• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.123-144
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• 2003

The 8m class telescopes in the ground-based optical astronomy together with help from the ultra-sharp eye of the Hubble Space Telescope have enabled us to observe forming galaxies beyond red shift z = 5. In particular, more than twenty Ly$\alpha$-emitting galaxies have already been found at z > 5. These findings provide us with useful hints to investigate how galaxies formed and then evolved in the early universe. Further, detailed analysis of Ly$\alpha$ emission line profiles are useful in exploring the nature of the intergalactic medium because the trailing edge of cosmic reionization could be close to z $\~$ 6 -7, at which forming galaxies have been found recently. We also discuss the importance of superwinds from forming galaxies at high redshift, which has an intimate relationship between galaxies and the intergalactic medium. We then give a review of early cosmic star formation history based on recent progress in searching for Ly$\alpha$-emitting young galaxies beyond red shift 5.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.34.4-35
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• 2009

We have studied the radial g-r color gradients of early-type galaxies in the Sloan Digital Sky Survey (SDSS) DR6 in the redshift range 0.00 < z < 0.06. The color profiles of ~30 per cent of the galaxies in this sample show positive color gradients (centers being bluer). These positive gradient galaxies often show strong $H\beta$ absorption line strengths or emission line ratios that are consistent with star-forming populations. Combining the optical data with Galaxy Evolution Explorer (GALEX) UV photometry, we find that all positive gradient galaxies show blue UV-optical colors. They also exhibit a tendency of having a lower stellar velocity dispersion. Positive gradient galaxies tend to live in lower density regions than negative gradient galaxies and are likely to have a late-type companion galaxy. On the other hand, massive early-type galaxies show negative color gradients. A simplistic population analysis shows that these positive color gradients are visible only for half a billion years after a star burst. Although the effective radius decreases and mean surface brightness increases due to this centrally concentrated star formation, the positions of the positive gradient galaxies on the fundamental plane cannot be reproduced by any amount of recent star formation. Instead it required a lower velocity dispersion.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.84.1-84.1
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• 2012

One of the most intriguing questions regarding black hole (BH)-galaxy co-evolution picture is how the BH accretion, or active galactic nucleus (AGN) activity is linked to star formation (SF) activity. While it is suggested that AGN luminosity of quasars correlates with SF luminosity, it is still unclear how AGN activity is connected to SF activity based on host galaxy properties. Utilizing AKARI's unique slit-less spectroscopic capability and wavelength coverage, we probed star formation activity of several types of AGNs by measuring the PAH 3.3 ${\mu}m$ emission. First, we detected the PAH 3.3 ${\mu}m$ emission from seven out of 27 Seyfert type-1 galaxies at z~0.36. While these galaxies deviate significantly from the local Mbh-${\sigma}$ relation meaning their black holes proceed the host galaxies in terms of evolution, they appear to follow the correlation between nuclear SF and AGN activities of local Seyfert type-1 galaxies. This implies that SF and AGN activities are directly connected at the nuclear region for these Seyfert type-1 AGNs. We also obtained 2-5 ${\mu}m$ spectra for subsamples of Quasar Spectroscopic Observation in Near-infrared Grism (QSONG) which consists of reverberation-mapped AGNs and PG-QSOs. We detected the PAH 3.3 ${\mu}m$ emission from 16 out of 31 reverberation-mapped AGNs and 10 out of 49 PG-QSOs and measured their line strengths. We present the correlations between SF and AGN activities and discuss if there is any dependency of the correlations on properties of host galaxies, such as morphology, or the presence of radio jets.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.53.1-53.1
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• 2018

We present the second data release from the SAMI Galaxy Survey. The data release contains reduced spectral cubes for 1559 galaxies, about 50% of the full survey, having a redshift range 0.004 < z < 0.113 and a large stellar mass range 7.5 < log($M_*/M_{\odot}$) < 11.6. This release also includes stellar kinematic and stellar population value-added products derived from absorption line measurements, and all emission line value-added products from Data Release One. The data are provided online through Australian Astronomical Optics' Data Central. Our poster presents stellar/gas kinematics on the metallicity-mass plane and highlight several galaxies from the SAMI Galaxy Survey that have interesting stellar and gas kinematics. For more information about data release 2, please see: https://sami-survey.org/abdr.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.48.2-48.2
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• 2012

We present preliminary results of a statistical study on the nuclear activity of compact group galaxies. What triggers Active Galactic Nuclei (AGN) is still a puzzling problem. One of the suggested AGN triggering mechanisms is galaxy-galaxy interaction. Many simulations have shown that gas can be supplied to the center of galaxies during galaxy encounters. In this regard, compact groups of galaxies are an ideal laboratory for studying the connection between galaxy interaction and nuclear activity because of their high densities and low velocity dispersions. We study the environmental dependence of the activity in galactic nuclei using 59 compact groups in the SDSS DR6. Using the emission line data, we classify galaxies in the compact groups. We find that 19% of the compact group galaxies are pure star-forming nuclei, 10% as transition objects, and only 7% of the galaxies in compact groups show the nuclear activity. The AGN fraction of compact group is higher than galaxy clusters, but lower than field environment. Implications of this result will be discussed.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.157-161
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• 2017

The dusty torus of Active Galactic Nuclei (AGNs) is one of the important components for the unification theory of AGNs. The geometry and properties of the dusty torus are key factors in understanding the nature of AGNs as well as the formation and evolution of AGNs. However, they are still under discussion. Infrared observation is useful for understanding the dusty torus as thermal emission from hot dust with the dust sublimation temperature (~ 1500 K) has been observed in the infrared. We have analyzed infrared spectroscopic data of low-redshift and high-redshift quasars, which are luminous AGNs. For the low-redshift quasars, we constructed the spectral energy distributions (SEDs) with AKARI near-infrared and Spitzer mid-infrared spectra and decomposed the SEDs into a power-law component from the nuclei, silicate features, and blackbody components with different temperatures from the dusty torus. From the decomposition, the temperature of the innermost dusty torus shows the range between 900-2000 K. For the high-redshift quasars, AKARI traced rest-frame optical and near-infrared spectra of AGNs. Combining with WISE data, we have found that the temperature of the innermost dusty torus in high redshift quasars is lower than that in typical quasars. The hydrogen $H{\alpha}$ emission line from the braod emission line region in the quasars also shows narrow full width at half maximum of $3000-4000km\;s^{-1}$. These results indicate that the dusty torus and the broad emission line region are more extended than those of typical quasars.

• Journal of Astronomy and Space Sciences
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• v.30 no.1
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• pp.59-67
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• 2013

We present a spectroscopic study of 343 blue compact galaxies (BCGs) at 0.20 < z < 0.35 from the Sloan Digital Sky Survey (SDSS) DR7 data. We derive gas phase oxygen abundance using the empirical and direct method. Stellar masses of galaxies are derived from the STARLIGHT code. We also derive star formation rates of galaxies based on $H{\alpha}$ emission line from the SDSS as well as far-ultraviolet (FUV) flux from the Galaxy Evolution Explorer GR6 data. Evolution of the luminosity-metallicity and mass-metallicity (M-Z) relations with redshift is observed. At a given luminosity and mass, galaxies at higher redshifts appear to be biased to low metallicities relative to the lower redshift counterparts. Furthermore, low mass galaxies show higher specific star formation rates (SSFRs) than more massive ones and galaxies at higher redshifts are biased to higher SSFRs compared to the lower redshift sample. By visual inspection of the SDSS images, we classify galaxy morphology into disturbed or undisturbed. In the M-Z relation, we find a hint that morphologically disturbed BCGs appear to exhibit low metallicities and high SSFRs compared to undisturbed counterparts. We suggest that our results support downsizing galaxy formation scenario and star formation histories of BCGs are closely related with their morphologies.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.71.1-71.1
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• 2012

We have identified local analogs of strong $H{\alpha}$ Emitters (HAEs) that dominate the z~4 Lyman-break galaxy population using the Sloan Digital Sky Survey (SDSS). At z<0.4, only 0.04% of galaxies are classified as HAEs with $H{\alpha}$ equivalent width larger than $500{\AA}$, comparable to that of z~4 HAEs. The $H{\alpha}$-to-UV luminosity ratio of local HAEs is consistent with that of z~4 HAEs, indicating relatively large specific star formation rate in these galaxies compared to traditionally studied UV-selected Lyman break analogs. Local HAEs are young, less evolved galaxies with low metallicity. It is still difficult to constrain whether the star formation in local HAEs is powered by minor mergers or by cosmological cold gas accretion. However, the stacked optical spectrum of local HAEs shows several strong ionization lines, for example HeII 4686 emission line, which are shown in Wolf-Rayet galaxies. Thus it is highly likely that local HAEs are galaxies with an elevated ionization parameter, either due to a high electron density or large escape fraction of hydrogen ionizing photons.

• Journal of The Korean Astronomical Society
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• v.33 no.1
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• pp.1-17
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• 2000

We have performed extensive simulations of response of gaseous disk in barred galaxies using SPH method. The gravitational potential is assumed to be generated by disk, bulge, halo, and bar. The mass of gaseous disk in SPH simulation is assumed to be negligible compared to the stellar and dark mass component, and the gravitational potential generated by other components is fixed in time. The self-gravity of the gas is not considered in most simulations, but we have made a small set of simulations including the self-gravity of the gas. Non-circular component of velocity generated by the rotating, non-axisymmetric potential causes many interesting features. In most cases, there is a strong tendency of concentration of gas toward the central parts of the galaxy. The morphology of the gas becomes quite complex, but the general behavior can be understood in terms of simple linear approximations: the locations and number of Lindblad resonances play critical role in determining the general distribution of the gas. We present our results in the form of 'atlas' of artificial galaxies. We also make a brief comment on the observational implications of our calculations. Since the gaseous component show interesting features while the stellar component behaves more smoothly, high resolution mapping using molecular emission line for barred galaxies would be desirable.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.281-285
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• 2017

We present a summary of our spectroscopic redshift catalogue of 404 sources in the AKARI Deep Field South (ADF-S). We have used the AAOmega spectrograph to target mid-infrared and far-infrared sources selected primarily from AKARI observations in this field for which we were able to obtain optical counterparts. Our sources with identified redshifts include 316 with $H{\alpha}$ detections at $z{\leq}0.345$ and 15 sources at z > 1 with MgII or $Ly{\alpha}$ emission lines. About 13% of our $z{\leq}0.345$ sources are dominated by active galactic nuclei (AGN) emission, although many show emission from both star formation and AGNs. The median Balmer decrement is 5.9. Ultra-luminous infrared galaxies (ULIRGs) were found only in the higher-redshift sources. Optical and near infrared data will be available shortly, enabling calibration of the line luminosities and spectral energy distribution (SED) fitting for these sources.