We present CO(3-2), CO(2-1), and 230 GHz (1.3 mm) continuum images of nearby galaxies taken with the Submillimeter Array (SMA). Our main topic is to study the relation between higher-J molecular gas (e.g., CO J=3-2, 2-1) and nuclear activities (e.g., active galactic nuclei [AGNs] and starbursts). The nearby Seyfert 2 galaxy M51 shows strong CO(3-2) emission from the circumnuclear molecular gas, with an intensity twice as strong as that of the CO(1-0) emission. Strong CO(3-2) emission enhancement suggests that the circum nuclear molecular gas in M51 is warm and dense, which may be related to the AGN activities. Molecular gas in the nearby moderate starburst galaxy NGC 6946 is distributed along the large-scale bar or spiral arms and along the minibar, and the multi-J CO line images show very similar distribution to each other. For this galaxy, there is no clear enhancement in higher-J lines as seen in M51, which may be because NGC 6946 does not have clear AGN activities. Based on the results of these two galaxies, the physical conditions of the circum nuclear molecular gas may be related to the AGN activities. We also observed the nearby edge-on starburst galaxy NGC 3628 and the starburst/Seyfert composite galaxy NGC 4945 with the CO(2-1) line and 230 GHz (1.3 mm) continuum emission. These information will give us some hints for understanding the relation between nuclear activities and circum nuclear molecular gas and dust.

• 천문학논총
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• 제27권4호
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• pp.291-292
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• 2012

We select infrared-luminous galaxies by cross-matching the SDSS spectroscopic sample of galaxies with the WISE all-sky survey catalog. Based on photometric data points covering from SDSS u-band to WISE $22{\mu}m$, their spectral energy distributions (SEDs) are separated into AGN, elliptical, spiral, and irregular galaxy components. The derived luminosities of spiral galaxy and AGN are well correlated with $H{\alpha}$ and [OIII] line luminosities, respectively. Most galaxies are dominated by young stellar populations even for optical AGNs, but at least 10% of optical non-AGNs appear to harbor buried AGNs. The AGN contribution increases dramatically with the total luminosity. These results show that the SED decomposition is successful and is useful to understand the true nature of dusty galaxies.

• 천문학회지
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• 제35권4호
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• pp.175-185
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• 2002

Almost half of primeval galaxies show P-Cygni type profiles in the Ly$\alpha$ emission line. The main underlying mechanism for the profile formation in these systems is thought to be the frequency re-distribution of the line photons in expanding scattering media surrounding the emission source. A Monte Carlo code is developed to investigate the Ly$\alpha$ line transfer in an optically thick and moving medium with a careful consideration of the scattering in the damping wings. Typical column densities and expansion velocities of neutral hydrogen investigated in this study are $N_{H1}{\~}10^{17-20}\;cm^{-2}$ and ${\Delta}V{\~} 100 km\;s^{-1}$. We investigate the dependence of the emergent profiles on the kinematics and on the column density. Our numerical results are applied to show that the damped Ly$\alpha$ absorbers may possess an expanding H I supershell with bulk flow of ${\~}200 km\;s^{-l}$ and H I column density $N_{H1}{\~}10^{19}\;cm^{-2}$. We briefly discuss the observational implications.

• 천문학회지
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• 제34권1호
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• pp.17-24
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• 2001

We have studied the central parts of M82, which is a well-known infrared luminous, starburst galaxy, by analyzing archival data from the Infrared Space Observatory (ISO). M82 was observed at 11 positions covering $\pm$45" from the center along the major axis. We analyzed 4 emission lines, [ArIII] 8.99 ${\mu}m$, $H_2$ 17.034 ${\mu}m$, [FeII] 25,98 ${\mu}m$, and [SiII] 34,815 ${\mu}m$ from $SWSO_2$ data. The integrated flux distributions of these lines are quite different. The $H_2$ line shows symmetric twin peaks at $\~$18" from the center, which is a general characteristic of molecular lines in starburst or barred galaxies. This line appears to be associated with the rotating molecular ring at around $\~$200 pc just outside the inner spiral arm. The relative depletion of the $H_2$ line at the center may be due to the active star formation activity which dissociates the $H_2$ molecules. The other lines have peaks at the center and the distributions are nearly symmetric. The line profiles are deconvolved assuming that both intrinsic and instrumental profiles are Gaussian. The velocity dispersion outside the core is found to be $\~50 km s^{-1}$. The central velocity dispersion is much higher than $50 km s^{-1}$, and different lines give different values. The large central velocity dispersion ($\sigma$) is mostly due to the rotation, but there is also evidence for a high $\sigma$ for [ArIII] line. We also generated position-velocity maps for these four lines. We found very diverse features from these maps.

• 천문학회보
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• 제37권1호
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• pp.37.1-37.1
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• 2012

We present mid-IR (MIR) and near-UV (NUV) properties of red sequence galaxies defined by optical color-magnitude relation. We use the Wide-field Infrared Survey Explorer (WISE) preliminary released data matched with the SDSS DR7/GALEX GR6. The red sequence galaxies with little emission lines show a wide spread of MIR (3.4um-12um) colors, implying a variety of MIR excess emission. We focus on the properties of the red sequence galaxies with MIR excess, comparing the properties of post-starburst galaxies to trace how galaxies migrate to the red sequence.

• 천문학회지
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• 제44권5호
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• pp.151-160
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• 2011

We present a study searching for globular cluster systems (GCSs) of two face-on low surface bright- ness galaxies (LSBGs), UGC 5981 and UGC 6614. Based on HSTWFPC2 images of F555Wand F814W filters, we detect 12 and 18 GC candidates for UGC 5981 and UGC 6614, respectively. Although these two LSBGs have very different bulge properties, they have very similar specific frequencies ($S_N$) of 0.1. However, $S_N$ ~ 0.1 is quite small even for their late morphological types, albeit within errors. This suggests that LSBGs have had star formation histories lacking dominant initial starburst events while accumulating their stellar masses through sporadic star formation activities.

• 천문학논총
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• 제32권1호
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• pp.251-255
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• 2017

Submillimetre and millimetre-wave surveys with Herschel and the South Pole Telescope have revolutionised the discovery of strong gravitational lenses. Their follow-ups have been greatly facilitated by the multi-wavelength supplementary data in the survey fields. The forthcoming Euclid optical/near-infrared space telescope will also detect strong gravitational lenses in large numbers, and orbital constraints are likely to require placing its deep survey at the North Ecliptic Pole (the natural deep field for a wide class of ground-based and space-based observatories including AKARI, JWST and SPICA). In this paper I review the current status of the multi-wavelength survey coverage in the NEP, and discuss the prospects for the detection of strong gravitational lenses in forthcoming or proposed facilities such as Euclid, FIRSPEX and SPICA.

• 천문학회보
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• 제35권2호
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• pp.29.2-29.2
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• 2010

We present elemental abundances of 412 blue compact dwarf galaxies (BCDs) at z=0.2~0.5 using the Sloan Digital Sky Survey (SDSS) DR7. The gas-phase nitrogen to oxygen abundance ratios (N/O) of sample galaxies increase as the oxygen to hydrogen abundance ratios (O/H) decrease. This indicates that the nitrogen is more enriched than the oxygen. We found that there is a noticeable distinction between the merger candidates and the isolated galaxies. Merging candidates show more enrichment of nitrogen abundance compared to isolated galaxies. On the other hand, neon and oxygen abundances for merging candidates are slightly lower than the isolated systems. We discuss the main cause of these trends with internal mixing and mass loss by fast rotation of young massive stars. We also discuss the environmental effect to the relation between specific star formation rate and galaxy mass.